technical discussion for the function and design of self-loading rifles

[jason41987]

hey everyone.. im just making this thread for myself, and people looking to debate the various aspects of a self-loading rifle... different types of actions (blowback, recoil, gas), different materials, construction methods, calibers, etc....

i would like to know what you would think of as the perfect semi automatic, if in your own image you were able to design one?..


---

first off, i would like to know other peoples opinions and feelings about gas operated (long and short gas piston systems), recoil operation (long, like a browning auto 5, and short like a johnson 41, or handgun) as well as blowback, standard blowback, and the various delay mechanisms such as roller, and lever delayed... and for gas and recoil operated systems, what type of locking mechanism do you like most (rotating bolt, tilting bolt, etc)

what do you think would be the best operation in your opinions and why?

---

i would also like to know what type of feeding mechanism you think is best.. box magazine, internal or external... helical, rotary, belt, as well as what magazines of already existing rifles you like most?.. ar-15 mags, AK mags, etc..

---

im also curious what you guys think about one piece furniture such as those used on the garand, M1A, mini-14, and SKS, vs the seperation of forearm, grip, and stock such as those on the AR-15, AK, FAL, ect

---

i would also like to know how you feel about the different calibers available... if you prefer lighter, more plentiful ammunition, such as 5.56 or 7.62x39, or if you believe the added range and stopping power of a .308 to get more done with fewer rounds is the better way to go?

---

and lastly, if anyone else could think of any other features or ideas, feel free to discusss them

 

[45_auto]

There is no "best" of any of the items you mentioned. Every one of them is a compromise, and the "best" will depend upon the specific scenario you are tasked with or wish to discuss. Every one of them is "best" at one thing, and worst at something else that one of the others is "best" at.

Good luck with your discussion!

 

[jason41987]

oh, i know the pros and cons of different designs, been working on various ones in 3D, i was looking for opinions and discussions on the different types...

for example, blowback design, such as lever or roller delayed is a very simple design resulting in a lighter rifle, however, the bolt does move prior to the bullet leaving the barrel, and is dirtier in general.... but without a long gas system, the bullet is usually already out of the barrel before the gas enters the tube and acts upon the piston/carrier, and is easier to fine tune, and less picky about load pressures

 

[briansmithwins]

Start off by reading Chinn's The Machine Gun, all 4 volumes are available online in .pdf.

(If you run into Vol. 5 send me a link, I haven't read that one yet.)

Yes, all self powered firearms are a series of design compromises. What will blow your mind is that pretty much every way of carrying out the cycle of self loading was invented before WWII.

The other interesting item is that there are only two ways of designing a self loading firearm: gas operated and recoil operated.

Blowback? The cartridge case is a one use gas piston, forcing open the bolt.

BSW

 

[jason41987]

this thread is to further discuss the tradeoffs, whether you may thing one tradeoff is worth another and so forth...

and about most systems being designed before WWII... we had a service rifle for just about every action in service at one point or another during WWII.... bolt action in the 1903, long stroke piston in the garand, short stroke piston in the carbine, blowback in the thompson, and even short-recoil operated in the 1941 johnson rifle...

ive actually designed a few rifles myself in 3D.. but of course they use one of these features or another... the one im working on now is a .308 caliber lever-delayed blowback that once finished will look similar to the M82 barrett rifle, but scaled down and obviously sharing zero features besides general appearance (entirely by chance)

 

[henschman]

The perfect rifle for me would be a short-stroke gas piston operated rifle with the barrel mounted with an AR-15 style barrel extension, the stock in line with the bore, a flat top picatinny rail, a curved magazine well with drop-free mags, either a chrome lined or nitrided bore, chamber and gas piston, an adjustable gas block, a front sight attached to the end of the barrel right at the muzzle, lightweight modular handguards, and chambered in a nice high-BC, intermediate power, tapered-case cartridge like .280 British.

The reason I like a short-stroke gas piston is that it can work just as reliably as a long-stroke gas piston action, but it has less reciprocating mass, which helps with accuracy.

 

[Tirod]

And, DI offers even less reciprocating mass - but there's a limit, or it becomes too light to reliably strip the first round. Bolt bounce becomes a problem if you speed it up.

Compromises entail finding the optimum middle ground of operation.

Let's not forget how the barrel is attached the receiver, too. In that regard, the Stoner design offers a lot of versatility, as it eliminates the receiver - barrel attachment and reduces it to a bolt lug extension only, which screws on and adjusts the head space much like a micrometer. No press, no fuss, no muss.

Entirely why you can build a highly accurate AR on the kitchen table. Literally. And part of why they have run off piston operated conventional receiver actions in precision shooting.

Choosing from a menu of different features is fun, but the combined affect of their dynamic operation is where the results are seen in the target. The operation of the firearm as a whole, in the hands of the user, is far more significant than a casual discussion of what individual feature might be better.

 

[jason41987]

im designing a rifle of my own right now in 3D... uses a long piece of steel tubing that makes up the upper receiver, forearm, and part of the stock... so in the end itll probably end up looking like a scaled down m82 barrett...

currently, im stuck on a couple features.. im not sure if i want to make it top eject, or side... my goal is to make it ambidextrous... one idea i had was to cut an ejection port in each side... then when it ejects the round, the other side will be open to to help blow out fouling, and possibly debris... my other idea was to make it top eject...

this design as it stands is a .308 semi auto rifle, lever-delayed blowback, but the lever itself is under spring tension to delay blowback, this allows the lever-delayed system to be adjustable...

however, springs do break, and should this one break, the lever wont work, and should that happen it wont lock up... so with this in mind im currently working on a failsafe, and the way im going to do this is the other side of the spring will press on a lever that holds open a firing-pin block... if spring tension is for some reason lost, the firing pin block engages and prevents the rifle from being fired...

chances of the spring itself breaking is incredibly slim, like winning a lottery slim... but doesnt hurt to plan ahead for that possibility and find a way for it to fail safely...

if made to be top eject, my idea is to cut slits in the side of the tubing for the rails, and use T shape pieces of steel slid into those cuts, and welded from the outside after the sides of the T are bent around teh receiver... this does two things, gives me rails, and greatly increases the strength and rigidity of the receiver

since the receiver is mostly a piece of tubing, no guide rod is needed, the recoil spring will just equal the inside diameter of the tubing... and the front trunnion itself will have a piece extended below for the fire control group to be pinned on to..

at this point im just going to use a fire control group that can be purchased online, like an AR-10 group, or tapco AK trigger setup

and as of yet, i have decided where the magazines will come from, i really like the AK-style rock-on magazines, so possibly saiga .308 mags

havent decided yet if the magwell will be part of the upper, or part of the lower

---

id love to hear comments and questions about this idea, fun to design things in 3D and discuss them

 

[jason41987]

i really like the AR-15s barrel setup.. how they attach that barrel is very nice... ive considered using a similar means... would be cool to use AR-15 / AR-10 barrels.. i may have to consider incorperating that into my design...

ive also thought about eliminating the barrel shroud extending from the receiver, and just extend and thread the trunnion beyong the receiver, and get another piece of tube steel to thread.. then just screw it over the trunnion for a completely free-floating forearm, with the option of switching out forearms as well.... i was already going to use AK style pistol grips, since theyd mount more easily to the bottom of the trigger group than the AR-style

 

[Autopistola]

I'm glad you're thinking outside the streamlined box, and giving thought to a simple chassis. I am very interested in various methods of delaying the action. Everything for rifles is going the way of the rotating bolt, whether for accuracy or ease of manufacture.

Lever-delayed is very neat and I often wondered why it's not in more small arms than the FAMAS. I also like the tilting-block designs, like the VZ-58. I don't really have much technical info to add tho, I know many on here a far more knowlegeable than me.

I agree with Henschman in post #6 and would like to add modular design and easy disassembly like an AR.

 

[Rail Driver]

Keep in mind that springs are considered "consumables" - they're GOING to break. Some springs are viable for thousands of cycles, and some springs are viable for hundreds of thousands of cycles, but eventually they all weaken and break.

 

[jason41987]

yeah rail driver, which is why im finding a need to develop a means for it to fail safely if a spring fails... maybe add redundancy with two levers, two springs, and have it set so if one fails, the other is still good enough to allow function...

but i was going to have the spring, when the lever is installed on the bolt add tension to a firing pin block.. once the spring breaks, tensions gone, firing pin block locks the pin in place...

HK91 uses rollers instead of levers, and i believe their rollers are spring loaded too, but they do use two of them... so it would be similar to an HK rifles delayed system, just with levers that hook into a groove inside the trunnion

---

im also going to work on a gas powered rifle when this is finished... umm, actually, the only other rifle im aware of with the action im looking at is the old STG 44...

ive put a lot of thought into the type of gas system i would want most, and come to the conclusion that rotating bolts tend to be stronger, more reliable, and less likely to jam from dirt or debris, so id go tilting bolt.... also, i like the tradeoff the long-stroke piston offers with the piston riding the bolt carrier all the way back... if something gets in the way of the carrier on a DI or short stroke system itll fail to extract, and jam

 

[henschman]

Yes, definitely a modular upper/lower design, and I forgot to add a left side charging handle.

 

[jason41987]

what are you definitions of modular? what would your requirements be for a modular design?...

henschman, with my design i intend to have a charging handle that can be easily removed and switched to either side... i wont design something thats not ambidextrous

 

[Cosmoline]

What about downward ejection and top-mounted magazine? Gravity assisted feed is pretty reliable , as witnessed by the Owen Gun, Lewis Gun, DP-28, etc. And downward ejection makes it a lot easier to swap right or left handed. In messing around with AR and M1A designs, I'm discovering that the bottom-up magazine feeding often presents the most reliability problems.

 

[Rail Driver]

What about downward ejection and top-mounted magazine? Gravity assisted feed is pretty reliable , as witnessed by the Owen Gun, Lewis Gun, DP-28, etc. And downward ejection makes it a lot easier to swap right or left handed. In messing around with AR and M1A designs, I'm discovering that the bottom-up magazine feeding often presents the most reliability problems.

Top mounting a magazine, unless it's spring driven and horizontal like the P90 mags, is going to seriously limit the sighting/aiming possibilities.

 

[Cosmoline]

It's a challenge, for sure. But it can be done. These were after all some of the most popular and successful small arms ever fielded. We're just not used to top mounted mags these days.

 

[briansmithwins]

ive put a lot of thought into the type of gas system i would want most, and come to the conclusion that rotating bolts tend to be stronger, more reliable, and less likely to jam from dirt or debris, so id go tilting bolt....

Huh? You're postulating all these advantages for rotating bolts and then decide on tilting bolt?

The main advantage of rotating bolts is that they offer very good primary extraction. Secondary, you can reduce the size of the barrel extension by using a front locking rotary bolt. A rear locking tilting bolt is going to require more steel as the locking area is further away from the chamber.

Not a lot of new delayed blowback operated weapons have been developed since the 60's. Problems include sensativity to variations in ammo and a tendency to mangle brass as they all allow the bolt to move while cartridge pressure is very high. Delayed blowback weapons are also going to require either a fluted chamber or lubricated cartridges to keep from tearing the cartridge apart.

If I were designing a rifle class weapon I'd stick with gas operation with a adjustable regulator (like the FAL) and a rotating bolt.

BSW

 

[jason41987]

a top mounted magazine could work... but it couldnt be a typical box magazine, that just gets in the way.. perhaps a helical magazine would work.. especially if its mounted on the top of where the buttstock would be, sights wouldnt be too bad either... and i guess someone could always scale up a P90 mag and find a way to use it... but ultimately helical will probably hold more ammo

it just seems so much easier to eject out the top... it was used on rifles all the time way... thompson i believed was top eject, russian PPSH was, MP40 was angled at the top, garand is sort of top eject, various lever actions were... as long as you didnt have some 24 inch long scope you had to mount i doubt youd risk any rounds hitting your optics...

side ejection is a must with modern gas-operated rifles since the gas pistons usually in the way... but i guesss you might be able to get away with top-ejecting a short-stroke or DI system...

i guess the key that should be focused on is comfortable magazine changes.. not having to reach into any akward position to change it, reliable feeding of course, and secure seating...

one reason i like the AK style magazines is you hook them in and rock them back, they seem to seat more securely, where with the type you pop into the magwell ive noticed sometimes you have to smack them to get them all the way in...however, magazines that drop right out with the push of a button or lever with your index finger is certainly useful for a fast reload

more tradeoffs i guess

 

[jason41987]

i already have one gas operating rotating bolt that ive designed, theres not much to them... with the rotating bolt design i had... i designed it in a way that you could remove the bolt from the carrier, turn it upside down, and re-insert it, causing it to eject from the opposite side of the rifle... then i had an ejection port on each side.. with the bolt closed, the bolt block anything from getting inside, and once opened to eject a cartridge, the other port aided in more airflow for cooling, but had a dust cover you could close for dirty, dusty situations

 

[Rail Driver]

i already have one gas operating rotating bolt that ive designed, theres not much to them... with the rotating bolt design i had... i designed it in a way that you could remove the bolt from the carrier, turn it upside down, and re-insert it, causing it to eject from the opposite side of the rifle... then i had an ejection port on each side.. with the bolt closed, the bolt block anything from getting inside, and once opened to eject a cartridge, the other port aided in more airflow for cooling, but had a dust cover you could close for dirty, dusty situations

I'm having trouble envisioning this in my head - have you actually built a working prototype of this or is it just a 3d model/blueprint?

 

[henschman]

By "modular," I just mean that the upper can be quickly and easily separated from the lower.

 

[jason41987]

no prototypes yet, just 3D design and simulations...

and to hesch... isnt a seperate receiver/trigger group pretty standard on most rifles?.. heck even the garands trigger group/magazine seperated

its so hard to say how well a lever-delayed blowback will work, since i can only think of one example out there.. the french FAMAS, other than that, roller delayed on the HK and a couple pistols seem to build an incredibly reliable, very accurate rifle... but it is true the chamber does need to be fluted for reliability, and partial extraction while under pressure could damage a case..

im also working on another idea that uses a floating chamber which doesnt have those issues... the way this works, is theres a breachplug in the barrel extension that holds the cartridge, when the round is fired, this extension is pushed back like 1/10th of an inch then stops... the momentum causes the bolt to continue moving backwards to extract the round and cycle a new one working like a short-stroke piston, with the chamber itself acting as the piston... and since the chamber only moves 1/10th of an inch, it remains within the barrel extension and the gasses remain in the barrel

 

[jason41987]

hmm

 

[jason41987]

im going to finish up this lever-delayed blowback design and then work on the floating chamber design a bit, i could maybe render some of the final products if anyone wants to see a photo of what it may look like?