focus group for a new modular rifle design, which features would you like?


July 29, 2012, 04:52 AM
hey everyone... im working on a new rifle design of my own.. but this time, im aiming for a modular design that when finished im going to register and file as being "open source" meaning when the prototypes finished and tested, all schematics, blueprints, and specs will be freely available for anyone to manufacture...

so im looking for ideas as to what you would like to see for a fire control group, furniture, charging handle, gas system, magwell.. and just which parts of these should be modular?.. as well as any other parts or features i havent mentioned...

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July 29, 2012, 07:49 AM
I like gas piston operation.
If you could muster a good FCG and trigger, a bull pup with adjustable stock.
Furniture should be impact resistance polymer, forged aluminum receiver.
Two stage trigger, adjustable.
Flared magwell, like to see it use AR-15 mags but chambered in something more potent, such as 6.8, 308, or even .243 win. Probably go with a non proprietary design or AR10 stuff.
Rapid change barrel, none of that barrel nut stuff.
Threaded barrel, length undetermined.
Ambidextrous options for side charging handle, or assimilate the AR charging design. Rather side charge personally.
Free float handguard, options for rail sections for lights, lasers, optics, fore grip.

I tried.:)

July 29, 2012, 04:17 PM
what im working on now, the receiver and forearm are one piece for a full length top rail, abidextrous polymer lower with stainless steel blocks imbedded into it for areas that would see more stress... for the barrel, im thinking of designing a quick change barrel extension that could fit threaded barrel blanks... the locking lugs and chamber would be in the extension, so no headspacing required

as for gas system, i was actually going to have a removable piece on the carrier and the gas block that would allow someone to change out gas systems... with pieces available for direct impinged, short-stroke, and long stroke piston... on the carrier where the piston would go im going to have a depression drilled into it, so that either a cup, a striking plate, or a piston itself can be put in the front of the carrier, and fixed in place with a screw or pin, similar to how the AKs gas piston is installed..

those are just some ideas ive thought up, and ive also been thinking about a removable magwell if i can decide whether it should be fixed to the upper receiver, or as part of the lower

another idea was to have two ejection ports, the one not being used would aid in blowing out heat and crud from the receiver, and would eject straight out the side... end user can remove the bolt, remove the cam block, insert it into the opposite side and reinstall to eject from the opposite side of the rifle

July 29, 2012, 07:05 PM
A side charging handle sounds good. I became very accustomed to that shooting AKs and SKSs, but started shooting an AR. After that I can see the advantage of a charging handle that doesn't move with every cycle. Possibly incorporate a side charging handle that acts like one from an AR.

July 29, 2012, 09:53 PM
maybe one like the israel FAL which had a non reciprocator that could function as a forward assist as well by pressing it in... and be able to be switched to either side?

im actually wanting to put on interchangable magwells, one idea i had was to use an AK-47 magwell, with an optional STANAG magwell adapter... i havent decided if the magwell will be part of the lower, or the upper yet.. but im leaning towards it being part of the upper, have it pivot where the front of the trigger guard mounts behind the magwell

also, would you (anyone reading) prefer the stock to be part of the upper, where the stock pops off and releases the lower to pivot out of the way for a field stripping, or have the stock as part of the lower with a captive takedown pin (like on the AR)

July 29, 2012, 10:20 PM
Long sight radius - front sight at the end of the barrel, rear peep back close to the eye.

Serialed lower for easy purchase of uppers to facilitate caliber change.

Interchangeable magwells to accept multiple mag types - AR15, FAL, AK47

Fully ambidextrous controls - bolt release, mag release, safety.

July 29, 2012, 11:28 PM
All of the current offerings have gotten very close to addressing all the needs of a modern tactical carbine, but none have addressed them all while including the caliber modularity aspect of it, either due to cost, lack of foresight, inadequate testing, etc.

For a myriad of reasons, the FNH SCAR, Remington/Bushmaster ACR, Robinson Armament XCR, Colt CM901, MGI Hydra, CZ 805 Bren, Beretta ARX160, and other current next-gen modular carbines all seem to fall short of perfection, at least according to the "experts" anyway.

The big problem seems to be barrel/caliber change and loss of zero, requiring you to re-zero your sights/optics every time you change caliber. The CM901 tries to address this by making the whole upper the part that changes, so you can have a dedicated optic for each upper. But that's heavy, bulky, and expensive. It seems to me that there could be a great compromise somewhere in between that no one has really attempted. If Larue and GG&G can make optics mounts that can consistently retain zero after multiple attachment/detachments, then one ought to be able to do the same with a long segment of picatinny rail that not only acts as the sights/optics mount, but also as a dust cover (not like an AK).

I will try to describe what I'm thinking as best as I can since this is open source.

Imagine an FN SCAR. Imagine that the top rail is fixed to the barrel in a similar way to how the bottom rail already is. The top rail is attaches at the rear of the receiver to lock in place and act as a dust cover. The whole thing slides out the front. Do away with the tilting upper/lower by making the trigger group and mag well detachable and have the bolt carrier group come out the rear much like the ARX160. Also give it the selectable ambidextrous ejection port like the ARX160.

Combine the above with a bolt release like the ACR, fully ambidextrous safety, left and right non reciprocating charging handles that can act as a forward assist, and a slightly longer forearm to accommodate the latest shooting stances as well as taller folk and in my opinion you might just have perfect ergonomics and full modularity all the while not worrying about zeroing in every time you change caliber. Keeping the weight down would be tough.

Just some ideas.

See the attached picture

July 29, 2012, 11:40 PM
Yes it does sound like the SCAR but the bull pump design is more like the FS2000


July 30, 2012, 12:45 AM
does the scar already have this feature?... i was planning on using a barrel extention that would be pre-headspaced and contain the locking lugs, this would allow any threaded barrel blank to be threaded into and fixed into the barrel extensions.. these barrel extensions would quickly connect and disconnect from the upper...

what i could do is cut a groove in the top of the upper, like a dovetail that the rail would slide into, and a piece that extends into the forearm... does the SCAR already have this feature or was that something you photoshopped?.. its a good idea and one i would certainly use... ill add that feature because its a very good one..

ive also planned on adding the selectable ejection port.. i want it so that lefties can have this rifle, and adapt it to being an entirely left handed rifle if they choose

.. for the magwell i was thinking of having some grooves machined into the side that a magwell could be slid over, or off of that would allow interchangable magwells... maybe have the trigger group slide over it onto the same rail... then have a vertical rail in the rear for the stock to slide onto, holding it all together... takedown would be press a detent and slide the stock down and off, then the trigger group, magwell, and carrier can all be removed off the back... barrel removal will either be some kind of lever system, or more likely a detent-locked thumbscrew (detent prevents it from backing off)... similar to how the SCAR and XCR uses a screw for the barrel.. except the thumb screw would require no tools and be mounted under the lower handguard so theres no chance of hitting it on anything either

im still looking for suggestions on takedown, how all components fit together, and the quick change barrel feature

any suggestions as to how the removable magwell and trigger group should fit with the upper, and how the stock should be fixed to it?

July 30, 2012, 01:15 AM
It's something that I did in ms paint to illustrate what I was trying to describe. Attached is a photo of how the SCAR barrel normally looks when it's removed. It's just the barrel, the extension, the gas block, and the bottom rail. The whole top rail thing is what I was trying to suggest in order to be able to attach a caliber dedicated and zeroed optic without having to buy an entirely new upper.

July 30, 2012, 04:29 AM
yeah.. i knew what you meant when you described it and its a very good idea... you could sort of route a dovetail in the upper receiver for the picatinny to slide into.. cut a slit in the top of the forearm for the rail to slide into as well and your extended rail will all be fixed to the barrel extension and maintain zero... so ill add that to the design

July 30, 2012, 08:30 AM
It sounds like you're defaulting to a rotating AR-type bolt, which makes it necessary to have a barrel extension to lock into with a QD barrel. You could lose the need for a barrel extension if you used a tilting/dropping bolt instead, like the BAR/M240 or Bren.

Also, if you want this to be something a decent home shop can manufacture, you should stay away from forged parts. Design the components to be simple to set up on a CNC machine - keep radii to a minimum, and minimize the number of fixtures needed for each part. Nice simple stampings would be a good way to go too. Castings and forgings are a lot more expensive for small-scale production. (

July 30, 2012, 02:13 PM
It sounds like you're defaulting to a rotating AR-type bolt, which makes it necessary to have a barrel extension to lock into with a QD barrel. You could lose the need for a barrel extension if you used a tilting/dropping bolt instead, like the BAR/M240 or Bren.

Also, if you want this to be something a decent home shop can manufacture, you should stay away from forged parts. Design the components to be simple to set up on a CNC machine - keep radii to a minimum, and minimize the number of fixtures needed for each part. Nice simple stampings would be a good way to go too. Castings and forgings are a lot more expensive for small-scale production. (
i have been thinking about this as well, making it rather simple for someone to build themselves.. and actually, the simplest way i can think of to have a monolithic upper with a forearm as part of it with a full rail was to form the upper on a shop press.. shaping the top of the receiver, and top half of the forearm as a rounded section, bottom half of the forearm would be removable, and the remaining part of the receiver section would be straight, bent at the bottom and welded along the seam...

then i was thinking of having the rail spot welded to the bottom edges of this for the magwell and trigger group to slide onto

point of the barrel extension was to employ a quick change barrel feature, allow the end user to use any threaded, unchambered barrel blank for a barrel, requiring only the drilling for the gas block and the pins to hold it, as well as to support the top rail which will be part of the barrel assembly, so you will not lose zero when swapping barrels

at this point though.. im still trying to determine how the magwell and trigger group will attach... im not 100% sure im going to have them slide onto a rail from the rear... i may have the front of the magwell hook onto something on the outside of the receiver, and snap in, similar to the way an AK47 magazine hooks into its magwell which just require a riveted portrusion on the sides of the receiver and an AK style latch to hold it in place

reason i was avoiding hooking the magwell to the trigger group was that the magwell might end up with a little play to it after so much use... trigger group would do the same as parts wear, you would get even more play if they werent both connected directly to the receiver itself... so im thinking ahead on that part

one other thing im debating is whether this should be a .223 length action, capable of firing 5.56mm, 7.62x39mm, 6.8mm SPC, and anything else that can go into an AR15.. or if i should make it a .308 length action with a standard AR15 type magwell for the option of changing calibers between 7.62x51mm and 5.56x45 and anything else that would fit in it

July 30, 2012, 03:14 PM
I want something designed to accept top-notch factory peep/aperture sights and a scope. I don't know if this means it should be designed with a side-mount for the scope, if the aperture should be side mounted, or what-have-you. I don't really like any of the ideas that I come up with, so maybe a real focus group bent on designing something special could be more innovative/creative.

July 31, 2012, 02:31 AM
well.. ive been working on this design some more.. .seems the top rail mounted to the barrel extention will work just fine... im not going to have a monolithic receiver afterall.. ive decided against this for a couple reasons...

first reason, monolithic doesnt really add much i cant get by other means... so, the barrel extension which will be permanently fixed to the threaded barrel blanks in the caliber of your choice will have a full length top rail that will stretch from the rear of the receiver itself, to the barrel extension, and be supported on the top of the gas block as well.. this will all be one long flat rail thatll remain constant with the barrel, therefor, it will never lose zero

the upper receiver is looking more and more like its going to be simply a piece of rectangular tube steel and will either have rails spot-welded to the inside.. or be pressed into the sides with a shop-press

its going to need a trunnion.. this trunnion will not serve any other purpose than holding the barrel extension in a quick-changable manner, which is either going to be a lever, or even simpler, a detent-locked thumbscrew

rear of the gas block is going to be threaded, so that a gas tube for either a long stroke, short stroke, or direct impingement tube can be fitted to it.. and there will probably be an adjustable regulator adjustable from the front

where the piston would come out of a bolt carrier normally, it will be drilled out with an endmill and threaded which will allow either a striking surface for the short-stroke system, the piston for the long-stroke system, or a cup for the DI system to be installed by threading it in.. then driving a set-screw or pin in place to hold it

the fire control group at this point will be that of an AR15...

there will probably by lips on the bottom of the receiver thatll hold the magwell and trigger group but this is still not 100%... it will however probably end up being a 7.62x51mm length action that can accept a 5.56x45mm STANAG magwell or an AK type magwell... this will give the option of changing to any caliber that would fit in a .223 or .308 action, so 6.5 creedmor, .243, and the short-magnums would be possible with the longer magwells

my issue so far is that the im not sure how secure the magwell and trigger group will be to the receiver... im debating whether sliding them over a rail, and having a ball detent lock them in place is going to be secure enough to hold tight and not wobble..

so im looking for ideas on making the magwell, trigger group, and upper receiver all fit together, as well as possible mechanisms for quickly removing or installing the barrel assembly into the trunnion?

August 1, 2012, 04:58 AM
someone mentioned the idea of a tilting block setup... im not sure if a titling block will hold up as well over a longer period of time.. by that i mean it seems it might lose its headspacing over time as the surfaces wear down.. and i dont think rotating bolt is all that hard to machine at home.. however, i would entertain the idea of a breach block mechanism if it were to lock closer to the chamber so it can be oart of the barrel itself

August 1, 2012, 10:22 AM
I have posted all my ideal features for a self-loading rifle before, but I'll post them again. Some you already suggested, but I differ on some.

- AR-type barrel extension and nut, for easy, no-headspace-required re-barreling
- AR-type modular receivers, for easy take-down and swaps
- Picatinny railed upper receiver, for easy optics mounting
- Handguard separate from receiver, to allow use of different lengths and styles
- Left-side (or ambi) charging handle
- Short-stroke gas piston, as a compromise between clean shooting and low mass
- Adjustable gas block
- Long sight radius, with front sight at the muzzle (rear sight to be mounted on receiver rail)
- Mags that insert straight in and drop free
- Curved magazines and mag well, for reliable feeding (not an issue if you use interchangeable mag wells)

I disagree with the receiver and handguard being one unit. Then you are stuck with whatever handguard it comes from the factory with. You see this problem with the FN SCAR, where the factory handguard is a stubby little thing that is fully railed. If you prefer a longer handguard, and/or one that is modular instead of quad rail, you are out of luck. Also, it limits the rifle to a certain length gas tube, leading to the ridiculous 20" barreled rifles with stubby carbine-length handguards and gas system. IMO, removeable handguards are a big part of any rifle which purports to be modular.

Also, I don't see how it would be a benefit to be able to use different types of gas systems (long stroke, short stroke, DI)... as long as it works reliably and shoots well, who cares? I say just pick one, and concentrate on making the rifle work as well as possible with it. As I said, my preference is short stroke, since it allows for a fairly light reciprocating mass as well as having the benefit of running clean. But I wouldn't turn my nose up at a reliable and accurate long stroke or DI rifle, either.

Shawn Dodson
August 1, 2012, 10:44 AM
The ability to lock open the bolt with one hand for clearing stoppages.

A side mounted charging handle (I'm right-handed so one I can operate with my left hand) that reciprocates with the bolt. This way I can transfer my manual of arms directly over from my pistol (Tap, Roll & Rack) without a lot of slack in the charging handle if the bolt is out of battery due to a stoppage or it's locked open.

A manual safety similar to a 1911 that can be easily manipulated with my firing hand thumb without disturbing my firing grip.

NOT a bullpup design (for better manipulation ergonomics).

An open top action design (e.g., M14 type) as opposed to one that's completely enclosed with an ejection port on the side (e.g., M16 type) to facilitate ease of quickly clearing stoppages.

August 1, 2012, 04:56 PM
ive actually been thinking about the fixed handguard idea.. and if the rails for the top of the receiver are part of the barrel, instead of the receiver itself (so optics remain zeroed).. with an extended rail for the top of the forearm, i wouldnt actually need a fixed forearm... monolithics are for that one piece rail, this will supply a one-piece rail but still be able to swap out forearms that will be free-floating, mounted to the rail

ive been thinking of the quick change barrel feature.. i can use cammed pins in the trunnion to grip the rim of an AR15/AR10 type barrel and hold it securely, similar to how the MGI QCB works for the AR15 (i think thats how it works)... im trying to find out exactly what locking mechanism will be used... i could simply, and rather easily machine the trunnion to take AR10 or AR15 barrels (since i want the max magwell length to be able to accept .308 magwells, probably the AR10 barrels)...

the AR10 barrel extention contains threads in it to use a threaded barrel... so barrels similar to those used on bolt actions would be fairly easy to find and offer the ability to fire any caliber thatll fit in the receiver... besides being able to fit a threaded barrel in it, the extension has the locking lugs as well.. so the custom barrel and barrel extension would have to be headspaced, but once headspaced theyll remain a pair for the life of the barrel, and its the extension itself thatll be quick to interchange (if this makes sense)

which means the bolt will have to use AR10 type locking lugs and be rotating bolt

obviously, the receiver can be made different ways... rectangular tube steel spot welded to the trunnion like the way an HK91 trunnion is installed, simply machining the trunnion receiver, and rails together as a milled piece of steel or aluminum, one idea i had was to machine stainless steel pieces for high stress areas, and place them in an injection moulding machine for a strengthened polymer structure... which is fine for the lower and magwell, but id have to be certain internal temperature was low enough to consider doing it for an upper

August 1, 2012, 05:00 PM
oh.. when this is finished.. i do intend to upload some rendering photos to show what it all looks like...

also, the carrier itself will have a groove for a non-reciprocating charging handle, but a hole that goes a bit deeper so you can press this charging handle in and use it for forward assist, and im also working out a simple way of fixing it in this position so it can be used as a reciprocating charger as well

August 1, 2012, 08:10 PM
Trigger reach for man sized hands.

August 2, 2012, 02:11 AM
Trigger reach for man sized hands.
i do plan on having a little more space in the trigger guard than a lot of rifles offer.. i live in cold areas and would like something that works well with winter gloves

Andrew Wyatt
August 2, 2012, 05:45 PM
an option for a non PG stock.

August 2, 2012, 06:05 PM
mid-length gas system
piston driven
interchangeable barrels (like the DTA sinper rifle)
the ability to charge the weapon, change mags and operate all controls without breaking cheek to stock.
ambidextrous everything.
ability for multiple calibers.

August 3, 2012, 07:36 PM
As for the bolt carrier, i would suggest minimizing contact with the receiver for reliabilty. and for the piston, try to make the grooves easy to clean, avoid deep cups like an M249 SAW piston. and perhaps if possible, you could clean dirt and residue from the rifle by simply submerging it into water and shaking it.

Ky Larry
August 4, 2012, 10:30 AM
Make it affordable.

August 4, 2012, 06:33 PM
well, so far it seems like everything people have said they wanted can be achieved with this single modular design im working on... when its finished... completely finished ill register the design as open source and post the blueprints/schematics and 3D solid-modeling files

August 4, 2012, 06:40 PM
I like the sig 556 operating system, rock river arms fire control group, collapsible folding stock, picatinny rail sytem built into upper assembly, ability to chamber 5.56 and swap for 308 would be good. Most of all make it affordable and lightweight with an 18" barrel.

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