I'm designing my own gun! (WIP)

[Davey]

Before I begin, I'd like to give a big thanks to the guys at FirearmFiles.com and CNCguns.com for providing me with the non-parametric models and detail drawings I needed for this model. Many of the drawings were in terrible condition, but they were legible enough for me to create my own model from them.

The stock, and some of the bolt parts are simply Non-Parametric IGES Solids pulled from FirearmsFiles.com, but I've been creating my own parametric models based on them. Everything else - the barrel assembly and parts, gas tube, lower, upper, trigger, trigger guard, forearm, and most of the bolt carrier group have been created from scratch, from the drawings.

Oh yeah, and the railed forearm is also my design as well. It's just been superimposed on the barrel nut, I haven't actually figured out how I'm going to attach it just yet, if I'll be using it at all.

Here's the entire system. Shown here is the semiauto model only, with a semiauto bolt carrier group, although note that the trigger (which is an AR-15 trigger that I also modelled myself) has an notch cut in it for the full auto disconnector. I couldn't be assed to make different ones.

From the other side, minus the stock, gasblock, and impingement tube...

Sectioned.

Closeup of the gas impingement system. When I sat back and looked at it presented in 3D from this section view, my first thoughts were "Wow, Eugene Stoner sure thought of everything." Look at the little gaskets around the bolt. Not only does the gas push the carrier group backward, but it also eases the bolt forward a tiny bit to aid with it unlocking. I never noticed that until now. Note that in this picture, the cam pin is out of position - I was fiddling with the assembly constraints when I made this, so it's not where it should be.

High Quality rendering of the AR-15 Lower Receiver, or at least the semiauto one.



Since every guy, his little brother, his grandma, and her dog are out making AR-15s, I've been thinking I might do something a bit different instead of just making another AR-15 type. So, what I'm going to be doing is following the same procedure that Magpul did when they created the Masada/ACR - I'll start with the basic AR-15 design, then slowly start trying to evolve whatever I like in and don't like out. So what I'm probably going to end up keeping would be the fire control group, some parts of the bolt and carrier, and a bit of the lower. The rest I'll probably do away with or evolve out.

So far, here's my little list of to-dos. As I was creating the model, I looked at different things and asked different people I knew about their opinions on how to go about it.

• Implementation of dual self-regulating 'shut off and expand,' short-stroke gas pistons with non-reciprocating inertial operating rods. If one operating rod breaks, its piston fouls, etc, the other will be able to carry its load with little if any change in cyclic rate. Additionally, the pistons and operating rod will not be attached to the barrel, so barrel changes can be made more easily. (more on that later)
• Hard Facing of the bolt face with Stellite No. 01 Alloy for increased wear resistance.
• Use of Carpenter No. 158 (AISI P6) Molding Steel for the Trigger, Sear, Disconnector, Selector Switch, (and AutoSear in full auto models), same material for the bolt, carrier, and carrier components. Additionally, these parts I've specified to be strengthened via shot peening and inspected by MPI, just like the military specifications for the M16 call for.
• Use of MIL-B-11595E instead of AISI 4140 for the barrel, like on real Mil-Spec rifles.
• Replacement of the standard charging handle with an ambidextrous non-reciprocating forward charging handle to allow for charging of the rifle without removing it from the shoulder that can double as a forward assist to help clear jams and allow the bolt to be lowered with less noise if desired.
• Chrome Plating of the Bolt Carrier and Group for increased reliability and wear resistance.
• Quick change barrel system involving an interrupted screw and foolproof 'positive lock' system similar to the FN MAG-58 "M240" with a button removal to avoid the barrel release catching or snagging with a fixed barrel extension to eliminate the need for manual headspacing, with an integrated carrying handle on the barrel that folds flat to allow for barrel changes in combat conditions without the need for an insulative heatmitt.
• Rounding of the bolt lugs and removal of the bolt face undercuts for a stronger and more reliable bolt.
• Fixed ejector to prevent the ejector from breaking and eliminate the problem of the ejector spring becoming tired due to excessive use.
• Repositioning of the buffer spring to be in line with the piston to prevent the bolt carrier group from tilting during operating cycles that plague most aftermarket AR-15 piston kits.
• Removal of the protruding recoil buffer tube to allow the use of folding stocks or bullpup configurations
• Ambidextrous controls for the magazine release, bolt catch release, both within easy reach by the index finger of either hand.
• STANAG-compatible magazines, or the use of SR-25 magazines for the H-models.
• Hardfacing of the Cam Pin Track with pressfitted Stellite No. 1 Alloy inserts to minimize wear during operating cycles and prolong receiver life.
• Hard Chroming and machine jewelling of the bolt ways to minimize wear, decrease coefficient of friction, increase reliability, and retain lubricating oils.
• Multiple position gas vent switch on the gas block, adjustible for different rates of fire or if the gas vent becomes clogged, or for use with silencers.
• Implementation of a tungsten-powder recoil buffer to minimize felt recoil while avoiding the leakage problems that plague most hydraulic recoil buffers.
• Removal of the 3-round burst system and implementation of a Safe-Semi-Full selector switch for Military/Law Enforcement/Private Security Consulting models only.
• Adjustible cheekpiece and length of comb on the stock.
• Furniture to be made of 35% Glass-filled Dupont Zytel
• Elimination of the gas key removes the need for the gas key screws to be 'staked,' which in turn eliminates the risk of the gas key breaking off or the screws fatiguing and coming apart.
• 7075-T6 Aluminium Forgings for the upper and lower, finished MIL-A-8625 Type III Hard Anodize with optional Cerakote available for other options such as Ranger Green or USSOCOM Flat Dark Earth. (This isn't really a design change, because that's Mil-Spec, but I figured I'd list it anyways just for reference.)
• Reversible upper capable of being made to eject from either side by replacing the bolt and replacement of some panelling.
• "Heavy Barrel Light Support Rifle" - "HBLSW" - models capable of transitioning from closed-bolt to open bolt configuration during semi automatic or full automatic fire (Military/Law Enforcement/Private Security Consulting models only).
• Maximum cost of $4000/unit or less.
• Monolithic STANAG-4694 compatible rail on upper reciever, and at 3 o'clock, 6 o'clock, and 9 o'clock positions on fore-end to replace the older M1913 standard yet remain backwards compatible with M1913-compatible accessories.
• Additional bolts to allow for chamberings in 5.56x45mm, 6.8mm SPC, and 6.5mm Grendel for the L models. The H model will probably be 7.62x51mm only for now.

Tell me what you think! I'm calling my creation the "D13-N0W" or just the "D13." I'd thought of other designations such as "FU-411" or "1-K1LL-U" but then realized that nobody'd take it seriously if I called it something along those lines. I'm hoping to get into the civilian and private security consulting industry, because as much as the military appeals to me, I doubt they're going to shift away from the M16/C7/M4/C8 anytime soon.

[Zixinus]

Will you make a short animation showing how the internal components work and how are they different from the standard AR-15?

[Davey]

Will you make a short animation showing how the internal components work and how are they different from the standard AR-15?

Yup! I definitely will for comparison, but that'll be a long, long way off; I've still got to finish the AR-15 first. I think what I'll try to do in that case would be to export my models into solids and use a better animation software package. I haven't done animations in NX before.

On the AR-15 I still need to finish the fire control group (ironically that's my favourite part of the AR-15...), and oddly enough I can't find drawings or non-parametric models for a carbine-length recoil buffer. I'll probably have to find one and measure it for dimensions.

[Kenny_10_Bellys]

First off I have to say I'm very impressed with your knowledge of the internal design of firearms, you clearly know what you're talking about. I'm going to play Devils advocate for the purposes of this post however, in order to give you what I hope might be useful feedback for designing this, even though I know next to nothing. Think of me as a middle manager you're trying to convince to make the gun, where I know little and you are very tech savvy.

Isn't the 'improved M4' market a bit saturated already? All the big manufacturers out there have done it; the HK-416, the SCAR and particularly the ACR/Masada. Magpul I think did the definitive job, fixing pretty much all the main problems with the M4 platform to make it lighter, user friendly, reliable and customisable. You appear to be starting with an AR-15 and are going to try and turn it into a 416, which has been done already. If your gun looks and shoots like a million others out there, what is the unique selling point of your M4 clone? Will it cost significantly less than an AR-15, or be more reliable than a 416, or shoot more powerfully and accurately than the SCAR-H, or be lighter and more customisable than the Masada?

My own feeble efforts have involved trying to design from the outside in, rather than the inside out. I made a list of desirable qualities that I wanted from a gun, then started with a clean sheet to try and get as many of them as I could into a useable platform. The biggest thing that keeps slapping me in the face is the awesome advantage of the bullpup configuration. That greatly increased barrel length is such a tempting plus point it's hard to look at designing another M4 clone. It's the way ahead, if they can iron out the niggles.

[Zixinus]

I agree I had similar thoughts, but I thought the whole point of the project is to redesign the M16/AR-15 (for fun or as a student project I'm guessing). I guess that many people don't want bullpups because its untraditional (even though the idea is almost half a century old) and because they may be more difficult to design.
I actually saw a youtube video with a guy telling that he found an error in the design that nobody is willing to talk about, but I can't find.

Anyway, yeah, I also wonder: will you look into whether you can remove the thing that makes the action protrude into the stock? That way, you can have foldable stocks. Or even allow conversion to bullpup.

[Kenny_10_Bellys]

The buffer tube at the rear of the M4 is one of the issues the M4 design has, and does indeed stop the use of folding stocks. Other famous issues are the charging handle, the controls and the recoil system.

The charging handle is mounted on the top rear, so you can't mount cheek pieces or fancy stocks on them, nor cock them easily when the gun is raised near the shoulder. The bolt release, mag release, ejector port and fire selectors are not ambidextrous, making the gun a pain for lefties or in certain stances. The gas recoil system that recocks the gun after each shot basically blasts hot, dirty exhaust straight into the bolt and that's not good for reliability. It also makes barrel changes a pain.

Magpul famously decided to try and fix the M4, and their fixes turned it into the Masada. Controls are all ambidextrous and close to hand, the charging handle is mounted forwards above the barrel and the handle can be flipped over in a few seconds to suit lefties. They redesigned the internals to lose the buffer tube allowing the fitment of folding stocks, and the recoil gas system pushes a piston far forward of the bolt group, meaning less cleaning and quick change barrels.

[Davey]

Howdy guys, sorry about the delay! It's taken me a bit of time to get back to this.

First off I have to say I'm very impressed with your knowledge of the internal design of firearms, you clearly know what you're talking about. I'm going to play Devils advocate for the purposes of this post however, in order to give you what I hope might be useful feedback for designing this, even though I know next to nothing. Think of me as a middle manager you're trying to convince to make the gun, where I know little and you are very tech savvy.

Thanks! I'll try to answer the questions as best as I can. Outside help is always appreciated, because a lot of the time when I'm so focused on one problem I forget about everything else.

Isn't the 'improved M4' market a bit saturated already? All the big manufacturers out there have done it; the HK-416, the SCAR and particularly the ACR/Masada. Magpul I think did the definitive job, fixing pretty much all the main problems with the M4 platform to make it lighter, user friendly, reliable and customisable. You appear to be starting with an AR-15 and are going to try and turn it into a 416, which has been done already. If your gun looks and shoots like a million others out there, what is the unique selling point of your M4 clone? Will it cost significantly less than an AR-15, or be more reliable than a 416, or shoot more powerfully and accurately than the SCAR-H, or be lighter and more customisable than the Masada?

The buffer tube at the rear of the M4 is one of the issues the M4 design has, and does indeed stop the use of folding stocks. Other famous issues are the charging handle, the controls and the recoil system.

The charging handle is mounted on the top rear, so you can't mount cheek pieces or fancy stocks on them, nor cock them easily when the gun is raised near the shoulder. The bolt release, mag release, ejector port and fire selectors are not ambidextrous, making the gun a pain for lefties or in certain stances. The gas recoil system that recocks the gun after each shot basically blasts hot, dirty exhaust straight into the bolt and that's not good for reliability. It also makes barrel changes a pain.

Magpul famously decided to try and fix the M4, and their fixes turned it into the Masada. Controls are all ambidextrous and close to hand, the charging handle is mounted forwards above the barrel and the handle can be flipped over in a few seconds to suit lefties. They redesigned the internals to lose the buffer tube allowing the fitment of folding stocks, and the recoil gas system pushes a piston far forward of the bolt group, meaning less cleaning and quick change barrels.

Yup, the Masada was one of my biggest sources of inspiration, along with the SCAR and Robinson XCR. All those I wanted to take a look at and see if I could design something along those lines with my own features.

Indeed the market is saturated at the moment with both ARs, AR-type rifles, and aftermarket "Improvement" AR parts, but part of the thing that I want to market this as is that it takes modularity and reliability a step even further than the competition with the no-tools, combat-changeable barrel.

The SCAR and Masada have quick-changeable barrels, but they're not what I would call 'combat swappable' - the Masada's handguards have to be removed in order for you to get at the barrel release mechanism, and the SCAR requires a pair of screws that need to be removed using an Allen key before the barrel can be slid out of the upper. Although these are infinitely faster than the AR-15, they're still not what I would consider combat changeable. The same goes with the Robinson XCR, some other parts need to be removed first if you want to change the barrel. I think the piston guide needs to be taken off first.

One criticism I have of the Masada is that the operating rod and piston are both also a part of the barrel and will come with it when the barrel is taken out. With an interrupted screw and locking lug similar to the system seen on the FN-MAG, as well as a free-floating operating rod, this eliminates the problem of having to remove the handguards (no handguards would mean no bipod, and no bipod means there would be nothing to rest the gun on when changing an overheated barrel) and more importantly makes it nearly impossible to fuck up the barrel change - unlike the AR-15 which would be torqued in, this system would be a 'go-no-go' system. Either the barrel clicks into place and locks to be combat effective, or it doesn't, plain and simple, unlike the AR-15 or SCAR's system of threaded fasteners that can be torqued improperly or insufficiently, and is an improvement on the Masada's system that requires partial disassembly of the upper in order to be made effective. Add that to the idea of using an insulated carrying handle on the barrel itself to eliminate the need for a heatmitt, and you have yourself a contingency plan in case the barrel should overheat.

Add that to a fixed ejector to eliminate the problem of the M4/SR-16's problem with the little ejector spring failing in the heat, and with dual pistons, and that should confer some serious, heavy-duty reliability, especially in desert or aquatic environments. As a consequence, the rifle itself will most likely be a little bit heftier than the Masada, SCAR or the 416 because it will be slightly beefier, but it should be just as modularized, and have even fewer points of failure, and a redundancy in the gas system that will allow it to function even if one piston or one operating rod completely fouls, jams, or breaks. And if it does, the idea would be for me to limp along on the single remaining piston until I get the opportunity to hit the barrel release button, twist the barrel's carrying handle so it falls out, drop a new one in place, and resume firing, just like a machine gun, no need to remove the handguards, no asbestos heat mitt to have to carry, no tools or screws to lose or fumble, and no armourer's wrench to have to purchase and carry separately.

One issue I don't particularly like about the H&K 416 and all other aftermarket piston systems is the buffer. As mentioned before I wanted to get rid of the recoil buffer on the AR-15, so I could turn it into a bullpup with a simple trigger linkage and a stock accessory, but the reason for my dislike of the 416 is a bit different than that; the AR-15 was originally designed to buffer a straight-line impingement system. The piston action of the 416, as well as a number of other aftermarket piston systems places the force acting on the bolt carrier above the bolt carrier group, for which the buffer was never designed to accomodate. This causes premature wear and tear on the inside of the recoil buffer tube and the recoil buffer detent pin, and can even start wearing away the insides of the upper prematurely.

I agree I had similar thoughts, but I thought the whole point of the project is to redesign the M16/AR-15 (for fun or as a student project I'm guessing). I guess that many people don't want bullpups because its untraditional (even though the idea is almost half a century old) and because they may be more difficult to design.
I actually saw a youtube video with a guy telling that he found an error in the design that nobody is willing to talk about, but I can't find.

Yeah, at the moment it's a student project, although I dropped interchangeability with standard AR-15 parts a while back. It's likely I'll still use the fire control group because I like the AR-15's fire control group, but I think that at this point it's easier for me to design a new gun around the AR-15 parts that I like than try to maintain some kind of reverse-compatibility with existing AR-15 designs. I would love to sell it to civilian, private military and private security, law enforcement and military interests if I could ever get the ball rolling though. But at the moment, it's just me on my own, and whatever I can bring in.

Anyway, yeah, I also wonder: will you look into whether you can remove the thing that makes the action protrude into the stock? That way, you can have foldable stocks. Or even allow conversion to bullpup.

Yup, the Bullpup idea I've already discussed up here:

• Replacement of the standard charging handle with an ambidextrous non-reciprocating forward charging handle to allow for charging of the rifle without removing it from the shoulder that can double as a forward assist to help clear jams and allow the bolt to be lowered with less noise if desired.
• Removal of the protruding recoil buffer tube to allow the use of folding stocks or bullpup configurations
• Reversible upper capable of being made to eject from either side by replacing the bolt and replacement of some panelling.

Part of the reason why the bolt is made like that is to trip the autosear, in fully automatic or burst-fire configurations. If you take an M16 apart and look at the bolt carrier, you will notice that the lower half of the bolt carrier protrudes as much as the top half. This is done so that when the bolt slides forward and locks up, it trips the G.I autosear, which holds the hammer. In full auto mode, the selector switch will trip the disconnector and cause the disconnector to lift up and let go of the hammer. I intend to amend this and reposition the buffer spring to be collinear with the axis formed by the plane between the pistons. This is to prevent the bolt carrier from tilting and it eliminates a lot of the tilt issues experienced on the other aftermarket kits.

To make the bullpup ambidextrous, I've been toying with a forward ejection system instead of a reversible one, like on the FN2000/FNS2000 rifles. A forward ejection system would solve the issue I have about the cases being ejected into the user's face, but it would add a bit more complexity to the system overall, which I'm trying to cut back on. While I dislike bullpups out of principle because of the problems with the trigger linkages, I recognize that the ability to have the same effectiveness and barrel length in a much shorter, more compact and ergonomic package is also something that could be very important.

[Davey]

--- Oops, double tap.

[Kenny_10_Bellys]

The bullpup layout confers so much of an advantage that I think it outweighs the issue of sloppy trigger linkages. That additional accuracy, power and compact planform are everything you could want from a rifle design. Currently I only own Airsoft rifles (they took everyones guns away in the UK nearly 20 years ago after the Dunblane killings) but even in using them you can see it. I have a couple of M4 variants, and they're nice and familiar to use and shoot just fine. Now I also have a license built IWI Tavor which is my main gun, and while as short as my CQB M4 it has a barrel as long as a full length M16 with all the advantages that confers.

Having said that, I've owned or used Tavors, SA-80 variants, FAMAS, and Augs both real steel and Airsoft, and to some extent every one of them suffered from issues with the trigger linkages and fire selector. As curses go it's not as bad as some, but it does marr the user experience and piss you off when you least need the hassle. I can only think that there is a relatively easy solution out there somewhere, it's such a trifling thing to spoil a superb engineering idea.

The forward ejection on the FN2000 never really looked like a good idea to me, it looks like a jam waiting to happen. I'd be looking to get rid of the old brass downwards like the P90 or forwards without the use of a tunnel.

[Zixinus]

I recall that the Koborov TKB-022 solved the ejection problem by the shaping of the ejection slot: it's formed to make the falling out cases forward. I may be mistaken.

[[R_H]]

What program did you use to make the models?

[Davey]

The forward ejection on the FN2000 never really looked like a good idea to me, it looks like a jam waiting to happen. I'd be looking to get rid of the old brass downwards like the P90 or forwards without the use of a tunnel.

Ejecting straight down would be great, although I'm hoping to use STANAG magazines, so I'm at a bit of a loss to how I could get it to do that at the moment. Switchable ejection is something that I think I could do, although it's not the greatest of ideas because the ability to switch hands immediately for places like built up areas would be a pretty nifty feature.

One thing I should mention is that bullpup stocks themselves are illegal in Canada, but bullpup rifles aren't. Guns that are assembled from day one as traditional layouts can't be converted to bullpups, but interestingly enough, guns that are assembled as bullpups from the start (FNS2000, PS90, or in other words the civilian versions of the FN2000 and P90) can be made non-restricted if their barrels are long enough.

I recall that the Koborov TKB-022 solved the ejection problem by the shaping of the ejection slot: it's formed to make the falling out cases forward. I may be mistaken.

Ooh. That's an idea, although I wouldn't want to try to interfere too much with the path of the ejected casing. They can come out pretty hard, with fixed ejectors. Still, a good case deflector could be a face-saver...

What program did you use to make the models?

Siemens PLM NX 7.0. Since the school uses it and it's got pretty good parametric modelling I figure it's a shame not to use it, even if it can be an incredibly buggy and finicky at times. It does the job pretty well.

[[R_H]]

That's why I recognised it, we use it as well. Fun times, did you have any trouble using touch - infer centre?

[Zixinus]

Oh, and I forgot to mention: this is pretty damn cool.

Tell me, have you ever looked at pistols too?

Switchable ejection is something that I think I could do, although it's not the greatest of ideas because the ability to switch hands immediately for places like built up areas would be a pretty nifty feature.

From what I heard, you should put that down on the priority list: only people like special forces and elite units actually bother with that stuff. Most soldiers fire from the position they are used to.

[Kenny_10_Bellys]

Changing from one shoulder to the other to fire around obstacles may be more common than you think. Lots of training videos cover it, and even airsofters study them for the proper techniques and they have no brass to eject. I haven't seen it get in anyones way yet, unless the brass hits something on the way out and bounces back. With a bullpup style rifle it will cause issues though, where you might well be sticking your face next to an ejection port if you swap shoulders in a firefight. Again it makes a great case for getting rid of the brass some other way, either forwards or down. The FN2000 has that interesting tunnel system moving the spent cases forwards until they start falling out after 3 shots or so, but I worry about the reliability of that.

[Norade]

Changing from one shoulder to the other to fire around obstacles may be more common than you think. Lots of training videos cover it, and even airsofters study them for the proper techniques and they have no brass to eject. I haven't seen it get in anyones way yet, unless the brass hits something on the way out and bounces back. With a bullpup style rifle it will cause issues though, where you might well be sticking your face next to an ejection port if you swap shoulders in a firefight. Again it makes a great case for getting rid of the brass some other way, either forwards or down. The FN2000 has that interesting tunnel system moving the spent cases forwards until they start falling out after 3 shots or so, but I worry about the reliability of that.

I don't know guns all that well, but what if a little gas was vented into an FN2000 style system to help move casings through faster. A manual clearing lever could fold down flush and appear when flipped up so that little groves would catch shells and force them out. I'm sure people that know more can think of ways to improve these ideas.

[Marko Dash]

i know the main purpose of a bullpup is to reduce the weapons OA length, but is there anything that uses this configuration while having the same length as a conventional layout by way of having an even longer barrel?

[Davey]

That's why I recognised it, we use it as well. Fun times, did you have any trouble using touch - infer centre?

Hee hee, awesome.

The 'snap to' selection thing for the centre? Usually I haven't experienced any problems with that. The features usually work the way they're supposed to, well, most of the time, it's just that sometimes I run into those "Internal Error: Memory Access Violation" errors that pop up randomly and then the program either crashes or I have to stop it and restart it otherwise it'll corrupt the part on save. I started back on NX 4.0 for SunOS, and it's gotten a lot more reliable since, but it still does that from time to time.

Oh, and I forgot to mention: this is pretty damn cool.

Tell me, have you ever looked at pistols too?

Thanks! Yup, I love all sorts of guns, so I'm working on a couple at the moment, in fact.

If you want to see pistols, I'm actually doing a Beretta 92FS right now at the moment. The model itself is not mine, I got a .igs solid from CNCguns.com and I intend to try to make my own version, using his example as guidance.

I added some text at the front that I'd like to engrave later on, once everything's been anodized. I added some text to it for the lulz and also because a Beretta 92FS was seen in that movie.

Also on the books is a 1911 - I simply could not afford not to do one! But I haven't got any models for that just yet.


And here's what the output of the NC program looks like so far in NXCAM. I've got a lot to go. Machining something this complex has to be done fairly carefully, and done in multiple setups, because it's got a ton of undercuts and very tight and small areas. I haven't been at it for very long as you can tell, just doing the outlines. In the CAM simulation you see in this picture here, I'm going to be doing is starting with a solid piece of 7075-T6 aluminum alloy flat bar and machining it down bit by bit.

And if it interests you, I'm doing an M60 Semiautomatic SLR completely from some old blueprints I found on the web, no reference solids or solid models:
Bear in mind that this is also a work in progress, the rails are done but the trunnion isn't.

It took me a while to see how the rails fit together but when I did I laughed out loud, because it's a pretty cool system - the rails are the parts that actually take the force of the bolt slamming back and forth, not the receiver channel itself. I'm specifying MIL-S-16974 (AISI 8640) for the rails and trunnion instead of 4140 Alloy, and thickening the metal on the receiver channel slightly to solve the issue of the receiver stretching at extremely high round counts. After the receiver's been made I'm gonna have to complete it using a semiautomatic part kit and have it registered as a non-restricted self-loading rifle. Because post-WWII belts are banned here in Canada (or limited to a five-round capacity) I will have to tweak the feeding pawl to accept non-disintegrating metal link belts instead of the typical disintegrating ones the M60 used if I want to keep it as a non-restricted SLR.

I would love to do an FN MAG-58 or a PKM machine gun, because the MAG is supposed to be way more dependable and way more reliable, but unfortunately I haven't got prints for those.

From what I heard, you should put that down on the priority list: only people like special forces and elite units actually bother with that stuff. Most soldiers fire from the position they are used to.

Changing from one shoulder to the other to fire around obstacles may be more common than you think.

Yeah... I'll see what I can do with that. I got that thinker of mine going.

I don't know guns all that well, but what if a little gas was vented into an FN2000 style system to help move casings through faster. A manual clearing lever could fold down flush and appear when flipped up so that little groves would catch shells and force them out. I'm sure people that know more can think of ways to improve these ideas.

Well, I'm trying to actually prevent that, in fact. The less gas that leaks back into the gun, the better. Twin pistons is already a pretty complicated system and don't want to have to worry about a third, when I've got a fixed ejector.

i know the main purpose of a bullpup is to reduce the weapons OA length, but is there anything that uses this configuration while having the same length as a conventional layout by way of having an even longer barrel?

Yeah, the Steyr AUG HBAR-T DMR is like that, I think.

[Norade]

I don't know guns all that well, but what if a little gas was vented into an FN2000 style system to help move casings through faster. A manual clearing lever could fold down flush and appear when flipped up so that little groves would catch shells and force them out. I'm sure people that know more can think of ways to improve these ideas.

Well, I'm trying to actually prevent that, in fact. The less gas that leaks back into the gun, the better. Twin pistons is already a pretty complicated system and don't want to have to worry about a third, when I've got a fixed ejector.

Would some sort of flip up clearing handle work then? Say a piece of the ejection tube can flip up on edge and be pulled forward along a groove to manually clear any stuck casings. Most of the time they would self clear exactly like the FN2000, but jams are now a quick fix.

[Davey]

Would some sort of flip up clearing handle work then? Say a piece of the ejection tube can flip up on edge and be pulled forward along a groove to manually clear any stuck casings. Most of the time they would self clear exactly like the FN2000, but jams are now a quick fix.

I really don't understand what you're trying to get at. The charging lever and the forward assist are used primarily to clear a jam. Any additional systems would simply be redundant.

[Norade]

Would some sort of flip up clearing handle work then? Say a piece of the ejection tube can flip up on edge and be pulled forward along a groove to manually clear any stuck casings. Most of the time they would self clear exactly like the FN2000, but jams are now a quick fix.

I really don't understand what you're trying to get at. The charging lever and the forward assist are used primarily to clear a jam. Any additional systems would simply be redundant.

This isn't a jam of the feed, but a jam of the ejection tube on the FN2000 which I'm unsure if the charging handle clears. Above a poster expressed concern over that system jamming if a spent casing were to stick so I figured a manual lever that can clear such a jam quickly would solve that issue.

[Kenny_10_Bellys]

The FN2000 gets rid of its shells along the top of the gun and then out the front just above the muzzle. I believe there is actually a flip-up section at the back end of the top rail which gives access to the ejection system, allowing you can clear stuff manually should it lock up. It's a novel way to get rid of brass away from the operator, I just pointed out that it has the downside of adding a new point of failure to the gun compared to just flinging it out the side.

As for full length bullpups, look to the sniper rifles! Barret make good use of the layout to give immensely long barrels on their immensely powerful guns, like the M95 and M99 models. Others like the famous WA2000 use the bullpup layout to make for very handy yet accurate sniper platforms. The handle on the WA is very small though, like its built for children, and then again I've hauled a Barrett around a forest and it's like carrying a length of railway line.