designing a rifle and would like some input

[barnbwt]

"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)

TCB

*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.

 

[justin22885]

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

 

[barnbwt]

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.

TCB

PS:
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 )

 

[justin22885]

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?

 

[barnbwt]

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.

TCB

 

[justin22885]

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

 

[barnbwt]

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.

TCB

 

[justin22885]

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

 

[barnbwt]

"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.)

TCB

 

[justin22885]

does the g36 use the sort of tappet piston as well?

 

[barnbwt]

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 (or perhaps Keurig coffee maker technology )

Extremely interesting and technical article on the CZ805 BREN's development, operation, and introduction;
http://sadefensejournal.com/wp/?p=1083

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...

TCB

 

[justin22885]

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?"

 

[barnbwt]

'fraid I can't give you too much advice, except so say that an open-top bullpup probably won't fly

"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

TCB

 

[justin22885]

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

 

[justin22885]

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

 

[barnbwt]

"we're sick and tired of tacticool everywhere"

TCB

 

[justin22885]

so im not the only one who likes the wooden rifles i mentioned before?

 

[jim243]

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.

Jim

 

[justin22885]

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

 

[justin22885]

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)

 

[USAF_Vet]

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.

 

[justin22885]

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

 

[barnbwt]

"Your top break gas seal revolver"
Focus! It's like swinging at a curve ball, man . 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

TCB

*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

 

[justin22885]

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?

 

[barnbwt]

'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 , but a real noisy cricket to be sure.

TCB

*AKA "the marketing that writes itself"