designing a rifle and would like some input


April 13, 2014, 11:05 PM
hey everyone, i am working on designing a rifle right now and i was looking to get some community input on it.. when i have finished designing it i will give the blueprints/plans to everyone here.. but the main purpose of it is this.. whether you love AR-15s, AKs, FALs, HK-91s or whatever it is you like, all of these rifles are designed for military, with the manufacturing support of entire countries.. im designing something that has more of the consumer in mind.. something for the people

so, with the people in mind im looking to design something that isnt going to have to rely on major factory equipment like huges presses and large injection moulding or anything like that..

the trigger housing will be folded and welded sheet metal not too dissimilar from the FAL lower.. but this trigger housing will contain an AR-15 trigger group and a trunnion designed to attach an AR-15 buffer tube and any AR style stock

the upper will hopefully be a square or rectangular piece of tube steel, but if for some reason this isnt going to work out then will shoot for a very simple folded shape.. either way itll have rails spot or plug welded inside and a front trunnion that will be TIG welded or riveted in

i will probably drill and tap a couple spots on the under-side of the front trunnion, and add a threaded screw-plate behind the magwell to allow different magwells to be used, they would screw in under torque in four locations and can be removed and replaced or changed.. first i will be working on FAL and AR-15 magwells for this

for the barrel i havent decided for 100% what i will do.. i thought about using a barrel extension that contains the locking lugs and using a SCAR kind of system for attaching the barrel which uses screws through the sides of the receiver, and ive also thought about just using savage 10 series barrels which thread into the trunnion by hand over top of a headspacing gauge and is then fixed to the receiver via a barrel nut

i was also thinking about extending the top half of the receiver out to the gas block for a single top rail that stretched from the gas block to the rear of the upper receiver.. and have a handguard attach to this

also, im trying to determine what i will do for the bolt.. just messing around ive designed a 5-lug bolt, a 3-lugged triangular bolt, and one that utilizes two locking lugs similar to a mauser bolt.. but then later changed this idea to using the interchangeable bolt heads available for savage 10 bolts.. but i wanted to go with a simpler, possibly SCAR kind of carrier but this isnt possible with a 2 lug bolt as it requires roughly 80 degrees of rotation which cannot be machined into the carrier without removing a large portion of the carrier.. like the AK bolt

so right now im trying to decide if i should go with a 5 or 6 lug design, or still use the savage two-lug bolt and instead of machining the cam groove into the bolt carrier, instead i machine it into the bolt body.. place the cam bolt in the bolt carrier instead


so, id like to get some opinions on some of these ideas. get some feedback, hear some new ideas.. bottom line is that this isnt just going to be my rifle, but anyone who wants it since im focusing on simple to make parts, off-the-shelf parts (such as the AR trigger group and possibly savage barrels), and im going to give out the plans/blueprints freely so if anyone wants to make their own they will be free to do so...

so.. what do you think?

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April 14, 2014, 07:19 AM
In simple terms, a people's rifle should be able to be assembled by nearly anyone. The AK sure can't, and basing the design on the AR features would be a major improvement. That is because it's modular and meant to be assembled without any presses or special tooling.

I would certainly use the AR barrel extension and bolt, precisely because it doesn't require pressing it into a receiver and simultaneously setting headspace. The barrel extension on the AR screws on, and with a micrometer like adjustment, the headspace is set and then the extension friction pinned in place. It's NOT gunsmith level work and that is the beauty of it on the assembly line.

On the other hand, when Armalite designed the AR10 and M16, it was meant to showcase some advanced methods, and the forged aluminum receiver was the result. It's appropriate for mass production in an advanced technology environment, and does reduce weight and cost in high volumes, but the upfront costs are also high. In extremely low production or low cost manufacture, a folded sheet metal lower and even upper would be much more appropriate. The 1" ID upper could definitely be fabricated from tubing. The makers of monolithic uppers are even using extrusions, not forging, to reduce the costs even more.

I speculate that someone could go into business successfully selling an upper and lower that aren't forged but do take all the AR parts. And a simplified version build to look like a traditional manual action with wood stock wouldn't be out of place. A left side straight pull "bolt action" would be the result.

The M16 has influence a lot of battle rifle designs in the last 50 years, mostly because of the controls and barrel extension concept that are widely copied. They work, in the SCAR or BLR. Sounds like a good project to adopt them, because the extremely simple construction and lack of involved assembly are the key points to a people's rifle. With the combined cartridges available in barrel and bolts for the AR10 and AR15, there's over one hundred to fit nearly any taste. That alone should make it the preferred choice for parts.

April 14, 2014, 05:31 PM
well problem with the AR-15 bolt is it wont work with a SCAR/ACR/AR18 style receiver.. and id like to use a bolt thats a bit stronger too, as well as something larger since im designing this to be a .308 rifle with the capability of swapping out a barrel, bolt head (not necessarily the entire bolt) and the magwell to fire 5.56mm or other calibers in between

so im looking at savage 10 bolt heads but also have drawn up a design for a 3-lug, and a 5-lug bolt.. the two-lug savage bolt due to needing 80 degrees of rotation to lock would need to have the cam groove on the bolt body itself and not the carrier

interchangeable magwells will be bolted or screwed on so they are easily removed.. or riveted if you have no interest in changing the magwell,

i have yet to decide a few things.. do i use the SCAR type of barrel which has the locking lug surfaces in the barrel, and the barrel is basically slid into the receiver and held with four T-25 screws?.. or do i use the savage 10 barrels which thread on by hand over a headspacing gauge and is then locked in place with a barrel nut?... do i go with the two, three, or five lug bolt?.. there are pro's and conts to each

and lastly, since the upper half of the receiver will be extended out to the gas block (for a full length top rail), should the charging handle be on the fore-end, on the side of the receiver, left or right side, reciprocating or non reciprocating?

so still many things left undecided at this point

bottom line though.. AR-15s are easy to assemble, but costly and difficult to make from scratch, even machining out an 80% receiver is quite difficult.. my rifle will use a sheet metal or tube steel upper requiring only rails to be spot or plug welded in.. even the bolt will be significantly easier to fabricate than the AR bolt.. so not only will mine be easier to fabricate, but with only two.. MAYBE 3 springs in the entire upper receiver and fewer small parts itll be a lot easier to assemble than an AR too, if you could get the parts made by someone else

April 14, 2014, 09:26 PM
a trunnion designed to attach an AR-15 buffer tube and any AR style stock

Not sure if you are intending to use the buffer tube as a receiver extension like in an AR or not, but my vote is not. Keep the bolt out of the stock so the gun can be fired with the stock folded.

As far as the lockup system, something like the AR or AK has a big advantage over a traditional bolt gun that locks the bolt to the receiver. The AR's barrel extension and the AK's front trunnion both keep the forces and complex machining to a small part that can then be attached to a more easily made and less strong receiver. The advantage is in making sure the serialized part has as few difficult machining operations as possible. I've honestly wondered how long before we see a bolt action with a barrel extension design...

Have you looked at the AR-180?

April 14, 2014, 09:50 PM
i intend on using some form of a front trunnion, have to for a sheet metal or tube steel upper.. whether the surfaces the lugs lock against will be in the trunnion itself or in a barrel extension held by the trunnion remains to be decided

and the buffer tube attachment is purely for the installation of AR-15 stocks, nothing more, its going to use likely a two-spring recoil system that will be captive, so it wont just fly out when the receiver is taken apart.. i may design it to have a hinged side folding mechanism with a buffer tube adapter though so you can take off the shelf AR-15 stocks and use them as a side folding stock

what im focusing on is whats the cheapest and easiest to machine, i want to rely on the fewest number of maintenance parts as possible.. so the least amount of springs and small parts as i can.. what will be important is that the end user can easily assemble it, and someone with a small machine shop can easily machine the parts

also, i think it is important to have the entire travel of the bolt carrier in the upper.. buffer tube will only be for holding a stock and will have no springs.. i think its also important to have the magazine whether interchangeable or not, securely fixed to the upper.. it shouldnt have to rely on hinges, pins, or anything that can provide wiggle room, this should be a very firm connection.. the carrier needs to ride on rails.. lesser steel on steel contact surfaces will operate more smoothly.. and lastly, there needs to be some amount of mass to the carrier.. carrier-mass contributes more to an AKs reliability than any other feature


so yeah.. if anyone has any ideas or would like to discuss this further we should pick individual features to discuss at a time to keep things organized

April 15, 2014, 10:03 AM
Just make sure you don't accidentally recreate an ar-180. I think their lower was all stamped.

April 15, 2014, 10:14 AM
Sounds fairly similar to the Leader T2; which is basically a simplified AR18.

If you want it to be produced in a small machine shop, you definitely do not want to the an AR-type many-lug bolt. That is not a simple thing to fabricate.

April 15, 2014, 05:09 PM
well as of now nothings concrete.. still in its earliest stages.. havent even decides yet if i wanted a rotating bolt or a forward locking tilting block likely based off a CZ-58.. but im leaning towards rotating for a few reasons though tilting would likely be much simpler and easier to machine.. kind of 50/50

actually, im not even sure just how important interchangeable calibers are.. AK doesnt have them, FAL doesnt, M14 doesnt.. but then again this is a rifle designed for the gun owner and not a military and the consensus seems to be that people love being able to buy one gun and do everything with it.. so thats why im focusing on making it a .308 caliber rifle, but with the change of a bolt head, barrel, and magwell it could just as easily be a 5.56mm rifle

heres the three lug design im working on.. ive also been working on a couple different ideas for extractors.. since id like to have bolt heads that are interchangeable for inexpensive caliber changes, i thought it would be important to focus on an extractor contained within the bolt so each bolt head would have its own extractor specifically for that cartridge.. and i cut a slut for a frame-mounted ejector to aid in reliability by reducing the moving parts and springs needed for a bolt mounted ejector.. but im flexible with that decision

April 15, 2014, 05:16 PM
You should make it so +80% of the weapon can be printed on a home model 3D printer, and all you would need to do is buy a factory barrel, magazine, and get something at the hardware store for a bolt and mainspring.

The reciever, trigger group parts, and furniture could be plastic.

Heck, if the LuLz Liberator can fire a 380 with plastic barrel, then any rimfire or shot shell cartridge would be an option.

April 15, 2014, 05:52 PM
I assume this is designed to be open source so anybody who wants to can pay a few bucks for plans and build away? If so I may play along.

April 15, 2014, 06:18 PM
well im just going to release the plans for free when its done.. probably via maybe register it under a license where i get a small royalty if someone wants to manufacture parts or rifles for other people.. or maybe just go on donations

also, im avoiding the use of 3D printing any parts right now.. 3D printing is not a very strong and reliable means to make something thats going to take some abuse.. its literally melting one layer of plastic on top of another.. and anyone who knows anything about welding can tell you that melting one piece of material on top another will not hold much of a bond at all..

however, certain parts could be injection-molded such as the trigger frame or the magwell.. since the magwell is separate it can be folded sheet metal, machined aluminum, or injection molded polymer.. it all gets attached to the rifle in the same way

heres the bolt as i have it now.. ive simplified the extractor using the AK style extractor.. this only requires drilling a hole into the front of the bolt and the extractor is made from a a solid metal cylinder.. you can see where the spring goes, and where the pin is used to hold it in and give it something to pivot on.. benefit of this extractor is it can be part of the bolt head, allowing bolt heads to be interchangeable

April 15, 2014, 08:28 PM
well ian.. i just watched your video of the leader T2.. and yeah.. thats almost exactly the same bolt.. i had the idea of using a polygonal shaped bolt for ease of manufacturing and thought two wouldnt be neough, 5 lugs would be too much and settled on the triangle.. im actually glad to see this because it validates the design of the bolt

ive also been thinking about going with two recoil springs and guide rods.. but ive been asking myself if these guide rods should lock into the rear of the trunnion and act as rails too or if im better of spot/plug welding rails into the upper.. if i do use the guide rods as the rails then there actually wouldnt need to be any welding done to the receiver.. the front trunnion could just be installed via rivets like an AK trunnion.. and if the lugs lock into recesses in a pre-headspaced barrel such as they do on the AR-15, containing all the pressure of the cartridge inside the barrel then the trunnion could possibly even be made of aluminum and save a lot of weight.. use a steel bushing where the gas piston rod contacts the trunnion so theres no aluminum on steel friction

this has also got me thinking of the steyr AUG which uses two guide rods which i believe also act as rails.. but instead one of these guide rods also acts as the piston.. a non-reciprocating charging handle could act upon the other guide rod which in this case could be fixed to the carrier.. and if the springs were inside those guide rods.. all youd need is a couple rods to go inside of those to push against the spring.. then with absolutely no springs behind the carrier the upper receiver could be significantly shortened, saving weight and making a much more compact rifle

now i can do all of this whether i use the triangle bolt or if i adopt and modify the CZ-58 tilting block system.. where the block doesnt tilt, but has sort of retractable locking lugs that are forced into the recesses when the carrier is forward.. i could maybe make this type of system compact enough to fix into the recesses of a barrel.. like how a remington 870 bolt works.. the gas system, recoil system, and interchangeable bolt faces would be present in either design

so my question to you guys is this.. front locking tilting bolt design that uses retractable locking lugs like that of the remington 870 and CZ-58.. or the triangle rotating bolt similar to that of the leader T2?... or does anyone have any other ideas they may find worth consideration?

April 15, 2014, 11:27 PM
As I'm sure you know by now, there's advantages and disadvantages to the different bolt types. The bolt concept you showed, while simple to produce, has tapered lugs that have less surface area for a given diameter than a square of the same profile (like the Stoner bolt), so while probably simpler for a guy with a mill to carve up, it will need to be bigger/heavier than absolutely needed.

The advantage of a rotating bolt over a tilting bolt (or locking piece) is twofold; first, the bolt can be incredibly short --theoretically the length of the lugs-- and second, the bolt face does not move relative to the cartridge, since both are co-axial. The obvious disadvantage of a rotating bolt is that the trunnions/extensions and bolt heads are very difficult to machine. Yes, you can use off the shelf AR parts for the hard stuff, but by that logic you will invariably end up building an AR clone; parts commonality for the sake of parts commonality leads to you designing new platform for the sake of a new platform. A truly better/different design will be fairly incompatible, and that is unavoidable.

The advantage of a tilting locking piece, and more so, a tilting bolt, is that the bolt is extremely easy to machine, as is the receiver. However, unless you are attempting a tilting-bolt design that tilts at the front, its locking lugs will be further back, requiring more of the receiver to be built to carry immense bolt thrust. And if you tilt the front of the bolt, you will find it extremely difficult to design get enough lug engagement without a ton of bolt motion relative to the case head, which makes extraction and feeding much more complicated. One benefit to the tilt bolt that the rotating will never achieve, is the ability for an open breach; the VZ58 exposes nearly half the action (and the magwell nearly the entire other half) when the bolt carrier is retracted; something an AR can only dream of --just try fishing a jammed primer or other debris that makes its way into the barrel extension out by hand, but on the VZ an index finger can quickly and easily brush out the locking rails and you can visually glimpse right into the chamber. Tilt bolt actions with exposed bolt carriers like the VZ/SKS are also much more easily convertible to belt-feed (UK59 is a belt fed VZ58). The benefit of separate locking piece designs is they move the lugs forward, allowing more of the gun to be flimsy and lightweight, but at the cost of added complication and expense.
(staring straight down through the VZ58 locking lugs, magwell, and breach)

Another action variety you may not have thought about is the Degtyarov, or locking flap. You have a central bolt body that is simply reciprocating into the chamber to feed rounds, with two locking flaps on either side that are pushed outward into recesses by the bolt carrier. The open-bolt designs (not legal in the US) are stupid-simple, but even a striker/hammer fired closed bolt is very simple to visualize, and there is no easier receiver to make by hand; it's basically a tube with two notches cut in the sides. These are also by far the easiest to convert to belt feed (hence why the DP28/DPM had a belt conversion, and all subsequent variants like the RPD and DShK were belt fed). The "Skorparev" compact carbine design I am working on is a miniature DP28 in 7.62x25, and has a receiver built from telescoped steel tubes brazed together and extremely simple bolt pieces (nearly two-dimensional machine parts). I differed from the true rear-locking Degtyarov designs by putting the locking lugs up front (first attachment), which makes the beefy part of the receiver shorter, but also makes the flaps more complex; the DP28 flaps are 1/8" thick rectangular plates with a rounded end --hard to get simpler than that.
RPD, DP28, and DShK bolts, all in a row (the Degtyarov Trifecta :cool:)
And, my Skorparev concept. The idea here was as small/light a legal-length straight stock rifle as possible, cheap and easy to make, that is gas operated, uses PPSH drums/mags, and is automatically ambidextrous (has auto-switching ejection based on user hand position)

Another design I am almost positive you have not considered, is the falling block. If you think about it, a falling block is basically a front-tilting bolt with a really long swing radius. Not very many semi-autos have exploited this concept, but the Madsen LMG was/is a very dependable if awkward looking design. I am pursuing this design for my MP57 project in 5.7x28, since the tilting bolt requires very little momentum to operate, making it in my mind perfect for super small magnum cartridges. Falling blocks are the linear analogue to the rotating bolt, and they posses all the same benefits such as extremely efficient load transfer and extremely compact size. One huge benefit over all reciprocating bolt designs is there is no reciprocation along the barrel axis, so the overall length of the action is equal to the cartridge. The lone detraction is a big one; they require the entire bolt face to scrape over the chambered case head, and a separate mechanism to extract/feed the new round. This is very foreign to folks who are all used to reciprocating bolts doing this work, but the job of feeding/extracting falls to the bolt carrier in the case of a repeating falling block. But check out the second attachment to see just how easy the 'barrel extension' is to make. For my rifle, the extension is milled into the barrel blank itself before chambering, and is the only structural part in the whole gun --the rest is low stress stuff, just like in an AR. But see how much more compact it is (the dark grey square on the end of the 16" barrel is the entire receiver, and contains everything; a small tappet piston out front of the chamber powers everything)
And here's the Madsen LMG. You think a Broomhandle Mauser has weird internals, this thing is like nothing ever seen before or after, and ran like a top up against contemporaries like the Browning BAR :what:. Still in use in Rio, I hear. Ian ( has an excellent video and discussion of the operation and internals, as well as a comically-badass run and gun session (
Incomprehensible operation and machine work, brilliantly simple magazines --too bad they are in a terrible place, which is why I opted to figure out a why to use PS90 mags for the MP57 design.


April 15, 2014, 11:32 PM
Sorry for the humungulungus post replete with mesmerizing animations. Gun design is just one of those things I get really excited about when I see people with know-how getting involved. Disclaimer: If you don't have a real good understanding already, be sure to bone up on the assorted NFA/GCA/local gun building laws, as well as an understanding of ATF regulations/recommendations regarding your particular design. Seek out the info before building it and posting the proof on Youtube :D (Disclaimer over)


April 16, 2014, 12:18 AM
It's totally backwards thinking to the rest of this thread but I would love to see another browning recoiling barrel. Make that happen in a pistol cal carbine and it would be an old school new school combo that would be neat. With modern steel it should be able to be downsized to take the smaller rounds easily. The length of travel would be dependent upon springs and recoil so it should be easy to build long to take everything from .380 to 10mm build it longer and heavier and you have rifle caliber capability. Make your reciever 4 ft long and you can handle 338 lapua and 50bmg...maybe

April 16, 2014, 12:40 AM
i really like the locking flap idea.. seems very similar to another idea i was working on.. it seems very similar to a tilting bolt, but improved

as to the falling block.. no, i didnt even consider that.. its a very interesting LMG.. unfortunately the footprint on it is huge but its nice to see interesting and different designs like that.. todays guns all look and function alike and i honestly find it to be quit boring so im always attracted to the more exotic

as for tilting block, the idea i had in mind was more along the lines of the CZ-58 but front locking.. but im going to look more into the DP-28 mechanism as its so close to something else i thought of that i think it warrants a bit more investigation

April 16, 2014, 12:45 AM
Out of curiosity, are you looking long term at bull pup or standard configuration?

April 16, 2014, 12:47 AM
And are you side, top, bottom, forward ejecting?

April 16, 2014, 12:48 AM
That Madsen is recoil operated, and shot 8mm, so the concept of a recoil-op rifle is very sound (the MG42 was, too). The problem with pistol cal rifles is the barrel is so heavy that the recoil won't budge it. Not to mention a tilt-barrel like you almost always see is a total no go. So, you're stuck with straight-recoiling designs which require the receiver to ride the whole length of the barrel (heavy, $$$). One possible option is the Pedersen hesitation lock, which manages an essentially recoil-operated action along with a fixed barrel (it's a hybrid of blowback and recoil-op) but I wouldn't want to be the small businessman trying to market this following Remington's act on the R51 (or the Model 51, either, since that was a tough act to follow :) )


April 16, 2014, 12:54 AM
Do you have any knowledge or schooling in firearms grade steel selection and heat treatment?

That's going to be a dangerous hurdle for you to jump if you don't!


April 16, 2014, 12:55 AM
"as to the falling block.. no, i didnt even consider that.. its a very interesting LMG.. unfortunately the footprint on it is huge"

You may want to take a closer look. The Madsen is huge because it's recoil operated, and the barrel/breechlock have to slide around inside a sturdy housing. Compared to a BREN (a comparable LMG with similar mag placement) the action is very stubby. The actual breechlock is no longer than an 8mm cartridge, and you would be operating it via piston or gas pressure that adds no additional length as opposed to letting it slide around. It is actually the shortest you can make a firearm action without a moving barrel (blow forward is shortest).

Here's a snubbie in use by Rio police:

"Do you have any knowledge or schooling in firearms grade steel selection and heat treatment?"
Use 4130-type carbon steels and you can hardly go wrong. Just design with a healthy safety factor, avoid super-hardened steels, and test carefully and incrementally, and it's pretty much impossible to blow yourself up. As I recall, the BREN receiver was straight mild steel, and it was a rear-locking arrangement, too :eek:. Just add enough metal and you're covered. The Skorparev is designed to withstand 90,000psi ultimate loads, 60,000psi proof loads, and 40,000psi operating loads, which is more than enough margin to cover my butt :D


April 16, 2014, 01:02 AM
Out of curiosity, are you looking long term at bull pup or standard configuration?
i wouldnt mind the ability to make the rifle adaptable in terms of its configuration.. i mean, with interchangeable bolt heads, a left ejecting bolt can be installed.. with some ambidextrous mechanism for the charging handle you could easily convert it to a left handed rifle.. so why not allow it to be easily expandable for a bullpup, or even a full-stock rifle (like the SKS).. and ejection will be either side.. itll be switchable

so the way i had it envisioned now is i was planning to extend the top half of the upper receiver out to the gas block.. the lower handguard would contain the bottom and side rails and would just hook onto the gas block, then somehow lock to the receiver in the rear.. to take down the rifle i wanted to re-use the mainspring to add tension to the latching mechanism.. like on an AK.. so if someone made a bullpup stock you could remove the lower receiver and the lower handguard, hook a one piece stock in the front on the gas block and latch it in the rear just like the original lower receiver.. maybe make trigger packs that can easily be installed

ive also been thinking of using a striker fired trigger group so that the striker itself could have an extension on it brought to the front of the action so the trigger, disconnector can both be moved forward and the linkage that would normally be between a front trigger and a rear trigger will instead be on the striker itself with no need for a rear trigger or disconnector.. and there should be plenty of clearance near the bottom of the upper receiver for that linkage


im going to look more into the DP28 and similar mechanisms.. that idea is really starting to grow on me as a very compact, very strong, simple to machine system but since i want the ability to change calibers which likely means having whichever bolt.. any bolt lock to the barrel so i will have to make the DP-28 setup front-locking

April 16, 2014, 01:07 AM
"as to the falling block.. no, i didnt even consider that.. its a very interesting LMG.. unfortunately the footprint on it is huge"

You may want to take a closer look. The Madsen is huge because it's recoil operated, and the barrel/breechlock have to slide around inside a sturdy housing. Compared to a BREN (a comparable LMG with similar mag placement) the action is very stubby. The actual breechlock is no longer than an 8mm cartridge, and you would be operating it via piston or gas pressure that adds no additional length as opposed to letting it slide around. It is actually the shortest you can make a firearm action without a moving barrel (blow forward is shortest).

Here's a snubbie in use by Rio police:

"Do you have any knowledge or schooling in firearms grade steel selection and heat treatment?"
Use 4130-type carbon steels and you can hardly go wrong. Just design with a healthy safety factor, avoid super-hardened steels, and test carefully and incrementally, and it's pretty much impossible to blow yourself up. As I recall, the BREN receiver was straight mild steel, and it was a rear-locking arrangement, too :eek:. Just add enough metal and you're covered. The Skorparev is designed to withstand 90,000psi ultimate loads, 60,000psi proof loads, and 40,000psi operating loads, which is more than enough margin to cover my butt :D

also, you can actually select the alloys and hardness of your metals and run a stress simulation at various amounts of pressure and see the results it has on the parts.. face it.. we have it easy.. the gun designers that started these ideas deserve tons of respect for having to do it without modern luxuries of 3D CAD, simulation software, and CNC machining

April 16, 2014, 01:18 AM
I wouldn't put too much faith in FEM, even if it does generate pretty pictures; at the end of the day, the model is still based upon your assumptions so you must remain skeptical (it is pretty cool, though :D)

"wouldnt mind the ability to make the rifle adaptable in terms of its configuration"

One modularity idea I had that seemed worth someone else's time was to split the mag well; think of an AR upper/lower, only the front half of the magwell is integral to the upper. This would allow an upper change to alter the length of the magwell, resulting in a far greater variety of cartridges that could be quickly swapped in. Taken further, the Degtyarov bolts are obviously very scalable, so quickly designing them for a multitude of cartridge lengths and case heads would be a snap. You'd be limited only by how fat a single-stack magazine you could fit in the magwell (or you could use the magwell itself as an internal magazine for the biggest stuff, with feed rails integral to the upper)


April 16, 2014, 02:22 AM
go to the future weapons website or look them up on youtube.. look for the G41 rifle.. that is EXACTLY the mechanism i had envisioned, started drawing up this idea only to find out the germans beat me to it by about 70 years... the idea i had envisioned for a front locking system with retractable lugs was to put the lugs on the inside like that and use the firing pin to push them apart.. i had no idea how id get the carrier to pull the firing pin back.. was thinking of having a knob on the rear section of the firing pin or striker that the carrier would push against to unlock the bolt but this system works too

also, looking at the G41 bolt ive also been thinking you could make the body of the bolt out of a steel pipe, or thick walled steel tubing.. maybe even thread the front of the bolt body and have interchangeable bolt heads that just thread into the front of the bolt body.. or just push one into the front and drive a pin through to pin the bolt head into the tubular body

its very similar to the DP-28 and RPD but is front locking and the entire system is narrow enough that this could easily be designed to lock into a barrel extension

downside of this system as he points out in the video is that if the two lugs arent perfectly matched.. then all the force would be on one lug which would easily break and cause a major failure so you have to ensure both lugs are precise.. but it seems the DP28/RPD locking system would have those same requirements.. but it doesnt seem like anything that can be solved with some precision CNC machining equipment.. or really careful milling.. what do y'all think?

April 16, 2014, 05:30 PM
ive been looking around at some other ideas and found something that is very simple in function.. strong, reliable, and i believe i can simplify it a great deal and make it work for me.. that is the roller locked system (not roller delayed)

the roller locked system appears to work in the same way as the G41/G43 bolt where the firing pin pushes the rollers out of the recesses in the bolt, locking the bolt into the barrel (as is the case on the MG-42) and with this system you need no cam.. firing pin pushes the rollers out, the fact theyre rollers will push themselves in when the firing pin is pulled a bit and the carrier pulls it back.. very simple and can obviously handle 8mm mauser

April 17, 2014, 01:37 AM
did everyone lose interest?

April 17, 2014, 01:42 AM
I'm still interested... But I have no idea about any of this.

April 17, 2014, 01:54 AM
well what dont you know about?

April 17, 2014, 02:52 AM
At this point I don't even know enough to know what I don't know. This thread has brought out a lot of knowledge and useful information too.

April 17, 2014, 03:48 AM
I'm a bit of a tinkerer, myself. I've not so much designed, but copied the designs of others in some of my home built guns. All I've successfully managed so far area couple shotguns, and the .38 I'm building now looks promising.

I'd be very interested in the design if it can be made at home with the simplest of tools. Most of us don't have lathes and vertical mills, so professional grade machining puts most designs out of reach for the majority.

What can be made with minimal tools usually looks like some 3rd world single shot zip gun cobbled together out of various tubing, hose clamps, rubber bands and duct tape, as dangerous to the shooter as it is to the intended target. Then you have things like the Luty BSP SMG, which will win you a fabulous vacation to club fed.

Ideally, I'd like to see something that can be fabricated at home, similar to the Luty SMG, sans federal prison.

AK receivers can be folded out of a shovel, so I'd start with that level of simplicity, using off the shelf components, but not necessarily gun components. If its going to be semi auto, a magazine and bolt that are compatible, and perhaps a barrel, should be all the components needed, and even the bolt, if simple enough in design, can be manufactured at home. Closed bolt Uzi conversion bolts 'look' simple enough (caveat: never handled one, so they may be more complex than I know). So perhaps keep something like that in mind.

The STEN was successful and it was built out of tubing. Semi auto conversion bolts for those exist, too. Simplicity in design will garner the most successful outcome.

Another appeal has to be price expenditure versus time expenditure. For several hundred dollars, you can build an AR in an afternoon. I'm willing to spend less, work more, and if I can build, successfully, a semi auto rifle for a couple hundred dollars, but spend a week or so, I'm more interested. Partly because I'm broke, and have nothing better to do with my spare time.

April 17, 2014, 04:23 AM
i totally recommend watching some forgotten weapons videos..the videos titled "flapper locking firearms", "g41", "last ditch innovation" highlights the roller locked and roller delayed blowback systems of the gerat 06 and 06H

those videos will provide a ton of information and ill list links before..

April 17, 2014, 04:30 AM
well i actually have two designs im working on.. one is to make a more polished rifle that uses simpler shapes for the receivers.. like tube steel and what not, but be a more polished, more versatile and more adaptable design.. magwells can be removed, calibers can easily be changed, and a full length top rail

the other project im working on which i havent been discussing up till now is i want to make a functioning semi automatic 5.56mm rifle with the least amount of work as possible.. something on the level of simplicity of WWII SMGs like the sten but capable of 5.56mm pressures.. no direct blowback would require an enormous bolt easily jumping the weight up to 15lbs or better.. so i was thinking of utilizing some kind of delayed blowback action or an incredibly simple locking system of some sort


that aside.. i started just rough sketching out a new bolt design.. below i posted a photo of a new bolt i just worked out.. its an early design.. i could make it completely square if i wanted to but this is a basic roller locked system.. imagine there being a carrier for the firing pin thatll spread the rollers apart to lock into the trunnion.. or maybe just a piece that slides over the firing pin that is held in the locked position by the carrier via a slot cut in the top

April 17, 2014, 05:02 AM
I've actually started a design for a roller locking system bolt design myself.

No fancy computer generated images though, just the ones in my head.

April 17, 2014, 05:19 AM
well, you can get a free trial of autodesk inventor.. might be worth a try and its so much easier and better when you can see things physically interact with eachother to determine where weakness or conflicts may be

anyway.. i just sketched up a barrel extension.. but this could be machined into the end of a barrel blank if there enough of it.. this shows how you only need the two ears coming off the barrel for the rollers to lock into... now looking at the photos above.. i had the idea.. the upper receiver is square, the barrel extension is square.. say that barrel extension is 1" x 1".. so say the upper is 1" x 1 1/2".. that would allow the block the barrel mounts into to be screwed into the receiver, closest to the bottom of it and offer plenty of clearance for a gas piston above and the guide rods beside the piston (or go with an AUG like system where one of the two guide rods IS the piston

the other way i see you can go about this is to use that barrel extension piece and rivet it into the trunnion.. then use the savage system of changing barrels where you headspace by hand, then use a barrel nut to tighten down over the top the threads

i was willing to go to 1.5x2" for the receiver dimensions, this would offer plenty of room to simply use what you see below as an extension of the barrel and make a separate trunnion, riveted to the receiver that that extension would fit into.. to make it easier the barrel extension edges can be rounded off, so the internal machining of the trunnion would be rounded off eliminating the need to use anything like a broach for it

lastly.. i just rounded that bolt off to see what it would look like when its smoothed out.. i could just as easily leave it square and cut the entire thing out of a piece of 9/16" square bar, only needing to cut the slots in the bolts for the roller and do some internal boring


just another thought unrelated to the bolt carrier group.. but i was thinking about the gas system.. if the gas system is above the barrel and i extend the top half of the receiver out to the gas block for a full length top rail it would also make it pretty difficult to work on the gas system if it needed to be taken apart or worked on unless the barrel was removed to do so.. do its another reason why ive considered going with a gas system that was under and off to the side of the barrel like on the AUG, because then the gas system and if i place a forward non reciprocating charging handle on the rifle, both things could be accessed simply be removing the lower handguard

April 17, 2014, 08:59 AM
"AK receivers can be folded out of a shovel"
The sheet metal can be, at least. The FCG, trunnions, bolt, carrier, and gas system are all about as complicated as anything else.

The one drawback with roller locks is that you have a line of contact with the bolt and recess, rather than a planar contact, so the interfaces have to be made with very similar radii in order to get a broad effective contact area. Also very hard metal. Otherwise, the rollers will need to be much larger than a comparable planar lug would need to be (also, the Hertzian Contact Stress formula is a bit of a bear to wrangle). The drawback with a milled extension like you have shown is that the rollers will thrust outward nearly as much as they push back, and there is no continuous ring to take the load; this is why MG42 and MP5 trunnions have continuous ring forged trunnions, and why CZ52 roller-locked pistols have a problem with splitting slides due to outward pressure & metal fatigue. Your barrel extension looks essentially like an MG42 barrel's except its locking grooves are cut through windows in the sides (as opposed to completely open sides in the trunnion). If the barrel extension was supported by another ring of material (like if it was pressed/screwed into a strong collar on the receiver tube) this would be a non-issue.

As far as the locking piece, you will definitely want to go with a firing pin sleeve as part of the bolt carrier. If the pin itself does it, the BATFE would probably categorize the device as an open-bolt gun. This would also have the benefit of allowing the bolt/carrier spring to be lighter. Pretty cool ideas so far, though. What magazines do you want to use? This will define a lot of things, and mags are actually one of the more impossible parts to make yourself.


April 17, 2014, 09:09 AM
well those are some interesting points to consider.. i was actually thinking the rollers dont seem to offer too much contact surface between the bolt head and the receiver.. so.. there may be some incentive to lean more towards the G41/G43 system.. but the flapper system isnt ruled out yet though.. i can extend the barrel extension a bit more.. move the hinge for the flapper up behind the bolt head and be able to have simple rear locking flappers lock into the barrel extension of a similar design

so.. if the systems im looking at now theres the roller locked, the flappers, and the G41/G3 front locking retractable locking lugs.. im fairly certain i want to go with one of these systems over a rotating bolt and i do believe it will be a much better design than the tilting bolt

as for the flappers.. just how long do the flappers actually have to be?

as for magazines, im focusing on using two magwells from the start.. magwells will screw to the bottom of the receiver and ill space the four screw holes out enough for .308 length magwells.. for .223 length magwells the front of the magwell will be all the way forward and itll have a tail on the back side to cover the rest of the opening in the receiver and screw into the same screw holes in the back.. im focusing first on the FAL magwell and AR-15 magwell but of course any and all magwells could be made at a later date

i think later on im going to draw up a rough model of what the finished product may look like

Dave Markowitz
April 17, 2014, 09:09 AM
Cool thread.

April 17, 2014, 11:43 AM
for anyone who is interested.. this is a G43 bolt disassembled, you can see the two retractable locking lugs removed and you cans eee how simple the bolt itself is.. barely more than a piece of tube steel with a few slots cut out

this is a flapper style bolt from a DP28 and DPM

and this is the roller locked system (had to go with an MG42 because a smaller, lighter, simpler gerat 06 is hard to find photos for)

April 17, 2014, 09:45 PM
of those three systems above, flapper, the front retractable lugs, and the roller locked systems.. what do you guys like the most?.. what do you think would be the simplest and most reliable system to go with and why?.. im fairly certain id like to go with one of those three over a rotating bolt (which has been done to death, and frankly bores me)

one downside i see to the roller locked system is that realistically you have the entire pressure of the cartridge being places on a relatively small surface area.. look at the grooves the rollers travel in on the bolt.. when you put a round surface against a flat surface theres only so little contact surface between the two

with the flapper locked system, im not sure how accurate this system can be when you have essentially two free-floating plates between the bolt and the receiver to lock it... seems like if there is ANY play at all you could end up with a very sloppy system

and the downside i see to the retracting lugs is its rather difficult to get a large contact surface with the locking lugs because the larger you make them, the further inside the bolt they need to retract and theres only so much space available


the route im taking right now with the roller locked system is to take a lot of inspiration from the G3.. but slim down and simplify the bolt while also changing the cam surfaces so the rollers will lock on a flat surface and not an angled one.. thus making it roller locked... but im going to use essentially the same little roller pack for it and design a new bolt to better suit my needs

April 18, 2014, 06:28 AM
so.. i have kind of a rough grouping of bolt parts that i think could work.. they are two rollers not too dissimilar from the ones in the HK91 rifle and it uses that little clip on top to hold them inside the bolt so they cant fly out.. also, i designed a cam block that will slide inside the bolt and be the surface which pushes the rollers apart

now.. if a roller locked rifle accidently fires when its not in full battery, there will be a major failure.. so im designing this safety feature into it.. the firing pin which protrudes through this cam block will have a section of it that will be a tad larger than the hold in the cam block to stop the firing pin allowing it to only travel a certain distance..

what that means is since the firing pin can only go a certain distance through the cam block, the firing pin simply wont reach the primer of the cartridge until the cam block is fully forward, and that cam piece cannot go fully forward unless the rollers are fully pushed aside and the rifle is fully locked

im thinking about these kind of safety features as i go along.. judging each mechanism to make sure the rifle cannot fire unless its completely safe to do so

this is a rendering of what i have so far.. as you can see its not too dissimilar from an HK91 bolt except ive made the cam block as so that it will be roller locked and not roller delayed.. and i just designed the head of the cam surface for now.. havent decided how this will interract with the bolt carrier but maybe something similar to the G43 bolt carrier

i will admit though that the further i progress with the roller-locked system, the more im realizing that it requires a lot more internal machining that i had hopes as i would have preferred to keep most internal machining like that to just drilling and boring.. hmm, but now that i think about it, all the forces absorbed by the bolt when locked are going to be on the surfaces in front of the rollers, not on the surfaces behind the rollers.. i wonder if i could cut off just behind the opening for the rollers and then use a piece of thick walled steel tubing to make up the back half of a two-part bolt.. that would eliminate all internal machining

April 18, 2014, 11:46 PM
anyway.. put that aside for now..does anyone have any other ideas?.. maybe some other kind of locking mechanism not yet discussed, or any ideas relating to other features?

i was looking through some different rifles.. and i noticed the FG42 and its side magazine which wasnt uncommon for other designs and it got me to thinking... people quickly cast aside the thought of using them.. but i mean there are tradeoffs.. if the magwell is on the side.. then it would be much easier to remove that magwell and design something like the HK21 magwell which would allow feeding from belts.. also when laying prone the size of the magazine wouldnt be an issue

or what if it used a helical magazine (like the calico .22 and the russian PP-19.. but was perhaps top loaded like a P90 to keep the weight and balance rearward?

about the only thing i DONT want to do here is just make some cookie cutter rifle thats just like all the rest that are already out there but instead make one easier to make, as reliable as can be, and still add a bit of something different to it


a question someone may be able to help me with.. its relating to primary extraction.. primary extraction is when the rearward movement of the bolt or the cartridge itself is slowed down to allow a slower pull of the cartridge out of the breach before it gets jerked violently to the rear.. without primary extraction and something that unlocks immediately, this can tear case rims off... now i was thinking about the roller locked system.. it seems like this includes its own primary extraction.. as the rollers begin to move inwards, the amount of contact surface with the locking recesses lessons and the bolt should begin to open slowly as the lugs are being pulled inwards before they are completely unlocked and the rifle completely recoils.. much in the same was a case is partially extracted during firing with a roller-delayed system only this doesnt occur until after the bullet leaves the barrel

so this seems like it would be a good advantage to roller locked... i could be wrong though?

April 19, 2014, 01:21 AM
I would like to share a few pics of my VZ58, which is a tilting bolt design...

Without Magazine...

LOCKED position


April 19, 2014, 01:57 AM
on the CZ-58, the two locking lugs are linked together right?.. and the bolt carrier hits that bridge to push the locking lugs up and pushed the bolt back on that same surface..

you know.. you see so many rifles where you have a giant bolt carrier that does all the work, has the rails, and most the weight that it feels foreign to make the bolt the heavier part, to put the rails on the bolt and use the carrier just to push it


heres an idea that may work well for a bullpup design.. that is, put a catch on the op-rod so the trigger forward of the receiver catches the op-rod before it goes completely forward.. that op rod would be attached to the firing pin and then have an extra inch or so of travel after the bolt locks in which that carrier and oprod can still travel, essentially combining the op-rod into a striker as well.. this is what the FG-42 did, and a company out of texas is making legal semi auto versions.. to use it in a bullpup you could just place the trigger pack and the catch further forward

now to do this in a roller locked or falling breach mechanism is just as easy.. just provide an extra half inch to an inch of travel after the carrier has completely and fully locked the rifle (so it cant be classified as an open bolt mechanism)

one of the reasons i thought about having a side magazine is you can have it eject out the opposite side and be able to reverse it as well so you can switch the magazines and the ejection port.. this would require only two sides of the receiver to be cut for an ambidextrous system as opposed to three and also makes for a fairly straightforward belt-fed option too.. just throwing some more ideas out there to see what people think

April 19, 2014, 02:15 AM
More pics of the bolt. English is not my native language, so I still don't have the full firearms vocabulary implemented, so what do you mean with locking lugs?

April 19, 2014, 02:47 AM
that reminds me of a flapper system... but one that pivots vertically from the rear.. i think its a very good system.. question though.. would it be unsafe to make a similar system that actually pivoted on a large pin?.. then you you could have the blocks lock even with the bolt face and move the system even further forward because its my understanding that block falls between the a ledge on the side of the bolt and into recesses in the receiver to lock.. basically falling between the two.. but would a large pin should it pivot on one instead be able to handle the pressures of a .308?.. benefit is you can then add a tail above the pivot point for the bolt carrier to hit.. makes it a bit simpler.. but then again i could probably simplify what the cz58 does too.. and it looks very simple since it seems to be all external machining

you know, when i really think about it.. the CZ VZ 58 system doesnt seem like its going to work for what i need it for.. no way to access the bridge across the top of the locking pieces and still have the bolt lock in the barrel.. and of the DP-28 style flapper system even if i did make one with really short flappers, they still couldnt lock in a barrel extension without the bolt carrier being able to go over top to actuate them

what i need is a solution that will be front locking.. but actuated or operated from the rear of the bolt so the bolt can be inside the barrel or barrel extension when it locks.. and can be unlocked from the rear.. this leaves me realistically with only three systems.. rotating bolt, roller locked, and the G43 type front locking flappers which are locked and unlocked from the inside of the bolt by a piece that can be set up to be operated from the rear if needed

im going to focus my further efforts from here on on the G43 front locking flapper setup.. its internally locked and unlocked, can be unlocked with the bolt head into a barrel, and itll be easier to machine a locking recess inside the barrel, which means you wouldnt even need a barrel extension... what i will have to do however is add a bigger margin for safety over the G43 system by increasing the contact surface of each lug to a point where the rifle could safely be fired if for some reason it only locked on one of the lugs.. say the other one was worn or broken.. and im going to do the thing i discussed above with the firing pin. put a stop on firing pin so the firing pin cant even contact the primer until that bearing surface is fully forward and the rifle is fully locked


now im getting bored of discussing locking systems.. im looking to discuss other features.. such as magazine placement.. front of the trigger, bullpup, or on the side.. either way its going to be ambidextrous so if its a side magazine the magazine well and ejection port will be made to screw in in place of eachother.. if its a front or rear mag then i will have to make two ejection ports and cover one (like on the FAL)

id also like to discuss gas systems.. i will not go with direct impinged but i can either go with a short stroke or a long stroke.. i thought about copying the AUG a bit with the two guide rods being attached to the carrier.. which also allows them to be used as rails so welding rails in the receiver wouldnt be necessary, and with springs inside them the action can be shortened considerably and the function of one of these rods can be a gas piston, the other used for a non reciprocating charging handle.. even make the functions swappable for ambidexterity.. but im not opposed to welding rails into the upper prior to heat treating it and just going with a single piston system

so lets discuss something besides locking systems for a while.. anyone have anything else theyd like to discuss or ideas theyd like to share?

April 19, 2014, 07:12 PM
About the gas systems, well, the obvious disadvantage of the Direct Impingement is that you have hot gas and carbon fouling blowing into the action... but you said you will not go with DI so let's discuss long stroke and short stroke. Let's start with the long-stroke gas system... the gun that comes to mind when I think about a long-stroke is an AK-47. This system has the advantage of being reliable, but is not as controllable as a short stroke or a DI would be, because the center of mass changes during cycling. So the POA is disrupted. I don't think this is much of an issue in semi-auto though. Then you have short-stroke gas system, here the piston is not fixed to the bolt, so it moves separately. FAL, VZ58 and AR-18 are examples of rifles with short-stroke gas systems. Short-stroke is more controllable than long-stroke but IMHO it won't be an issue with semi-auto. Personally if it's for a semi-auto I would go with long-stroke, because it's very reliable, simple and robust.

I will share pictures of the VZ58 short-stroke gas system shortly.

April 19, 2014, 09:02 PM
actually, the AKs reliability has absolutely nothing to do with its gas system, if you look at an AKM (7.62 or 5.45) gas block youll notice the gas vents after only a short distance similar to a short stroke system.. so the AK is essentially a short stroke system as its under pressure from the gas for only that short distance... piston travels with the carrier though but thats all besides the fact.. a true long stroke in which the piston is under pressure until its fully rearward would impact the back of the receiver with quite a force, likely damaging internals

the AKs added reliability is in the mass of its bolt carrier group.. because of the added weight of the BCG it carries more momentum as it travels rearward allowing it be be better at overcoming friction, debris, etc and therefor offers more reliable extraction.. now if the AK was a complete short stroke system like the SKS, and the BCG still had the same mass youd see zero change in reliability

also, efficient cycling isnt the only issue to be concerned with but if the bolt yanks too hard and too fast on the cartridge, it could tear the rim off and leave you with a serious jam

lets face it though, the gas system is just as important to the rifle as the BCG.. true short stroke systems are incredibly snappy as it requires enough force to be placed on the carrier to allow it to cycle on its own.. but im wondering if we could actually achieve a more gentle extraction cycle perhaps with longer stroke (distance from where the piston rests to where the gasses stop pushing it, where the gas vents) you could decrease the pressure of the gas system and smooth out and lighten down that stroke

for the purpose of smoother extraction i had the idea of making sort of a two-strage gas system.. the gas block would be fed by a single gas port in the barrel, but where the gas vents into the gas tube there would be two holes, one small one closer to the barrel that would release a smaller volume of gas to more gently push the carrier forward at a slower rate, and then the upper hole will be the full size one that will carry the energy to send the entire BCG rearward.. and since the gas will have to travel a little bit longer to get to that top hole youve momentarily delayed the second stage

the only downside i see to having a true short stroke system over the AKs basically short stroke but attached piston is that with the AKs setup it means one less spring and another less moving part (the separate piston).. honestly, what is the point of the system the SCAR uses where it has the big chunk of metal almost the full length of the gas system with a tiny little piston head on the front that is separate in the gas block?

thats just a couple ideas i had for the gas system

April 19, 2014, 09:28 PM
Yes, you're right, AK's reliability is because of the BCG mass. But the BCG added weight is in some way related to the gas system. The definition of a long-stroke gas system is that the piston is fixed to the Bolt Carrier.

April 19, 2014, 09:49 PM
I like your idea of a two-stage gas system. Sounds very promising.

April 19, 2014, 09:58 PM
Sorry if I missed this, but what caliber are you considering at this point? I'd assume you're going to use one already in existence rather than build something new, right?

April 19, 2014, 10:00 PM
dcarch, I think he said it was going to be a 7.62x51mm NATO/.308 that could be converted to 5.56

April 19, 2014, 10:15 PM
yeah, alfon99 is right.. im designing it as a .308 winchester / 7.62 nato, but with the provisions (easily changed barrel, bolt and magwell) to convert to any caliber from 9mm up to a 308 and all its derivatives.. so add an AR-15 magwell and 5.56mm barrel and you can use that

so when i design the bolt, magwell opening, ejection port size, etc im focusing on dimensions of the .308

its actually just one of two rifles im working on simultaneously

April 19, 2014, 10:24 PM
One thing we still didn't discuss is wether if it's going to be striker fired or hammer fired.

April 19, 2014, 10:30 PM
Oops. Sorry I forgot you said it was going to be an ar-15 trigger group.

April 19, 2014, 10:33 PM
yeah.. that i havent decided.. it would be fairly simple to just use the AR-15 FCG and go hammer fired in a conventional setup.. but, if we go striker fired id prefer to go bullpup because then i can adopt what the FG-42 used

after the FG-42 bolt was locked, the bolt carrier still had an extra half inch or so of travel.. the op rod of the FG-42 was held by the trigger and the bolt carrier held the firing pin.. when the trigger was released it allowed the extra half inch of travel under power of the mainspring to fire off that round.. which enabled a strker fired system that included no extra springs and could easily be operated from the front of the rifle (remember, the FG-42 has a side magazine so its action was much further back than on a conventional rifle.. it was damn near a bullpup in its own right

anyway.. that would mean zero trigger linkage, no added parts, and you wouldnt even need a firing pin or striker spring if you do it right which could really lighten up the rifle and aid in dependability if its done right

if im going with an improved G43 type locking system, i could attach the firing pin to the cam block that spreads the locking lugs and have the bolt carrier catch after the rifle is fully locked (so still a closed bolt rifle) but still allow that cam block to travel another quarter inch or so when the op rod is released by the trigger

so... bullpup with an FG42 type semi auto fire control group.. or conventional with an AR-15 trigger pack?.. also, the FG42 system could be adopted to a conventional rifle simply be adding an extension to that cam block towards the rear and have that lock to the trigger/disconnector

April 19, 2014, 10:46 PM
I say go hammer fired in a conventional setup, with an AR-15 trigger group.

April 19, 2014, 11:15 PM
As far as ergonomics it would be nice to save a lot of stuff from the ar 15 like the mag release, safety, and the barrel being in line with the stock unlike the AK, Thompson see, etc. It would be cool to see features like bottom ejecting with a charging handle mounted on the left side of the receiver. And being bottom ejecting, it wouldn't be terribly hard to switch over to the right side for left handed shooters.

April 19, 2014, 11:31 PM
Good thread. I wanted to dump a few thoughts and comments here.

On the flapper bolt, I was almost sure these got a bad rap with the G43, but after seeing that .338 lapua semi-auto in G&A shooting sub MOA, it sounds promising (at least with CNC precision).

On the idea of a 556 tube gun, how about designing a one-piece tube bolt that has a raceway cut and rotates on a reciever mounted pin? i.e. instead of a bolt that rotates inside the carrier, have a bolt that rotates inside the tubular reciever. To combat friction, a washer could be mated to the back of the bolt while a coil spring pushes the bolt forward agains the pin. Of course, careful use of cutaways would have to be cut so the hammer wouldn't be obstructed. So perhaps this could be a blowback rifle with rotating bolt delay...with no gas system other than that directed a the bolt face.

Another strange idea I had: rotational locking...of the piston instead of the bolt. You could use directed gas to rotate a piston, or just push a cam/raceway oprod in a linear direction. My point is the unlocking would be done either near the gas block or front trunion, or hell, even inside the carrier. It throws aside the notion that the bolt itself should rotate to lock/unlock.

How about a spin on the ZM/Para TTR concept (minus the DI)? Just replace the gas key with an extended cylinder that could also act as a carrier guide. So essentially a piston AR upper with half a DI gas tube that injects gas into a female piston counterpart (i.e. an extended gas key with no gas flow to the bolt). Then work out the action spring to your tastes.

Benelli ARGOS gas system is pretty neat, presumably reliable, and seldom used. I like the idea of an annular piston (if anyone has a good pic of one I'd like to see it)

April 19, 2014, 11:53 PM
if the front of the piston is what locks, then what unlocks that?.. also, the bolt cant just turn on a rail inside the receiver because then it would only be able to lock on an angle which wouldnt be locked at all, in fact, what you just described is a screw-delayed blowback.. which if done right, say the bolt had the proper weight and you had the proper pitch for the interrupted threads in the chamber would work

with a screw delayed blowback as the gas pushes backwards against pressure in the chamber, the bolt, which is on an angled thread will then turn slowly before it reaches the point where the threads are interrupted, releasing the bolt for full cycling.. something could theoretically be possible to put a cam surface on the bolt body itself.. a groove that begins straight and as it gets closer to the tail of the bolt the pitch rapidly sharpens.. then have a knob riveted into the receiver that will sit in that groove.. which in theory could be an incredibly cheap way to make a 5.56mm tube gun capable of handling the pressures of a 5.56

as for the gas system you mentioned at the bottom of your post are you suggesting using sort of like a hollowed out tube attached to the bolt carrier that will extend beyond the trunnion, and then have a direct impinged tube go inside of that?.. drill a side hole in the gas tube so when the sleeve for the DI system uncovers it itll vent the gasses.. it would work i think and keep fowling out of the inside of the receiver


the other design im working on which hasnt been discussed here yet is basically going to focus on being the simplest rifle you can possibly get.. it wont have a top rail, wont have quick caliber changes, or interchangeable furniture.. this one will be a tube, a 5.56mm barrel likely pressed and pinned into the trunnion, and have no gas system, so it will either be delayed blowback (the screw-delayed blowback maybe) or be recoil-operated which if you look at the barrett M82 and the johnson 1941 rifle can still be accurate.. and i envision this second desgin since its being made out of a tube to look something like a scaled-down barrett M82 rifle with the buttstock fitting inside the rear of the tube and the forearm being a vented extension of the receiver

April 20, 2014, 02:28 AM
so anyway the question with the gas system is.. attach the gas piston to eliminate the need for an extra spring, or go short stroke but still make sure the BCG has sufficient mass to ensure reliability?

April 20, 2014, 03:53 AM
Maybe the latter is better. SCAR style.

I think you got the gist of my forementioned ideas. To clarify on the tube gun idea, 'screw delayed' isn't too bad description for what I called blowback rotating bolt delayed. That 'groove' is called a raceway IIRC, and that 'knob' is what what I refered to as a pin.

And as for the ZM-ish spin-off, you're spot on.

April 20, 2014, 04:11 AM
what id like to do is what the AUG does attach the guide rods to the bolt carrier.. and have these attached to the front of the carrier, not the rear.. one of the guide rods will have a piston head and the other one will be used by the forward mounted non reciprocating charging handle

the recoil springs appear to be inside those rods, with two spikes on the back of the receiver that go through the bolt carrier and pushes against the springs to push the bolt back forward.. you can see the bolt with the rods below.. benefit of this is a much shorter action (no springs behind the bolt) and maybe make the functions of the two rods reversible to switch the charging handle to the other side and switch the piston to make it ambidextrous

im still not opposed to just using a conventional single piston system with internal receiver rails, but i think the AUG idea is a very good one as not only does it do everything i mentioned above but if you went that route you wouldnt need internal receiver rails

April 20, 2014, 12:05 PM
im going with gas system im going to base on the M-14 gas system.. it has a longer stroke (the length in which gas impinges upon the gas piston).. which means the gas pushes the piston for a longer distance before venting, this allows you to use lower pressure gas as you have more time to build enough energy to cycle the action... this should help to reduce recoil, and be gentler on the brass being extracted

however, there wont be any long op-rod on it like on M1 rifles.. itll have more like an SVT gas piston which will be easier for caliber changes because the gas system can be built into the barrel assembly.. shorter gas pistons for shorter barrels for example.. gas systems can be individually be tuned to the barrel and cartridge

April 21, 2014, 02:11 AM

April 22, 2014, 06:55 AM
what do you guys think about this idea?. what if i borrowed a lot of design elements of the FG-42.. side magazine which balanced much better than a front mag, allows the bolt carrier and piston to be on the bottom which allows the bore to be much higher, so scopes and sights will be closer to the bore and the bore will be better in line with the shoulder

also, i could very, very easily mag an FG-42-like bolt by using interchangeable savage 10 bolt heads and a pipe for the bolt body that the bolt head mounts into


what would be different VS the actual FG-42 is this one will be simplified, using higher quality metals, will be a bit smaller (no 8mm) be multicaliber with easy change barrels, interchangeable bolt heads and interchangeable magwell

it would also be ambidextrous.. a savage 10 bolt head can be put in upside down, ejecting out the opposite side and the magwell and a side plate for the ejection port will have the same footprint, so they can be reversed.. this also allows more complex magazine wells to be machined out of lighter materials like aluminum that could include features like a port buffer and a dust cover

by using bolt which locks into the barrel or barrel extension it allows the receiver to be sheet metal or tube steel, allows the front trunnion to be aluminum, combine that with aluminum or polymer magwell, aluminum ejection port, the fabrication of trigger "packs" by using a cage for the trigger parts the lower can then be injection moulded, aluminum, sheet metal, or possibly even 3D printed which would bring the overall weight way down from the original FG-42

and with some design changes in the barrel, BCG, gas system it would also be more accurate and more reliable than the original FG.. the only design details that would be the same, realistically will be the bolt design and the overall shape of the receiver/rifle

so.. what do you think about this idea?

April 22, 2014, 07:42 AM

ar-15 bolt action upper

April 22, 2014, 07:44 AM
umm, what was the point of that?.. im designing a semi automatic

April 23, 2014, 12:03 AM
VZ58, DP28, FG42... stay still, darn it! :D Just kidding, I can tell you're still in the spaghetti-throwing portion of the design phase, where lots of ideas get thrown around really fast. My skorparev went from recoil-operated tilt-barrel, to tilting telescoped bolt, to gas operated tilted bolt for a really long time, to (briefly) VZ58-style tilting locking piece, and finally to the Degtyarov system with a long-stroke barrel centric square-profile piston (for now). A word of advice; you will chase fewer rabbits down blind alleys if you keep track of why you should choose one design over others (strength, ease of manufacture, safety, reliability) and firm up your desired feature-set as best you can.

Feature set as I understand it so far:
-Locked breech (any particular reason delayed blowbacks are off the table?)
-Gas operated (long stroke fixed piston, from the sound of it. Any reason recoil-op systems are off the table?)
-Rotating bolt head (repurposed Savage bolt head)
-Mag fed (max size 308-ish envelope)
-Grip-centered weight distribution (be sure you aren't compromising ergos with the side mag just to satisfy this condition, when you can probably achieve it through other means)
-Low profile upper (which is why I assume you desire the piston alongside the barrel, but remember you'll still have to lift the sights up unless your stock is dropped a bunch)
-Lightweight construction (might I suggest aluminum G3 mags or paratrooper FAL mags)
-Multi-caliber capability (bolt/barrel are swappable)
-Multi-magazine capability (magwell is swappable)
-Overall modularity (modularity is highly over-valued on a one-off custom gun, unless you have industry/military backing to take advantage of it. AR's get re-configured because there's lots of parts available and it is therefore easy; each change on your custom gun will be a monumental effort to design and build extremely expensive parts)
-Accuracy (sounds like you want the thing DMR-rated, as a minimum, so let's say 1-2 MOA?)

Try to focus on why one operating system vs. another helps you or hurts you in satisfying this feature set, and try your best to not mess with the features your are going for without good reason. Design is hard enough when you aren't designing to a moving target; you'll just end up churning forever and accomplishing nothing.


April 23, 2014, 12:45 AM
One thing we still didn't discuss is wether if it's going to be striker fired or hammer fired.
There's also merit in a linear hammer like the VZ-58 or Norinco Type 97.

April 23, 2014, 03:46 AM
well, to answer barnbwts questions.. reason i havent, and probably wont consider delayed blowback is what it takes to flute a chamber, how partially extracting during the delay process tens to blow out the shoulder of the case shortening reloading life of the brass, and delayed blowbacks tend to be very ammo-picky even within the same caliber, no idea how having something with the flexibility of using multiple calibers would work with a delayed blowback

if i go gas operated i decided i want something more like the M-14 system, with the longer stroke (distance the piston travels under pressure as the M14 gas tube vents out further back), this allows softer recoil and extraction as it uses lower pressure over a longer distance.. but id want more like an FAL short stroke piston because then you can use different piston lengths for different calibers and barrel lengths

i think i do want to go rotating bolt head to be honest.. it really is a lot easier than roller and flapper locking, able to buy savage bolt heads but if i didnt go that route id go with the triangular bolt because you could lathe out the rough shape and file the edges down to make that 3-lug bolt

as for making it more modular.. when you think about it, it actually makes construction a lot easier too.. if your magwell bolts on, and your bolt head (say you use the savage 10 bolts) it allows you to have these parts made separately and screwed or pinned on later.. means theres much less manufacturing required on the bolt and the receiver and it also allows some parts to be aluminum such as the magwell which decreases the overall weight by not having to weld on a steel one.. or even a polymer injection moulded magwell could be possible.. with the bolt locking in the barrel you could also go with a lighter receiver and possibly even an aluminum trunion.. so all the features that make it modular also makes it lighter weight and easier to construct, and if someone is making the rifle themselves, if they mess up on one part, say the magwell they dont have to scrap the entire receiver and start over

as for the side mag.. it has some pretty big benefits, longer barrel in a shorter package, longer recoil track over a bullpup, conventional trigger packs could still possibly be used without linkage, much easier to operate and reload when prone, and if the magwell and the plate on the opposite side with the ejection port are swappable then its ambidextrous with only needing to cut out two sides of the receiver, and not three (one for the magwell plus two for the ejection port).. ergonomics while carrying are the only issue.. with the magazines being p-mag or polymer FAL mags and the magwell being injection moulded or aluminum, there wont be much of a balance issue.. the only time ergos come into play is when slung.. but i believe if a right handed shooter attaches the sling to the right side of the rifle.. with a three-point sling system you could have it lay across your chest or back on its right side, and easily shoulder it with a quick adjustment

if the side mag rifle cannot be easily and comfortably carried then id be more inclined to go bullpup.. your front arm takes far, far longer to get tired, you get a longer and more accurate barrel for the length, and if you used some kind of an op-rod on the bolt carrier to allow the bolt carrier to also be used as a striker in the FG-42 fashion, you could also eliminate all linkages in the trigger mechanism and your trigger would be no more stiff or long than firing something from an open bolt (though this rifle will fire from the closed and not be too easy to modify to an open bolt), and if the carrier holds the striker, thats one spring needed for both

April 23, 2014, 09:05 AM
ive actually been giving short-recoil operated a lot of consideration lately.. i know people are going to turn their nose up at it and ask how can a recoil operated rifle be accurate?.. well, from what i could gather the 1941 johnsons were as accurate as garands firing the same ammo... the answer to making a short-recoil operated rifle accurate lies in the 1941 johnson.. and id imagine with the tolerances we could build into a rifle with todays far more precise machinery, we could adopt some of the things johnson used for accurate and make a pretty accurate short recoil operated rifle

if i were to build a short recoil operated rifle.. im probably going to go with round or octagonal tube steel.. extend the receiver section out over the barrel, drill and vent it, rails could be added later and in the end of that tube would be the block that the barrel rests against when its fully forward.. tapered to match the barrel, i believe the block in the johnson was chrome lined to fine tune the fit with the barrel.. then you could just slide the stock into the butt of the tube, pin that in and have an assembled rifle that would look somewhat like a scaled down barrett

but my question is this.. can a recoil operated rifle be suitable for a multi-caliber platform? going from a .308 down to a .223 is a pretty big jump... how would you tune individual barrel assemblies to function in the same rifle without serious reliability issues?

perhaps its a good idea to run with.. but only in a single-caliber platform.. but i guess if the upper is just a piece of tube steel.. you could weld or rivet a magazine well to it and have the upper assembly contain everything for a particular caliber and just swap out the grip frame / trigger group.. likely the upper assembly would end up being called the rifle, but at the cost of a piece of tube steel and a cheap magwell, who cares?

however... perhaps you could fine-tune the rifles with muzzle brakes.. the bigger calibers would have muzzle brakes designed to reduce more recoil and deliver less enegy backwards while the smaller calibers like 5.56mm could have muzzle device that doesnt eliminate the recoil that effects the barrel, or if need be could use something like a krinkov muzzle brake the generate more rearward energy into the barrel for cycling

April 23, 2014, 10:51 PM
"probably wont consider delayed blowback is what it takes to flute a chamber"
Why, you use a fluted reamer, of course :D

Here's a short recoil action I just found about today; the 14.5mm KPV heavy machine gun. Obviously yours would be smaller (:D), but it's a rotating bolt short recoil op gun with gas assist (so some flexibility for loads/barrels/cartridge power levels)

"the 1941 johnsons were as accurate as garands firing the same ammo"
Yeah, but is that really saying a lot? Neither were 1MOA guns, which is what you'd want to at least aim (pun) for if you hope for an accurized design. Accurization wasn't really the chief consideration during the rifle trials (a consideration, yes, but not a primary one for the job it was meant for)

"how would you tune individual barrel assemblies to function in the same rifle without serious reliability issues?"
You primarily operate the gun by muzzle-boost rather than straight recoil. That way the booster can be modulated to work with a wider array of rounds, but I still don't think you'd have luck getting a 9mm to operate a 308 capable gun (I'd just use a straight blowback bolt for the little pistol-cal rounds like they do AR uppers). The trouble here is that the ATF will at some point declare your booster a silencer (and only The Shadow knows where that distinction lies...)

"as for the side mag.. it has some pretty big benefits, longer barrel in a shorter package, longer recoil track over a bullpup, conventional trigger packs could still possibly be used without linkage, much easier to operate and reload when prone, and if the magwell and the plate on the opposite side with the ejection port are swappable then its ambidextrous with only needing to cut out two sides of the receiver, and not three (one for the magwell plus two for the ejection port).. ergonomics while carrying are the only issue"
Couple thoughts on the mag setup;
-the pros you list are true for top-mounted magazine setups, but none of the downsides. A Calico/Bizon helical mag up top would keep plenty of ammo on hand (even long rifle rounds, unlike the PS90 mag), and the mag bodies would be the same for all calibers (the internal fins would be the same, and only the helix would vary), or if you are feeling ballzey, a protruding BREN or Madsen like magazine has certain benefits (and costs) as well. Namely they make drum/pan/belt conversions easier (as do bottom magwells)
-Another option would be a grip-well; only instead of attempting to wrap you palm around a 308 box mag (:D) you keep your thumb on the strong side and only wrap you palm around the front of the grip. Radical departure, but would get extremely-long mags in the same package as a bullpup while having slightly better balance and (maybe) ergonomics of mag changes. Find a way to load them from the top like stripper clips and you'd have all your benefits and none of the costs.
-If a side magazine is what you end up running with, consider making the gun automatically ambidextrous. When the mag is latched on one side, the latch automatically shifts a linkage that causes one of two extractors to act as an ejector (see the ARX160 by BRNO), and if you're really clever, pops the charging handle out the other side of the gun (like the ARX160 does with manual manipulation). The gun could freely be fired either way with no other action by the user, which remedies all issues except for the awkward carry. On that note, I'd suggest a 'carry magazine' which only holds a few rounds and is flush with the (also flush) magwell opening, and doubles as a dust cover. Not an awesome solution, but a solution. Either that, or an L-shaped magazine that drops down alongside the weapon to at least minimize the snagging annoyance. If the receiver is wide enough, the bend of the L would be flush with the sides.
-Be sure to make the magwell flush with the gun; good for carry, and you'll have extra width to work with seeing as you have guide rods/pistons located to the sides of the barrel. Your receiver will be fat and short, as opposed to the AR's tall and skinny; take advantage of that where you can.

"if you used some kind of an op-rod on the bolt carrier to allow the bolt carrier to also be used as a striker in the FG-42 fashion, you could also eliminate all linkages in the trigger mechanism and your trigger would be no more stiff or long than firing something from an open bolt"
That's because you'd be firing from an open bolt.;) The open bolt regs aren't there (just) because the ATF is a big meanie, it's because what you describe is laughably simple to convert to full auto; just remove the sear and it's "go" time, same as any other open bolt. And that's what the Bureau seeks to prevent by requiring a firing system independent of the firearm action, so that if the FCG is removed, you get hammer/striker follow and no ignition instead of fun times in the Federal P.

Besides, you can do better than that, anyway. Without the huge running start a full-length open bolt has, you'd need a very strong spring to kick the carrier the last little bit of its travel fast enough to ignite a primer. 90% of the charm of open bolts is they can be cocked easily, and you'd lose that. You'd still get the heavy/awful trigger and 'open bolt lurch' and long lock time, but at least an out of battery slamfire would be less likely. You get all the benefits and little cost besides a small bit of extra complexity if you go with a hammer or striker setup (which you wouldn't even be designing if you use an existing one)

April 24, 2014, 03:19 AM
well, to respond to some of those things mentioned.. cant really go with a helical magazine because that would require fabrication of an all new magazine and restrict the rifle only to that.. the idea is to use pre-existing magazines, so that really wouldnt work.. besides, helicals are mechanically more complex, likely less reliable.. also, top magazines tend to block your line of sight.. even if theyre on the side you tend to lose peripheral vision on that side which is never a good thing, so i think id limit my choices to either a side mag or full bullup

also, id go with enblocs long before id go with stripper clips because of how much faster it is to reload an enbloc, theyre almost as cheap, and they eject themselves.. i mean, its not a bad idea if you think about it.. you could possibly even have a single magazine body and simply use an enblock with thicker walls on it to hold smaller cartridges like 5.56mm.. wonder if you could design one that could hold 20 rounds of .308?.. then the magazine body would be on the opposite side in which you load it so youd never have to worry about it pressing against your body

i think id stick with interchangeable magwells.. i wonder though, has anyone come out with a good casket magazine for .308?.. having quad stack magazines would make the side magazine idea even better as it would keep the side to side balance much closer to the rifle

also, as to how the FG-42 uses the carrier as the striker, if im not mistaken the semi-automatic reproduction FG-42s do exactly this as done on the original but its not an open bolt because the bolt is fully locked into the rifle before the carrier even catches.. and has ATF approval.. as to it being easily made full auto by removing the sear or disconnector?.. which semi automatic rifle isnt?.. you hold back that catch in any rifle and its going to fire full auto, and it couldnt actually be converted to open bolt without some additional welding, machining, and re-heat treating which goes well beyond the means of a simple conversion.. you could just as easily convert an AR-15 to open bolt.. also, i said the trigger pull wouldnt feel any worse.. the way id actually set up the trigger would be to try to see if i could use an AR-15 trigger group less the hammer but i doubt that would work

i like the better balance of something with a side mag or in a bullpup configuration, i like having a more compact package and still have a longer barrel and better accuracy.. downsides to a bullpup though is the triggers ALWAYS suck.. using a striker though instead of a hammer would fix the issues and offer the best of both. another point to note though is that i when i build mine, i will be going for accuracy too.. light trigger pull, longer barrel say 18" in the 308.. all free-floating too except for the gas block.. even a top rail that would allow the installation of scopes.. so.. having the side magazine making it easier to shoot prone on a bipod could be very useful in achieving a 600-800 yard semi automatic


as for the recoil operation, i was reading about some of the people owning the johnson 1941s and with average ammo they were getting around 2 MOA which is easily military accurate.. better than the average AK, heck, a bit better than many mosin nagant bolt actions (lets face it, most mosins were made in a hurry and therefor shoot rather poorly) and i think when you throw into it some modern CNC machining i could make one just as accurate.. im not sure if id go multi-caliber on this design though.. as i mentioned in one of my above posts i could use .308 muzzle brakes designed to reduce recoil, and .223 brakes designed to increase more rearward energy such as the krink style break.. but is it necessary?.. is it worth the added problems one may have fine tuning each barrel... each fine tuning measure requiring the fabrication of an entirely new muzzle brake to do so?.. and when the receiver itself is just a pipe with a magwell welded to it?

it seems like for the recoil operated rifle i should probably come up with two separate designs, one for .308 length cartridges, the other one for .223 length cartridges.. each one using a fixed, welded on likely folded sheet metal magwell.. could still use interchangeable savage bolt heads. but interchangeability isnt important in this case.. and you might as well just use a bolt design that was brutally simple to fabricate like the triangular lug which you could lathe out, then file down the sides and be done with it.. since theres no gas block, savage 10 barrels would be easiest since theres no need to shape it for installation of a gas block.. if someone wants a left handed version simply cut out the groove in the bolt in another location so it can eject to the left instead and put the charging handle wherever you want it

April 24, 2014, 04:13 AM
so.. heres what i have so far

design 1: gas operated rotating bolt

short-stroke gas piston with a longer travel for smoother recoil and extraction

multicaliber with interchangeable magwell, reversible bolt heads

side magazine or bullpup

magwell and ejection port can be swapped on side-mag, or two ejection ports for the bullpup

entirely ambidextrous

non-reciprocating charging handle likely positioned in the top under the rail which will be heightened a bit to clear it (think G36C rail)


design 2: short-recoil rotating bolt

no gas system, easier to clean

carrier will be a simple piece of tube steel

not multicaliber, but easy enough to build additional rifles for different size cartridges

stamped magwell welded on, or machined aluminum or polymer magwell riveted on

bullpup or front magazine.. end result would look like an M95 or M82 barrett

simple to fabricate triangular bolt with "ak-style" extractor

id like this design to use a frame-mounted extractor.. but this seems like it would be contradictory to simple upper receiver and bolt construction unless i could design an extractor on a pivot that pops up as the carrier rides over the tail side of it... possibly installed in the trigger housing (any ideas here would be appreciated) for the sake of simplicity ill probably just stick with a bolt mounded plunger-style ejector since you realistically only need a drill press to make this

i wonder if you could somehow have a long eye relief scope or red dot sight on a rail mounted on top of a forward, reciprocating section of the receiver.. if the scope or red dot could handle recoiling with the barrel youd have absolutely perfect accuracy since it would remind perfectly in-line with the barrel at all times, even if the barrel itself didnt perfectly return to zero


so.. i will be designing both of these... and thats what i have so far on the two.. feel free to discuss either one.. no reason i cant make one of each.. im leaning towards the side mag for the gas operated and bullpup for the short recoil.. but as you can see im still open about a few things

April 24, 2014, 06:19 AM
i have this other idea worth throwing out there... since the top rifle will likely be a side mag with the gas system under the barrel..or if it goes to a bullpup it will use a carrier like a steyre AUG, again with the bolt being on the top side of the carrier.. it frees up the top surface of the bolt that i could easily cut a cam surface for an AR-10 bolt and it compliments this other idea ive been having for the gas system

for the gas system, ive been thinking of mounting a short gas tube to the front of the trunnion.. have this short extension contain a short-length, short strike gas piston and spring, it would realistically only need to extend maybe two inches out of the front of the trunnion... this way you can use an AR-10 or AR-15 gas block and extend the gas tube back to the front of the trunnion where the piston is at.. this allows you to have different length gas systems and only require you to cut a simple AR-15 style gas tube to length

downside to using AR-10 bolts and barrels is they dont make a .223 option and i dont think an AR-15 barrel would even fit into an AR-10 receiver to justify designing a carrier that could use either bolt.. so youd need to get an AR-10 barrel extension, chamber it for .223, then weld up the bolt face and tip of the extractor claw, machine these for the .223 bolt face and re-heat treat.. so it might still be easier in the end to use the savage 10 bolt face, a pipe for a bolt body for it to mount to and just have to lathe out the required barrel contours from a blank

but its an idea worth considering as an alternative to using a savage bolt head which is available in bolt faces for every caliber.. and im still not opposed to using savage barrels either.. just need to realize youd have to lathe an untapered section out for the gas block to sit on (or ream a taper into the gas block) and couldnt use a receiver extension for the forearm because then you couldnt get the wrench in to tighten the barrel extension, and using savage barrels would require a steel trunnion

April 29, 2014, 06:12 PM
well.. ive made some significant progress here.. ive designed much of the upper.. the receiver i seem to be settling with is a piece of square tube steel but a strip down the center of the top is removed.. allowing the remaining lips to add as rails, like on an AK receiver.. then theres a dust cover thats slid on over top.. but slid on like an FAL dust cover.. in fact, removal of the dust cover isnt even necessary for a field strip.. so it can even be welded on as a solid receiver.. but i like the option of being able to remove it for easy access to the internals

so far ive just modeled a basic aR10 magwell, just a simple one thats not even final, im going to make it much longer, and its a bolt-on magwell.. could easily fab an FN FAL magwell that would fit in place of this one.. bolt one off, bolt the other one on.. and ill be designing an AR-15 magwell for it later.. the tab where the bolts go into on the back side of the AR-15 magwell will be extended to make up for the smaller length.. magwell is black because i set this one to be made of injection moulded polymer (add about .25lbs for aluminum)

i still need to work on the sheet metal box for the lower, itll use an AR-15 buffer tube and stock, though the buffer tube wont function as such, itll just be to hold the stock.. also going with a triangular bolt and something more along the lines of the M14 gas system.. you can see the op-rod attached to the bolt carrier.. there will be an adjustable gas plug on the front of the gas block, and a short-stroke piston in the gas tube

you can see my rifle starting to take shape.. when its finished i estimate, and im shooting for roughly 8lbs, which is what an FN SCAR-H weighs

when this is finish, i predict it will have the weight of a SCAR-H, interchangeable magwells, easy change barrel, so in all simple caliber changes, and likely lower felt recoil than a SCAR-H due to the stock also being in line with the bore but also using a longer stroker lower pressure gas system

at this stage it is currently 4.75lbs and all its missing is the short-stroke piston, the gas plug, i need to make a couple small tweaks to the bolt itself and the handguard and then the ENTIRE upper assembly is finished


required skills to assemble the rifle from a parts kit.. less receiver would be simply cutting a strip in the receiver to act as the rails, cutting the magwell, and drilling out some holes for the trunnion rivets.. due to the bolt locking in the barrel the trunnion is to be made of aluminum to save weight, and it will use an off the shelf AR-15 FCG

this is it so far

April 29, 2014, 11:37 PM
Cool, it's looking a lot like a G36 so far :D. If I may be so bold as to ask; why the AR buffer tube constraint? The tube itself is the product of a design compromise and arguably the weakest point of the AR platform. I can sort of understand a desire for something you can easily interface with, but a 'blank' back end capable of being adapted to use AR, AK, FAL, or any other stock would be far more flexible, would probably take up less room (your bolt carrier body could get much smaller), and would be capable of accepting folding stocks (I like them over collapsibles, so do some other folks)

Have you figured out how big of a bolt thrust your bolt lugs can carry, yet? That will put a top-end on the cartridge power you're going for, which will put a limit on how big of mags/cartridges the magazine well would need to be adaptable to, and how much bolt throw you need to accommodate the longest. The recoil attendant your top-level cartridge will also drive how beefy the rest of the gun needs to be.

As far as receiver construction, there's some cool threads elsewhere about a project called the AK42 (or was it MG47?). Basically, it was an AK action flipped upside down in a new receiver and converted to belt-fed with an MG42 topcover. The receiver was two stacked square tubes with their mating face milled away and then welded together to form a BREN-like railed carrier tube.


April 30, 2014, 08:48 AM
never heard of it, but i did find an image when i searched MG47 so i think thats it

as for the stock what i was planning to do was to put a hinge mechanism on it that would hold an AR-15 buffer tube for the stock selection.. what do you think about the ACE modular trunnion AK builders use to replace their original trunnion to allow the plethora of ace modular add-ons for their stocks?.. i could easily design something compatible

May 1, 2014, 10:30 PM
at any rate.. heres a photo of the rifle mostly done.. still need to finish up and tweak a few things.. not sure i 100% love the way the magwell hooks into where the lower receiver pivots for field stripping and havent 100% arrives to a decision on how the barrel will attach, im honestly leaning towards an interrupted thread and something to secure it in place like a lever or a detent

anyway, below is the photo.. and i did some math on this to calculate just how much force my bolt could handle, but i didnt just measure how much force my bolt could handle.. i made sure to measure the maximum allowable bolt thrust of the section of the bolt that actually contacts the locking surfaces in the barrel extension.. after crunching all the numbers this is what i came up with for my current bolt design

maximum PSI of the metal surfaces (using 4140 steel hardened to a rockwell hardness of 49 (its low, i know) was 42,728PSI.. with the surface area of the cross section of my bolt lugs where they contact the locking surfaces in the barrel, it gives me a maximum bolt thrust of 17,305 pounds.. this would make my bolt capable of 338-lapua

for anyone wishing to run the math themself.. the "arc length" though in this case its a straight edge where it contacts the barrel extension is 0.361" and the axial length of these surfaces front to back is .375" and there are three lugs

im thinking of reducing the diameter of my bolt and my locking lugs.. the capability of .338 lapua is overkill for a rifle i cant possibly conceive ever being chambered in anything with greater bolt thrust than a .308.. not even if i made an extended version of this rifle to express my affection for the 8mm mauser round

so yeah, im at a point in this design where the mechanics are all there and now i need to start getting serious about things like metallurgy as well as shaving off some unnecessary weight.. and prior to these weight reductions, with all components already added to the rifle im at exactly 8lbs for the total weight of the rifle, after weight reductions we'll be looking at a 7.5-7.75lb rifle with a 16" barrel.. and that is an AR-10 magwell with an AR-15 mag release.. so aftermarket "bullet buttons" can be installed for cali people

oh, and im looking for a gas system that will be multi-caliber, multi barrel length friendly.. so what i intend to do is shorten the oprod and drill a pocket in the face of the oprod to act like a gas key on an AR-15.. at which point id like to be able to use .750" AR-15 gas blocks and gas tube with that gas tube going inside the pocket in the front of the shortened oprod.. what this will do is allow me to have different length gas systems that can easily be adjusted simply by trimming the gas tube that directs gas from the gas block to the shortened op rod.. this also keeps more mass rearward for a better balanced rifle

May 1, 2014, 11:38 PM
Lookin' good so far. I have one of those ACE adaptors I plan on using for my AR70 one of these days (a cool design to draw inspiration from for your swappable magwells, btw ;) ). The ACE things are well made, but they made the fatal error of using bead-blasted anodized aluminum for the bearing surfaces. Aluminum sucks as a moving bearing surface for a number of reasons, so long story short, the ACE folders are almost comically hard to open/close. Doesn't help that they use automotive valve springs to tension the latch ;). Still, there's probably nothing better that's as universal to flat-backed receivers out there :cool:

Have you changed the bolt head from when you posted pics earlier? The lug diameter is large enough that it looks like it could probably handle gun-level loads (usually when I see the concept of polygonal bolts pitched, the flats are tangent to the shaft, leaving very little meat behind). I would also suggest you make the flats into concave grooves as close to tangent with the bolt shaft as possible, with a standard ball-mill size radius. This will increase the space efficiency of your lugs, and will be just as easy to mill as a flat face (use ball mill instead of end mill) :cool:

Were your stress calculations for ultimate, yield, or fatigue conditions? You don't want to operate at the yield point, or your headspace will go all wobbly in a handful of shots (your conservative hardness estimate helps you here, but a S-N curve for fatigue in steels is a better guide for finding where you wish to operate)

Secondly, was the failure you were checking for shear or contact load at the lugs? Bending and compression are obviously not the critical numbers for such a short 'beam' as a bolt lug. Shear probably won't be either, unless your bolt lugs are really short front to back. The contact load was always what ate me alive when I'd design bolt heads; that's why 1911's have so many barrel lugs and why a skinny interrupted-thread bolt needs so many threads. Spreading the load out enough that it wouldn't peen stuff seems to be the driving factor for things like bolt diameter and receiver(extension) strength.


May 2, 2014, 12:08 AM
i tested the shear of the locking lugs.. but not the entire locking lugs.. but the tip along the line that contacts with the locking surfaces within the barrel.. and yes its the same bolt you see in the carrier above.. so youre suggestion of removing some material on the flat edges of the bolt based on common endmill sizes is a pretty good idea so ill see how that works out

as for the stock, im really leaning towards having the rear of the lower set up for the buffer tube, with a side folding buffer tube adapter.. so you can have a fixed or folding stock.. id like to use a buffer tube with a door in the front of it so while the stock is folded you can open up the storage inside the buffer tube which will likely contain things like a cleaning kit

now heres an issue im having right now.. the rifle ejects at an angle 30 degrees above horizontal.. this places the ejection towards the bottom edge of the interior rails, where you see the ejection port now it removes a chunk of the internal receiver rails, you can see the groove in the bolt carrier that rides on these rails.. i dont like this because i dont want dirt, dust, and debris to get trapped into that groove and then get pulled inside the rifle when firing and i cant move the rails because this upper is a piece of 1.25" square tube steel with the top edge removed to make the rails and a dust cover over this

so anyway, im probably going to change the carrier around a bit to save weight (currently the carrier + oprod weighs 1.2lbs vs the 1lb for the AK carrier+piston) and i think id like to get the weight down to about 1lb.. also i think im going to design an ejector thatll eject at a lower angle


on the order of the receiver the reason i went with the receiver you see is because its incredibly simple to fabricate and doesnt require welding, and the ability to remove the dust cover allows easy access to work on the internals while the dust cover doesnt have to be removed for field stripping and disassembly it allows a full length top rail...

but other ways i can design this receiver is a piece of rectangular tube steel or a piece of long D tube steel which in either case would require using a couple steel angles welded to the inside for the rails

of those receiver options, what do you think would be best?

May 2, 2014, 12:39 AM
yeah, im not going to change the bolt.. the bolt face as it stands allows a maximum rim diameter of 13.6mm with enough lug to handle 17,000 pounds.. im looking for this to be a bolt i can use for other rifles as well including this other side project im working on of a straight pull bolt action.. if i can use the same bolt and the same barrels it'll allow said straight pull bolt action to be a .300 winchester magnum.. my idea is to make interchangeable bolt heads similar to what the savage 10 rifles use but in a more flexible 3-lug design.. the bolt body itself may be little more than a pipe

due to the design of my bolt carrier, its not final, not even close.. that was just a rough sketch to get something put together to start getting a better idea of the mechanics of this, i still have a lot of changes to make on that and hopefully make it less top heavy because i want more of the recoiling mass to be closer to the bore and in line with the bore and stock.. low recoil is a goal.. i want to design a 308 rifle thats going to be very accurate, very reliable, and comfortable for even smaller size people to shoot.. so a lot of thought has to go into finding a good muzzle brake thatll reduce even more recoil but still be comfortable enough to shoot without ear protection

it looks like im going to begin working on a prototype soon.. the decision im facing now is do i keep this a square tube steel receiver with half a piece of round tube steel for a dust cover (which can even be welded on since its removal is not necessary for disassembling the rifle).. or do i go back to my original idea of a piece of rectangular tube steel or long D tube steel and plug weld rails to the inside of it

May 2, 2014, 06:15 PM
"I'm looking for this to be a bolt i can use for other rifles as well including this other side project im working on of a straight pull bolt action"

Hmmm...rotating bolt...camming flutes on bolt head shank...straight pull bolt action... ever mess with a Steyr M95, before? The bolt heads are almost exactly what you are describing, albeit two big Mauser lugs rather than three.

As far as bolt heads, be sure, too, to check out the Thompson Center Dimension series (I'd forgotten about until just now). Ugly-assed rifle, brilliant concept. It's a three (square) lug bolt head that locks into a barrel-extension like an AR. The receiver is basically a threaded tube with a keying feature to keep the bolt head aligned as it enters the barrel (a gas-op wouldn't even need that). Just like the AR, the barrels/bolts can be swapped out readily, and are supposed to be available in a ton of sizes (probably not as many as Savage since it hasn't been out as long, but there's quite a few already). I think buying a Dimension bolt/barrel to build a semi-auto off of would be a pretty cool concept (they all have the same critical exterior dimensions so as to fit in the stocks, etc.) and might actually make more sense than trying to get a Savage to work, since you'd still have to figure out the barrel extension locking lug half of the equation. Heck, if that bolt handle is removable, you could attach your cam pin right there :cool:

No good pictures of the bolt face, for some reason, but you get the idea;

"i tested the shear of the locking lugs.. but not the entire locking lugs.. but the tip along the line that contacts with the locking surfaces within the barrel.."
For very small locking lugs like the AR's which have a high aspect ratio (length to cross section area) failure modes like bending and shear are more critical, and contact failure by peening is less critical (since there is so much more effective area to load up). When you go to a smaller number of larger lugs, the opposite occurs, and bending/shear stop being the driving factor. At the very least, as a sanity check, compare the contacting surface area of your bolt head to that for other 308-class rifles with similar-size bolt heads (a Remington 700's bolt area would be good to compare with, for example, or maybe a FAL's. An AR10 might be a useful data point, but the lugs are so different that other factors may come into play, namely that the bolts aren't contact-load critical. An FAL for sure is, since both sides of the lug are massive blocks of metal abutted)

"so a lot of thought has to go into finding a good muzzle brake thatll reduce even more recoil but still be comfortable enough to shoot without ear protection"
Do a Form 1 and make it integrally suppressed (heck, make the suppressor part of the action --an insanely large volume muzzle booster :cool:)

I would suggest you use round tubing if at all possible. 4130 DOM round tubing is available in a vast array of sizes and thickness, and has very good internal/external dimensions and smoothness. No boring/turning would likely be necessary. Square tube, like I'm using for my Skorparev design, is extremely limited by comparison, and is very expensive (~40$/ft) to get in small quantitites. I was only able to find one supplier who'd answer my calls that sold the 7/8" tubing that will telescope in my 1"x.063" wall receiver tube as the bolt carrier/piston. Also, it's apparent that some amount of warpage variance occurs in these tubes, so tight fits are a very bad idea (which is why I have a round piston head/gas tube inside the square receiver tube).


May 2, 2014, 07:16 PM
ive thought about having the cam groove on the small half inch shank of the bolt head so the cam surface was between the bolt head and the bolt body.. but instead the way i have it now is that the bolt head fits inside a piece of 5/8" steel tube, the cam groove will likely be cut in this groove (imagine an FG42 or a K31 bolt.. which as it stands my straight-pull bolt action using this same bolt will most likely end up being pretty similar to the K31 bolt action rifle but with something more like the savage 10 barrels or the similar remington 700 barrels i believe i seen made by bergara

but enough about that.. about the design i have now, ive lowered the ejection port a great deal, it now ejects at a 22.50" angle which allows the cartridges to eject underneath the rails so the top of the ejection port is right under my top rail.. also, the carrier isnt so bulbous and top heavy looking, ive moved the majority of the weight more towards the center, much closer to the bore of the rifle and saved a total of .1lb

its likely this wont even be the final bolt carrier because if im going with something more like the FG42/K31 bolt, then i may use a similar style bolt carrier but at this point i fear that may make the bolt carrier TOO light weight.. too low of a bolt carrier mass and reliability will go down (AKs are reliable not because of their piston design but because of the higher mass carrier)


the gas system i wanted before which would have used an oprod on the carrier that was bored out in the top to act as a gas key for an AR-15 gas block and tube, cut to length apparently will not work.. the shorted i could make the oprod without it popping out of the trunnion with the carrier fully rearward is about 6 inches.. minimum barrel length i could have is MAYBE 8 inches which is plenty short enough anyway but kind of renders my entire gas system idea useless

furthermore, i wanted to reduce the weight of my bolt carrier to around 1lb as it would still be plenty reliable with enough mass but reduce some of the extra weight.. so what im thinking of doing right now is removing the oprod entirely and going with a short-stroke system.. the way ive considered setting up this short stroke system was to build the piston into the front trunnion by adding a tubular extension in front of it for the piston to sit in.. it would have .25-.5" of travel before gasses are vented in front of the trunnion and then i could use the AR-15 gas block and gas tube to bring gasses rearward to the trunnion mounted short stroke piston.. benefit of this is i can use any AR-15 gas block (since my barrel is set up for a .750" gas block anyway), and it allows me to bring the center of gravity of the rifle more rearward.. though im still not opposed to using something more like an FAL gas system on this rifle

current weight 7.5lbs

heres what my gas system would have looked like as originally intended

May 2, 2014, 08:03 PM
"AKs are reliable not because of their piston design but because of the higher mass carrier"
That makes them a bit more reliable at stripping rounds off the mag and not getting stuck, at least (but obviously mag design is even more critical to function/reliability). It also makes recoil harsher as the gun cycles, though :(. That's why belt feds are (all?) long-stroke actions with big, heavy pistons and carriers that can smash a round through/from those links without stopping. On that note, one gas-system idea you may want to visit is making the gas tube short enough that the piston head actually exits before a full stroke; the actual driving portion of the piston throw is of course shorter than what's needed to unlock the bolt, and if your carrier-on-rails has a rigid piston extending off it, all you need is a chamfered gas tube opening to guide it back in (and a shroud to keep hands away :eek:). This is how the big bruisers work, or at least the ZB37 and UK59 that I'm acquainted with (both have BREN-like carriers and gas systems) bolt carrier is at the top, there; the piston is only like 2" long BREN has a more 'conventional' piston length, but it is fully out of the gas tube and inside a guide tube within the first 1" or so of its travel, if memory serves

A K31-like bolt sleeve is a really cool idea; you could conceivably have an aluminum bolt carrier since no sliding contact of significance will take place against the carrier (rather the sleeve and bolt). Very high potential for weight and recoil savings, there.


May 2, 2014, 11:26 PM
well there are a few factors that make the AK more reliable than other rifles.. magazine design, the fact the magazine is curved, the fact it mounts to the same platform as the barrel (magazines mounted to a lower receiver can feed rounds at off angles if the lower isnt properly fitted), no carrier jumping from the upper to the lower like on an AR-15.. again, if the upper and lower arent fitted properly this will cause problems, but the thing that contributes the least to its reliability is its gas system.. in fact, its little different than any other short stroke system.. and my comment about the carrier weight allowing for better reliabiltiy was aimed more at the fact that the extra mass carrying extra momentum is better able to overcome obstructions, debris and friction than a low-mass carrier

you know, i really do like that gas system design i sketched out above.. i just dont think its all that practical, i mean.. you can easily adjust the stroke-length (length of time the piston is under the impulse of the expanding gasses) of the gas system simply by drilling the pocket in the oprod deeper or shallower.. as the oprod pulls away itll separate the oprod from the gas tube and vent the gasses

now im starting to think my idea with the shortened short-stroke piston which is mounted to an extension of the trunnion may not be the best idea for this application.. im considering using an interrupted thread with a detent or a lever for removing and installing the barrels.. it would be very difficult to push a barrel on and twist it and expect the gas tube to fit inside the cavity where the gas piston is at

so im thinking i may have to go with something like the FAL, or M14 gas system, or still go with the idea i originally had since the barrel is installed while the bolt carrier is removed or at least locked back.. i dont know, i see the merits of being able to use widely available ready mad gas blocks but i dunno.. this seems to be the biggest block i have right now in determining what i need to do moving forward


question though.. if i used two guide rods that went through the entire bolt carrier and fit into the back of the front trunnion.. would these be sifficient enough to be used as rails?

May 3, 2014, 03:49 AM
heres a concept of the one gas system i tried to describe earlier.. its a short-stroke piston built into the trunnion.. theres a block in the back side of it that holds the return spring, and a cap that threads over the end of that really short gas tube that sticks out the front to hold the piston in.. and you use an AR-15 gas block and gas tube to bring the gasses back from the gas block and to this piston.. so this is a photo of my front trunnion which i have made translucent so you can see the piston.. foreseeable downside to this is it would bring a lot of heat into the trunnion.. a lot more heat in the receiver.. may not be the best idea

May 3, 2014, 09:23 AM
I think the bigger issue would be you'd be tapping gas right at the neck of the cartridge, potentially. For rounds like 308, it'd likely still be on fire, and not the most gentle substance for your piston/spring parts to be playing with. I think the real issue with heat in the trunnion would be de-tempering of your piston spring (probably not an issue on a semi-auto used responsibly, but it has similar drawbacks to barrel-centric springs on olde-tyme machine guns like the DP28)

What if you eliminated the spring entirely, and just used a loose tappet? If the burning gas is not an issue (who knows, with stainless steels it may not be) a loose tappet would never have a spring to de-temper, and would be light enough that the returning carrier could push it back forward without losing much momentum. The piston would be fully forward in battery, so no annoying rattle when moving the rifle.

For lower-gas volume rounds like pistol rounds, a captive piston in the trunnion would be a great way to shrink everything down and keep it modular.

There's no reason two guide rods out of the front trunnion wouldn't support the carrier sufficiently, provided they are thick enough. As you know, lots of designs use dual rods to guide bolts/carriers. If you're suggesting they would only be supported at the front trunnion, that'd probably still work since the carrier is under greatest load at that end, where it has the most support. You'd likely need to beef up the rods and trunnion seat a bit to keep everything rigid, though.

One other thing that might be a good idea is to make your return spring for the bolt in line with the piston. You are already impacting the bolt offset from its center of mass, trying to spin it against the rails, so the last thing you want is extra off-axis force from a low-set recoil spring. The VZ58 is a great example of what I'm talking about (the bolt carrier has a deep hole drilled for the return spring to collapse into, and the far side of the hole is the face that is struck by the short stroke piston). Keeping the return spring raise up makes it easier for FCG parts to reach the firing pin part of the bolt, too (which is why the VZ has room for a striker)


May 3, 2014, 10:47 AM
for the gas system i showed you, gasses wouldnt be tapped off the barrel in this location but from a normal AR-15 type gas block further down the barrel, out of this gas block would be the gas tube which would bring gasses from in front of the rifle to the gas piston.. but would it be a good idea to have the hot gasses this far rearward?.. i mean, the AR-15 sends gasses even further back so its still much better than that system, and would maintain a similar balance to the rifle by having the weight more rearward

and as it stands now i have the area behind the oprod (or area where the piston strikes if i go that route) bored out for the recoil spring and a telescoping guide rod

what i was thinking of doing was removing the rails, and drilling two holes completely through the bolt carrier behind where the rails would have been and run two guide rods through the bolt carrer and into the back side of the trunnion.. when closed the rod would be supported in the front by the rear of the trunnion, and in the back by a removable block that will hold the recoil spring too.. for field stripping you just break the action open, grab that block and pull everything out, itll likely all be captive with the carrier

does the AR-18/AR-180 use rails in this manner or do they have something attaches to the receiver that the bolt carrier rides on?

May 3, 2014, 11:23 AM
The AR180 is like the AR70; receiver's just a square tube the carrier rides in, and the bolt uses the floor as keying rails. The square tube attaches to a forward trunnion block, not unlike a G3 in construction, but square.


May 3, 2014, 11:51 AM
i guess if i had the oprod stay in the trunnion, i would only need to have an extended surface contact the inside walls of the receiver to keep it centered.. so i guess with the longer oprod i wouldnt even need rails, or guide rods since between the oprod and two sides of the carrier the bolt wouldnt have any movement in any direction besides forward and back

would you agree that the walls of this trunnion look way too thin?.. especially if it were to be threaded with interrupted threads or threaded savage style barrels?.. im thinking of making my receiver thicker so to be able to have more meat in this area.. which means i either have to step up to a 1.5" piece of square tube steel with half a piece of .75" tube steel for the dust cover, or go with a 1.5x2" piece of rectangular tube steel.. or the third option.. designing a simple shape that best fits the design that can be made of sheet metal bent on a shop press and welded at the seams.. maybe dimpled on the sides to stabilize a thinner bolt carrier

May 3, 2014, 02:14 PM
Though it looks like you've moved away from the recoil-operated concept... last year I bought a Remington Model 8, a long-recoil rifle designed by John Browning. The bolt and trunnion setup look amazingly like an AK-47, except the whole assembly recoils when the rifle is fired. A big spring wrapped around the barrel, with a sheet metal shield, moves it all back into battery. (8 aficionados call it the "pogo stick").

Shortly after buying the Model 8 I picked up a PPS43 kit. While they were both on the bench, I noted that much of the exotic machine work of the Model 8 could be replaced with stamped sheet metal like that of the PPS43. You'd only need to machine the trunnion, bolt, carrier, and a few bits; the rest could be cut and bent from sheet like the AK and PPS kit builders do.

The recoiling barrel of the Model 8 gets a lot of bad publicity, but it was accurate enough to stay in production for decades. Though with a PPS-style barrel shround, you could update the design with a 1911-style barrel bushing...

The trunnion and bolt parts of the Model 8 aren't complex, and there's a lot more metal in a Model 8 trunnion than an AK trunnion, even though some AKs were made in .308 and other medium calibers. Most of the rest could be low-tech sheet metal.

May 3, 2014, 02:38 PM
Though it looks like you've moved away from the recoil-operated concept... last year I bought a Remington Model 8, a long-recoil rifle designed by John Browning. The bolt and trunnion setup look amazingly like an AK-47, except the whole assembly recoils when the rifle is fired. A big spring wrapped around the barrel, with a sheet metal shield, moves it all back into battery. (8 aficionados call it the "pogo stick").

Shortly after buying the Model 8 I picked up a PPS43 kit. While they were both on the bench, I noted that much of the exotic machine work of the Model 8 could be replaced with stamped sheet metal like that of the PPS43. You'd only need to machine the trunnion, bolt, carrier, and a few bits; the rest could be cut and bent from sheet like the AK and PPS kit builders do.

The recoiling barrel of the Model 8 gets a lot of bad publicity, but it was accurate enough to stay in production for decades. Though with a PPS-style barrel shround, you could update the design with a 1911-style barrel bushing...

The trunnion and bolt parts of the Model 8 aren't complex, and there's a lot more metal in a Model 8 trunnion than an AK trunnion, even though some AKs were made in .308 and other medium calibers. Most of the rest could be low-tech sheet metal.
i havent moved away from recoil operation, thats a separate design im working on.. ill try to describe how this setup works for the short recoil im working on

when you close a rotating bolt, you need the carrier to rotate the bolt because the bolt face has to be against the breech of the barrel before it can begin rotating.. if you were to try to rotate the bolt by having the bolt ride inside a cammed groove inside the receiver of a typical rifle, it would be impossible to lock it on a flat surface, having a delayed blowback at best.. this of course is all talking about a typical gas operated rifle

for my blowback idea.. i intended on having the groove the charging handle rides in by angled at the end of travel, so the charging handle groove will rotate the bolt as well.. now my solution to make this work so everything locks on a flat surface is to have the bolt face and breech of the barrel contact eachother.. and then both the bolt and barrel travel together for another half inch while the bolt is turning to lock into the barrel

because the bolt and barrel travel together for a short distance youre able to turn the bolt directly without a bolt carrier and lock it on the flat surface of the locking surfaces inside the barrel.. if the two didnt travel together a short distance as stated above, this would be impossible

so the solution i worked out was that the barrel would fly back for about half an inch and stop.. some mechanism would hold the barrel rearward while the bolt cycles.. this mechanism could be as simple as a spring holding it all back.. after the bolt travels rearward and comes back to the front, the bolt face and barrel breech meet at which point the main spring overpowers the spring holding the barrel back and the two assemblies are able to travel forward together while the charging handle is turned as it travels within the groove cut for the charging handle.. this will turn the bolt, locking it into the barrel just before the two assemblies rest fully forward


benefit of this system is that theres no need for a bolt carrier, no need for any kind of internal machining of the receiver, and the final product is a fully locked short recoil operated rifle capable of firing any caliber you decide to design it for and the entire setup is barely more complex than your common blowback submachine guns like the sten, grease gun, sterling, etc

May 3, 2014, 02:44 PM
That trunny does look a little thin. So you are planning on a threaded-type barrel attachment (as opposed to a pressed/pinned affair)? One thing you might consider would be making the threads external, and using a threaded collar to pull the barrel journal into the action (like an AR or Savage rifle, IIRC). That way, the expensive part --the trunnion-- can be a little smaller, and the cheap non-load-bearing collar can be made from Aluminum or low-grade steel.


May 3, 2014, 03:44 PM
theres a couple ways im considering the barrel/trunnion setup.. one was to use a steel trunnion, locking lug surfaces machined into the trunnion using savage 10 barrels which are threaded on by hand, and then the collar is tightened down over top

another way i was considering it is having a barrel possibly pressed and pinned into a barrel extension, of the locking lugs could be machined directly into the barrel itself.. this could be attached with interrupted threads and a detent to lock it in place.. kind of like a steyr AUG barrel.. then the trunnion could be made out of lighter aluminum

the third option again is with the lugs in the barrel or barrel extension, attached in some other manner.. not sure if a lever would be enough where youd push a barrel in then turn a lever which would have a semi-circular shaft that would lock the barrel in like a pin.. or screw the barrel in from the sides like on the FN SCAR which uses four screws to hold the barrel in.. problem i have with AR-15 barrel nuts is the barrel nut is very large, takes up a ton of space and forces the gas system to be raised high enough to get around it

so... what im leaning on is either a steel trunnion with a savage barrel mounted to the trunnion, locking lugs in the trunnion, or using an aluminum trunnion with the barrel or barrel extension mounting inside the trunnion via the interrupted thread for an even quicker, simpler barrel change

with the removable bolt head, interchangeable magwells, having an easy, simple way to change barrels would allow this rifle to function well as a multi-caliber rifle


the other way im loking at the rifle is this.. if my upper receiver is just a piece of tube steel it would be very easy to have barrel fixed to its own upper receiver.. magwell could likely just be riveted or welded on to match the caliber of the barrel installed and just swap out the BCG and lower receiver to change calibers

you know what i could do?.. i could make an extension of the trunnion like you see on the front of the AR-15. but design my own collar to go over top of it.. likely using an interrupted thread.. downside is youd still need a separate barrel nut for each barrel.. but it does look like im going to need to make my trunnion a bit larger leaving me with three choices.. square tube steel with a dust cover, but using 1.5" tube steel, i could use 1.5x2 inch rectangular tube steel.. or design a folded sheet metal upper thats simple enough to fold with a shop press and some basic dies

by the way.. the inside diameter of that trunnion where the barrel fits into is 1" in diameter

May 3, 2014, 08:54 PM
anyway, to try to better organize what im trying to say here is that there are two areas that im currently stuck on and not 100% certain which decisions to make here.. the gas system, and the barrel attachment mechanism


of the gas system my choices are these

1. FAL style short stroke piston
2. M-14 style system with an oprod and piston built into the gas block
3. AR-15 gas block with a "key" machined into the front surface of the oprod for the gas tube
4. short stroke piston built into the trunnion, an AR-15 gas block and gas tube will bring gas from a forward location and divert it rearward to the piston.. adjustable AR-15 blocks can be used

options 1 and 4 will require me to NOT have an oprod on my carrier and therefor some kind of internal rails must be used.. possibly two large guide rods mounted between the rear of the trunnion and the block retaining the recoil spring in the back of the carrier


my options for barrel attachments are

1. thread the trunnion, use savage 10 barrels and barrel nut, requires headspacing between changes, locking lugs in the trunnion
2. locking lugs in the barrel, either threaded on by hand until a detent locks the barrel in place or an interrupted thread is used to do the same thing but easier and in less time
3. trunnion extends forward with the threads on the trunnion, uses a threaded barrel nut or interrupted thread barrel nut and a detent to lock the barrel in place
or 4, im not even sure if this is secure enough, or would hold zero well but the barrel is pushed into the trunnion by hand, not pressed, and a hole is drilled along the edge of the barrel to drive a pin through, or a semicircular shaft mounted on a lever

another idea i have is to machine a few lugs inside the front of the trunnion of the rifle, then machine some grooves onto the bode of the barrel so the barrel could be placed into the trunnion, and given a little twist to lock in place

May 3, 2014, 10:51 PM
Of your options:

1) Short stroke is most useful on open top receiver guns (VZ58, SKS, FAL) since there is no piston rod in the way as the action opens. If your design has no need for such, the only real benefit to this system is ostensibly less felt recoil

2) My main beef with the Garand/M14 system is how complex and convoluted the line of action from piston to bolt is. It's always astounded me it works as well as it does since that curvy rod has to be flexing and bowing like crazy when loaded up by gas pressure. Believe it or not, an mere AK47 is functionally very close to this system in operation, but putting the gas tube up top allows everything to be straight (and the beefy bolt carrier is just to hold the bolt instead of a complex receiver forging)

3) If an AR15 bolt will not function with a clogged/blocked gas key since the small tube won't push on the carrier hard enough across such a small area, can your piston be sized large enough to operate and remain compact? Also, you'd obviously have to do a better job than Stoner did making sure your bolt carrier can't tilt from the off-axis thrust, but that's an issue intrinsic to all piston actions. My main point about the gas tube is that a long skinny tube is incredibly inefficient in telegraphing pressure and mass (gas volume) which you'd need for a piston operation. You might as well use a full-on gas tube (and if made for a very common tubing size, any cost/availability gains from using the AR tube would be more than regained)

4) Same possible issues as number three. Instead of blasting a little tube's gas at the piston face, which is sure to be a lossy and leaky affair, you might just use a 'remote gas block' at the front of the trunnion to retain the piston, align/secure the tube, and seal the gas delivery until the piston uncovers vent holes. I'm not sure how much you end up saving over a longer piston or normal-style gas tube by using the AR tubing. A hollow pipe piston rod would weigh exactly as much as a hollow pipe gas tube, and infinitesimally more than a slightly-smaller diameter AR gas tube that's more complicated due to bends and swaging.

For barrel attachments:

1) I'd avoid this; it's been done a zillion times and isn't very interesting from a design standpoint :D. Barrel extensions are really the wave of the future; there's precious few advantages to putting the lugs on a larger separate trunnion
2) This is an easier to make solution. Do look into the BREN barrel attachment method; very clever way to do fast-change barrels (it's an interrupted thread collar attached to the carry handle for leverage)
3) This will allow a smaller trunnion diameter than number 2, but will probably end up being a larger package when you count the collar diameter. If the collar is no fatter than the rest of the rifle, there's very little reason to go with an internally threaded trunnion over this
4) For a barrel with integral lugs in an extension, this would probably work, at least depending on what levels of recoil you end up with (the barrel thickness at the chamber and pin diameter would need to be sized for max recoil, of course). I think this is sort of how the ARX160 works, but they have a vertically sliding block that secures the barrel/extension (not unlike the takedown levers on Beretta pistols)

Your last idea is very similar to how the Suomi attaches its barrel shroud (long story; the Suomi shroud is attached as firmly as any barrel, and itself acts as a collar to hold the barrel into the trunnion. It's a big reason the guns are so accurate). The nose of the receiver is four large square lugs, which align with mating lugs in the shroud. A simple locking lever swings up and blocks the shroud from rotating backward and coming loose. While it works great, the drawback is that the force required for every moving part is extremely high, since you don't have the mechanical advantage of threads helping clamp everything together. Part of it is machining tolerance making some shrouds much tighter, but even the loose one' require strong hands to put together.


May 3, 2014, 11:23 PM
well... i think im going to go with an oprod anyway.. the extension of my bolt carrer you see sticking out the front.. i dont think i will use a gas tube to bring gasses back, theres really not much added weight to be saved here to make it worth it.. so from this oprod i will either have a piston mounted on the end of it that will go inside the gas tube, or i will have a small short-stroke piston head inside the gas tube

now.. what would the advantages to having the piston head separate be over attached to the bolt carrier?.. does seem like there would actually be much of a different in function here.. does a short gas piston provide any benefit thats worth the added complexity and higher parts count?

since im going to go with the op rod, its going to provide a certain level of stability to the bolt carrier.. and make carrier tilt very unlikely.. and it also means i dont really need any rails either.. the oprod prevents the carrier from tilting forward or back, or side to side and the edges of the carrier itself will prevent it from rotating

also.. i intend to put the recoil spring on a telescoping guide rod, the entire spring will take up most of the interior volume of the hollow oprod, like on the AK which should allow the BCG to get closer to the back of the receiver and allows me to shorten up the rifle


so.. either i will go with something like that BREN used, piston head attached to the oprod attached to the carrier goes inside the short gas tube.. gun fires, carrier recoils back and the piston exits the gas tube and the gas vents.. i could bell the mouth of the short gas tube to make it easier for the piston to re-enter the gas tube after it comes back

or the other option, installing a short little piston in the gas tube like on a SCAR


now i just need to figure out what i will do for attaching the barrel and im considering doing what the steyr AUG and also i believe what the suomi M31 does.. or going with a simple interrupted thread with a lever or a detent to hold it in place but first, at least for my prototype to keep it simple i will have my locking lugs in a steel trunnion set up for savage 10 barrels.. sure ill need to headspace whenever i change a barrel, but thats not a problem


one more question though.. the lower part of the trunnion where the barrel is mounted.. do you think it would be possible to press a threaded bushing into an aluminum trunnion?.. the bushing would be wider on the breech end, barrel threads into it from the muzzle side of the trunnion and it locks down with a barrel nut?

May 4, 2014, 08:41 AM
do you think it would be possible to press a threaded bushing into an aluminum trunnion?

It's possible, but there are some things that come to mind as a result:

- Galvanic corrosion between the bushing and trunnion. More of a long-term issue, but appropriate protection would be required.
- Stress corrosion of the trunnion. Could result in catastrophic failure after some time due to static stresses resulting from the press fit. Many aluminum alloys are susceptible, and this has been a documented mode of failure in service. Proper aluminum alloy and heat treat condition selection would be required.
- Balance the amount of interference such that endurance limit at a particular life isn't exceeded with the addition of tensile stresses at the hole due to the press fit.

May 4, 2014, 11:20 AM
"what would the advantages to having the piston head separate be over attached to the bolt carrier?"

Nearly every short stroke* design I've heard of (VZ58, SKS, FAL, Simonov, L-39 I think) has an open-top receiver layout, where the bolt carrier closes out the entire top half of the action when in battery riding on frame rails at its base. The other (true) direct-impingement designs, the Rasheed and AG42/hakim, also have open-top receivers since there is no fixed piston in the way. Why the AR doesn't as well is yet another mystery of the most odd of historical gun designs.

The SCAR and Browning BAR hunting rifle are a different sub-variant of the short stroke family in that the pistons are extremely small, 'tappet pistons,' and really serve to dampen and delay the gas impulse delivered to a 'long stroke style' bolt carrier with a long forward protrusion reaching to the tappet, for the purpose of making the gas operation a little less dependent upon the ammo's pressure curve (whatever it is, it is compressed into a single impact of the piston on the op-rod/carrier extension). However, the bolt carrier still has a large forward-reaching body on it, so the open-top receiver layout is not possible, and side-ejection is used instead, just like a long-stroke deisgn.

The extremely short stroke of the tappet piston has the benefit of keeping gas debris further forward (my FNAR requires piston cleaning every 1000rounds or so, as does the SCAR IIRC). 'Full size' piston short stroke systems have the effect of damping recoil, since the piston and bolt/carrier do not hit their full rearward travel at the same time (and if tuned, the carrier bottoms out on the receiver the same instant the piston returns forward)


*I personally define 'short stroke gas operation' as a piston which strokes less than the bolt/carrier. By definition it must separate from the bolt carrier, so to me it is shorthand for a piston that is separate from the bolt carrier. 'Long stroke gas operation' is for a piston that is effectively rigidly attached to the carrier through the whole cycle.

May 4, 2014, 12:06 PM
thats what i was curious about.. the tappet piston vs just an attached piston to the carrier like on the AK or garand.. seems to me the tappet piston may be better for a variety of calibers which may be one of the reasons the FN SCAR went with that system

so its either that or something more like that BREN system.. i can have a 6 inch extension to my bolt carrier, and add a 2.5" AK pistol gas piston to the front of that if i wanted to go that route and have an adjustable gas block


right now im just trying to determine how important it is to stay as light as possible.. if i go with an aluminum trunnion, then i need some other form of interior rails because i wouldnt want the carrier extension riding so closely on top of aluminum.. id likely use some kind of a bushing that wouldnt re-act with the aluminum but still offer more protection but put all the work and not the weight on the interior rails instead of which would either be the rails i have now or the guide rods

so theres some decisions i need to make now that will have its own tradeoffs, mostly, i just need to sketch out each idea into inventor and see which one i like the best

May 4, 2014, 12:53 PM
Be warned; the BREN system is basically a belt fed, so it's really heavy for its size. That giant op rod with a bolt carrier and bolt stacked on it are truly massive. It's cool that the receiver of the BREN is basically just mild-steel box tubing, but at what cost?

I will say the BREN system is more adaptable to different barrel lengths, since you'd just screw in a different length/diameter piston on the op rod.


Just to make sure I understand your terminology;
Piston: cylindrical lathe-turned element of the system absorbing and transmitting gas pressure force/momentum
Op Rod: body integral to the bolt carrier assembly which receives the piston impulse either by contact or by rigid attachment
Bolt carrier: body integral to the bolt carrier assembly which actuates the locking action of the bolt body
Bolt body: lug-bearing element which carriers the actual bolt thrust of the chamber pressure and mechanically latches to the receiver or barrel extension

I personally tend to use 'bolt carrier' for a mass larger than the bolt which actuates it and receives piston force; 'piston' for the element(s) solely there for the purposes of delivering gas force to the bolt carrier, and 'op rod' for those rare designs like the Garand wherein the bolt carrier is smaller or non-existent as well as integral to the piston in a single 'rod-like' part. I think your definitions make more mechanical sense, though (mine are sort of just based on what stuff looks like :D)

May 4, 2014, 01:54 PM
when i meant bren system i just meant the way the gas system appears to function, mine wouldnt be anywhere near the weight though.. im leaning towards either that or the tappet.. if i go with an aluminum trunnion id have to add something else for rails to take the weight of the trunnion and it would appear actual weight savings may not be all that great in the end.. so thats why im leaning towards a steel trunnion with the extended portion of the carrier at this point

im going to design the rifle to use the two oprods with an aluminum receiver and some type of gas system that isnt going to cause a lot of steel on aluminum friction and see how much weight savings, if any, there actually are.. kind of makes you wonder how the piston conversions on the AR-15 would wear on the aluminum hole the gas tube used to go through which is not a moving component?

May 4, 2014, 02:24 PM
You mean they don't use a bushing? That is stupid. Now I understand the issues many folks report with those. That and the fact there is pitifully poor directional support for the bolt carrier as it retracts, which is even more critical when you apply force at the top like that.


May 4, 2014, 03:09 PM
i dont know if the AR-15 uses a bushing or not, none of the kits ive seen used them, and the idea you have the steel carrier riding inside the aluminum receiver is a pretty dumb idea to me too, id like to avoid steel on aluminum friction because that almost always means excessive wear of the aluminum part

in fact, ive been thinking of the two ways i have to mount the trunnion into the receiver, weld or rivet and i was leaning towards rivet because it would be much easier for a builder trying to build this rifle to buy a pre-made trunnion and rivet it in than it would be to weld it in and then have to heat treat everything afterwards, though the weld would be much cleaner.. in either case it seems steel would be the better material here so i think im moving ahead with a steel trunnion and the extended portion of the bolt carrier

so what do you think?.. short AK pistol piston at the end of the extended portion of the carrier, or the tappet piston similar to what a scar and i believe the M14 has?.. as for the extended portion of the carrier thatll be basically a pipe welded into it.. it doesnt really need to come out for any reason

May 4, 2014, 04:54 PM
Welding does not equal heat treating; neither my AR70 nor STGW57 required heat treating of the receiver after weld up; just use a TIG and keep the heat local. For people with welders, that's far easier than rivets, and vice versa for people with rivet squeezers. Personally, I think if you can do a rivet design, you could do a screw-together design just as easily. A friend of mine did a screw-together PKM (giant belt fed AK) with Allen caps crews into the tapped trunnion holes and it came out looking very good.

I would go with a fixed piston on the carrier for simplicity, at least for version 1.0. I would also endeavor to have my guide rails in line with the piston/op rod so there is less binding working against you (the BREN and others had the rails along the sides of the carrier/piston/op rod, rather than the bolt, which just floated on top of it). Does the M14 have a separate piston? I thought it was similar to a shortened Garand's, but of course totally incompatible.


May 4, 2014, 05:13 PM
yeah, M14 has a short gas piston, its a bit different gas system than the garands and if im not mistaken it was also a lot more reliable

also i was thinking of doing a screw build for version 1, just to make it easier to remove the trunnion and put in another one if i needed something changed

as it stands now, this is my carrier with the intention of ejecting at about a 22.5 degree angle which places it right at the center of the flat side of the carrier on the section beneath the rails.. so the rails are above the ejection port and you can also see the rails are much closer to the extended portion of the carrier.. there is a hole going completely through the bolt carrier and through the extension which is hollowed out, my intention has always been to place the recoil spring here, behind the piston inside the carrier extension, even if i added two "guide rods" for the carrier to ride upon like rails i still intended to leave the spring behind the piston

as these flat sides are against the inside walls of the receiver, the carrier could not rotate side to side.. that combined with the protruding extension to the carrier inside the front trunnion means there really wouldnt even be a need for those rails.. im wondering though if it would be better to have the majority of the carrier mass higher up around the rails and piston, or more centralized like it is now

May 4, 2014, 05:28 PM
"yeah, M14 has a short gas piston, its a bit different gas system than the garands and if im not mistaken it was also a lot more reliable"
Neat. I'd never really looked at it in depth before; it's quite similar to my FNAR in terms of function (only an expensive Garand op rod rather than stamped sheet metal rails being struck by the piston). The self-regulating aspect of short stroke tappets is one of the key selling points on reliability. Like all things, I'm sure it only compensates over a certain range of input pressures, but it does appear to give the same system the ability to ingest a wider variety of ammo (I also suspect they require a lot more complex design and development work up front to get running than a solid piston setup, though, which is why I suspect they have not been as popular until recently starting with the G36, SCAR, ARX160, MP7, etc.)


May 4, 2014, 06:34 PM
does the g36 use the sort of tappet piston as well?

May 4, 2014, 07:23 PM
The G36 is arguably the first of the current crop of 'next gen' rifles that all share;

-Short stroke, self regulating gas piston (tappet style)
-Radial lug AR-style bolt head and barrel extension with lugs
-Reinforced polymer tube construction for upper (a few are clamshell, though)
-Fancy coatings that supposedly negate the need for cleaning/lubrication (where have we heard that, before?)
-Fast swappable barrels
-Lotz 'o railz and other allegedly-modular features

Pretty much every 'hot new' platform has shared at least a couple of these features; G36, SCAR, Tavor (long stroke), MP7 PDW, MPX, ARX, BREN 805, HK416, and I think a couple of the various super-rifles that never made it out of R&D. The H&K G3, AK47, and M3 grease gun were products of automotive manufacture; the AR15 the product of aerospace manufacture technologies (even to this day, with its newfound reliance upon CNC); the new generation rifles are, I guess, products of iPhone manufacturing technologies :neener: (or perhaps Keurig coffee maker technology :D)

Extremely interesting and technical article on the CZ805 BREN's development, operation, and introduction;
Monolithic aluminum square tube upper with a G36-like bolt/carrier and gas system much improved over the SCAR. Supposedly they're working on getting them over to us, but they did only win the Czech military contract in '09 so I assume they are still a bit booked up with government orders for a good while. One day...


May 4, 2014, 10:18 PM
oh i already know about the CZ-805, only "next-gen" rifle id actually spend money on.. i mean, atleast until i recently decided to design everything i get from now on.. be it a military style semi auto, a bolt action, handguns, whatever.. anything else i buy from here on out is just going to be the more less common designs if i can get them.. heck ive even thought about taking the luger toggle lock action and improving upon it for use in a rifle.. since the luger rifles are so rare and werent really even made, it would be nice to have something based on that that would function.. but thatll be a later project

you know.. i have to admit i do really like the open top designs like the garand, M14, G43, SVT, FN49, SKS, etc, so im not entirely opposed to doing that with the rifle im working on now.. i mean, the top of my receiver is a dust cover i could actually shorten and the lower and magwell could easily bolt on from below, sandwiching a full wooden stock in between.. so dont tempt me too much or i may just end up doing that... i also like bullpups too, i think theyre great for close quarters stuff like home defense and i love the balance

honestly.. thats the only fear i have with this rifle im working on.. having it end up too much like everything else out there.. there doesnt really seem to be one thing about it that stands out.. if i follow the mould too closely you begin with think "whats the point?"

May 4, 2014, 10:46 PM
'fraid I can't give you too much advice, except so say that an open-top bullpup probably won't fly :p

"having it end up too much like everything else out there.. there doesnt really seem to be one thing about it that stands out.. if i follow the mould too closely you begin with think "whats the point?""
I think all you can do is try to define a role/purpose for your platform that isn't quite fulfilled by whatever else is out there, and doggedly pursue perfection along that direction without regard to what people are used to. For me, it was light carbine that's not quite as big/powerful as an AR, but got more going for it than a blowback pistol caliber SMG; the compactness and light weight of a 'tactical pistol' as well as their high capacity, and near-rifle ballistics. For such a light/handy rifle, I figured intuitive ergonomics would be even more paramount than they are for rifles, since the carbine's role would overlap with pistols who's ergonomics are very developed in comparison to rifles (which pretty much mirror the manual of arms of rifles dating to the Victorian age, with manual safeties, single action triggers, and selector levers)

If you are hoping to single-handedly create a better version of an existing rifle concept, let alone a very common and competitively pursued concept like a battle rifle, it is extremely unlikely you can develop something that can compete out of the gate with designs that have been perfected for decades. I sure wouldn't try to design a 'new' type of tilting barrel pistol to go up against Glock and CZ, for instance. A single stack 5.7x28 'mouse gun that roars,' however, would likely have little competition for a good long time ;)


May 4, 2014, 11:24 PM
well, id have to say a key feature of this design is just how low cost it is to make.. im looking at a rifle that could be sold retail for $600-$800.. with the same weight, features, and recoil characteristics of a $3000 SCAR with the ability to change calibers.. so the ability to provide the same features at a mere fraction of the cost with the ability to easily build yourself would be the goal

you know, i could provide all these features.. throw out the AR-15 stock, pistol grip, aluminum forearm and fit everything into a wooden or polymer stock like an M14/M1A or an FN49.. doesnt necessarily have to be open-top either.. i could put the bolt up on top of the carrier and make it side eject with the ability to place a rail across the top of the receiver and still have simple barrel changes, and mutli-caliber capabilities.. something not present in any full-stock rifle


you talked about making a pistol that had more power than a handgun, though not as much of a rifle.. i was actually thinking of similar ideas.. i noticed that 357 magnum fired from a lever action has MORE kinetic energy than a .223.. so it had me thinking if it was possible to design an auto cartridge capable of higher energy levels, could be chambered in a handgun with a magazine small enough to fit in the grip, and used a spitzer bullet for better range... so below is a photo of a cartridge i sketched out.. its based on a .308 winchester case necked to 6.5mm and shortened to an overall length of about 40-41mm, same length as the 44 mag and 50AE you can chamber in a desert eagle.. what do you think?.. this would be a different project of mine if i went forward with something like this

same base diameter as a .45acp means i could fit about 14 of these in a double stack magazine.. this has roughly the same case capacity as a .222 remington, i may move the shoulder back and shoot for a similar case capacity of a .300 AAC blackout

May 5, 2014, 07:43 PM
well i was talking with some other people i knew that was discussing gun design with me, and well, we all came to an agreement.. we're sick and tired of tacticool everywhere.. i like old school, i like rifles like the M14, SVT, FN49.. so using the same rifle for the most part, im going to tweak this into a full-stock rifle with all the same features of being able to easily change calibers.. but my stock will resemble something more along the lines of the FN49 stock with side eject and the capability of taking a top rail for sights and optics

heck, even the more tacticool stocks for the M1A look better to me than the AR-15s and SCARs

May 6, 2014, 01:08 AM
"we're sick and tired of tacticool everywhere"


May 6, 2014, 01:53 AM
so im not the only one who likes the wooden rifles i mentioned before?

May 6, 2014, 02:55 AM
you know, i could provide all these features.. throw out the AR-15 stock, pistol grip, aluminum forearm and fit everything into a wooden or polymer stock like an M14/M1A or an FN49.. doesnt necessarily have to be open-top either.. i could put the bolt up on top of the carrier and make it side eject with the ability to place a rail across the top of the receiver and still have simple barrel changes, and mutli-caliber capabilities.. something not present in any full-stock rifle

If you get the time, think of making something like this: (

In 357 Sig: (

You could take the 4095 and use all existing parts, change the barrel to the 9mm one and ream out the chamber to 357 Sig and still use the existing 40 S&W mags and have a hot new firearm.

That would be a hot selling gun.


May 6, 2014, 03:29 AM
well, actually im also working on a new pistol... well a couple, one im already working on designing which is a break top 357.. already started drawing this one out.. and i also want to work on a semi at some point.. would love a pistol caliber that fired a spitzer bullet so i can justify focusing on making a more accurate automatic pistol.. possibly something based on the luger

May 7, 2014, 03:11 AM
when i was calculating the bolt thrusts of different calibers, i noticed 45acp and 357 magnum both had a bolt thrust of roughly 3,500lbs.. then i recalled many of the .455 webleys were converted to fire .45acp with the use of moon clips.. the webley frame, latch, and hinge are capable of handling that 3,500lbs of pressure on 100 year old metallurgy

i have a full 3D CAD file of the webley mark IV revolver and i calculated the strength of some of the structural components if modern metals with modern heat treating were to be used and these parts are well suitable to handle 3,500

so starting with this as a basis, ive completely morphed the design.. going to use a much better, smoother, lighter trigger mechanism such as those based on colt or smith and wesson lockwork, but im doing something else.. by using un trimmed .357 maximum brass and pushing the bullet into the brass, i will make a .357 magnum gas seal cartridge.. to handle the rearward pressure of this cartridge im designing a bolt actuated by the trigger that will lock the cylinder forward while the trigger is pulled... i will polish the inside of the chamber that the cartridge fits into for easier extraction

end result is a top break 357 magnum revolver with a four inch barrel, gas seal feature that will have a good trigger, and ive also decided to put a short pistol rail on this too.. since its gas-seal i may also thread it for a suppressor as well

this is what im working on now as i take a short break from my rifle design


if you have any other ideas for anything, feel free to discuss them (speaking to anyone)

May 7, 2014, 05:15 AM
Your top break gas seal revolver sounds interesting in a Webley/ Nagant love child sort of way.

Hope it works, because I want a modern top break. I love single action revolvers and top breaks. Don't like traditional swing out cylinders since they swing out the wrong way for a southpaw.

May 7, 2014, 05:23 AM
Your top break gas seal revolver sounds interesting in a Webley/ Nagant love child sort of way.

Hope it works, because I want a modern top break. I love single action revolvers and top breaks. Don't like traditional swing out cylinders since they swing out the wrong way for a southpaw.
well taking all the bolt thrust of the 357 mag into consideration the design will work find.. and it will be fairly modern too, double action, pistol rail under the barre, heck, if i didnt feel like id be ripping off the MP-412 id even consider a polymer frame.. i was thinking of making the break action springloaded though.. push the lever and the whole action breaks open automatically for an even quicker reload.. you could of course easy it open by hand to save your brass

May 7, 2014, 09:09 AM
"Your top break gas seal revolver"
Focus! It's like swinging at a curve ball, man :p. I do think the revolver is a good concept, I've drawn up ideas myself in the past and run bolt thrust and frame stress numbers, but you really need a new thread for that ;)

FWIW, 3500lb seems a bit low for 357. If that's the operating 35000psi figure, you will want to at least double that (if not triple it) for the latch and frame, since you want those failing long after the cylinder lets go. You also want them extremely rigid, which means they will be stronger than needed for pressure.

"a bolt actuated by the trigger that will lock the cylinder forward while the trigger is pulled"
"gas seal feature that will have a good trigger"
I'm not saying it can't be done, but these seem like contradictory goals.

The design I had come up with was either an 8-shot 357, or 6-shot 9mm/45acp*. The barrel was in the 6 o' clock position, with the pivot being 'cannon trunnions' on either side of the barrel so torque on the latch is zero owing to bolt thrust, and solely stemming from misalignment or recoil. There was no top strap, just a beefier-than usual center pin extending from the center of the ratchet which engaged a self-tensioning sliding latch at the rear.

A much more complicated but interesting variant was a short-stroke operated auto-revolver that slide the center axis back a little bit upon firing to impart the needed energy. When it slid back, the self-tensioning latch would loosen, allowing the cylinder to cycle (the cylinder was indexed like a ball point pin with a spline gear, rather than a hand). Another aspect of this action was that the breechface was pushed forward to ram the cartridge and cylinder against the barrel for consistency and gas seal; this was done with two inclined planes wedged against each other in series (the force multiplier was like 5000X or something) to force the breachface forward, and whose combined friction under load (oiled, of course) would resist opening under any amount of bolt thrust (geometry trick). The idea was a pistol that was bound up in every single moving joint at the moment of ignition, which would seem to cure any accuracy issues that top breaks are supposedly prone to due to looseness. It was striker fired, btw, but could be cocked with the break-lever. I estimated cost in the thousands :(


*Short rounds load so much easier and moon clips would be used for fast loading, so auto pistol rounds make as much sense here as autopistols

May 7, 2014, 01:53 PM
im quite on track.. i just like to take a break from one design and work on another in the mean time before going back and i have many, many ideas id like to work on.. feel free to discuss some if youd like?

May 7, 2014, 07:56 PM
's all cool, man. But a new thread in Revolvers or Pistols would get those interested parties involved. I've got a good half dozen gun projects going simultaneously so I don't get bored/burnt out on any one, so I feel you looking at other ideas.

As far as my "Mouse Gun That Roars*," it's a delayed recoil operation. Something that makes perfect sense but has never been tried that I'm aware of. Put too much juice into a recoil operated action and it opens too fast and too hard and will kill itself through either case rupture or slide peening. So let's do the exact thing we do on straight blowbacks that have the same issue; delay the rapidly moving mass through mechanical leverage. Basically, I turn the striker into a massive part that is thrown back faster than the slide during it's initial recoil before unlock, effectively increasing the mass of the slide to extend the range of cartridge energy it can absorb. The rough layout was a standard-shaped slide on frame rails, only with an external striker forming the upper half of it and linked by a frame-mounted lever (1:1.5 advantage for the slide/striker)

For reference, on the attached concept model, the ejection port opening is the size of a 5.7's OAL (1.6") making the rough model about 5" in overall length (grip/magazine might add a little to that) and .8" wide, so I think it could even be a near double-stack. Probably a bit of a hot potato in 5.7x28, even with proper delaying features :eek:, but a real noisy cricket to be sure.


*AKA "the marketing that writes itself" :D

May 7, 2014, 08:14 PM
aah, i think i get it.. but.. what would be the primary benefit of this?

May 7, 2014, 09:29 PM
5.7x28 in something 5" long and .8" wide that won't blow up in your hand. Would also allow much higher-recoiling rounds in pistols of all sizes with less fear of damage or untenable recoil.


May 7, 2014, 11:25 PM
ive never been too impressed with 5.7x28.. it seems to be really underpowered for what it COULD be.. also, the base diameter of the case is a bit odd.. not easy to find brass for.. now what would be really cool is creating a new cartridge based on the .223 case.. basically just shortened .223 down to 40-41mm, youd have more case capacity than the 5.7, same bullets, more power, and you can chop and shape common 223 brass

check out this cartridge.. starts out as .223 brass, then its trimmed and necked down... case length is 28.4mm, overall length of 41mm with a case volume of about .075 cubic inches.. ballistically this would be about the same as the .221 fireball cartridge which produces about 1,000ft/lbs energy in a 14" barrel and would be small enough to chamber in a autoloading pistol.. do the same thing with the same bullet starting with a .308 cartridge (same base diameter as 45acp) and youd have the same case volume as a .223, so balistically your cartridge that would be no larger than a 44 mag would have all the energy of a .223 firing from an autoloading pistol

May 7, 2014, 11:46 PM
It's called 22TCM, I believe. On paper, it's superior to 5.7, but uses pathetically small expanding bullets as opposed to fragmenting long-ogive projectiles. I think 22TCM with the same actual Vmax bullet characteristics as 5.7, but loaded to 223 pressures (would obviously need to be made of the same actual brass) would be incredibly effective, though perhaps not from a very short and light weapon. :evil: The primary reason 5.7x28 can't get much hotter is because it's fired exclusively in blowback and semi-delayed blowback guns (P/S90 and five-seven, respectively). Any higher in lighter platforms, and you get case separation as the case extracts under pressure.

The real shortcoming to 5.7 (that comes with a matching benefit) is the primer pocket is HUGE compared to the case head, so it can swell and loosen under high pressures much more readily than a small primered 9mm, for example. Makes reloading a low-reuse proposition (Teflon coating doesn't help, either). The benefit is the case is narrower (I think) than even a 32acp, making it extremely unique in terms of capacity. The five-seven holds 20 rounds, which isn't that impressive, but this is mostly due to the size the gun happens to be. Though the round may be X% smaller, that doesn't translate into X% higher capacity since we have to round down to the nearest whole round. A mag much larger has significantly more capacity (the 50rnd P/S90 mag), and I imagine a mag a bit smaller would be very high capacity for its size (for example, I'll bet about 10 rounds would fit in my currently 7-round R51 mags if they were .05" longer --that's a nearly 50% increase!)


May 7, 2014, 11:49 PM
"so balistically your cartridge that would be no larger than a 44 mag would have all the energy of a .223 firing from an autoloading pistol"
It would likely be higher, being a stubbier case (read: the WSSM fad a few years back. The portly cases did deliver higher velocities for the same powder/pressures, but the increased case head area rapidly ate up numerous actions' bolt thrust capacity; there's no free lunch, even if you don't care how big your magazines will have to be.)


May 7, 2014, 11:53 PM
oops, i forgot to actually post the rendering of the cartridge, i posted it above

ive looked at the .22tcm, i just wish it didnt try so hard to fit within a 1911 size action while providing little more ballistically than the 7.62x25mm which can be incredibly hot, and much cheaper.. when trying to get as much power into a handgun as you can.. to have a cartridge thats quite powerful in a short 10" or so carbine, you have to make as much use of the spaces you can.. so why limit yourself to a 32mm cartridge when the average hand can comfortable fit over a magazine holding 40mm cartridges?

May 8, 2014, 03:48 AM
you know.. i could use that cartridge above in my revolver.. could even make that a gas seal if i wanted to extent the neck of the case out over the bullet.. imagine that in a revolver

but..after doing a little research it seems this thing will equal the .221 fireball in performance out of similar barrel lengths, which in itself equals the .223 in 14 inch and shorter barrels (where the 223 just blows the excess powder out the barrel anyway).. so this cartridge in a 10-12" carbine would perform about the same as a 10-12" AR-15 and surpass the 5.7x28 in a pistol.. would be great for a PDW and sidearm of greater performance to the 5.7, and much easier to get ammunition since its just made from 223 brass

this may sound odd but i actually had a dream where i was using the cartridge shown above in a carbine like the one shown by jim on the last page that took magazines in the grip

May 9, 2014, 07:18 PM
the second rifle design i was working on.. not the one ive been discussing here but a short-recoil model ive been working on ive decided to stop working on.. its operation would be too similar to this pistol/pdw/carbine idea im working on now since it too will be short-recoil.. but i think ill start a separate topic in the autoloading pistol forum

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