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.