Oleg has a good piece on how the free market affects the development of rifles:
Logistically, the G36 and its now-discontinued civilian variant SL8 are dependent on HK for service and parts. Unlike the AR15 and the AKM derivatives, these rifles do not enjoy wide aftermarket support. The same is even more true of the P90, of which no civilian version even exists. The availability of parts and of armorer expertise strongly favors the established designs produced by several manufacturers.
The situation is a result of two factors. The first is the obstacles placed by the US laws on the way of any company wishing to make or import modern small arms for civilian use. The severity of that problem varies over time but adds restrictions and uncertainty to any business plans. The second is the reluctance of some companies, notably H&K, to even consider the civilian market as important. In the US, that civilian market is large, diverse and, in effect, an extended beta test of any new or improved weapon system. Not selling to individuals cuts off an important source of feedback on the ergonomics and reliability. Gaming software companies understand that and market variants of the army training simulators to the public at large.
There’s a great deal more and you should read, particularly the various safety and reliability problems with the FN P90 and the H&K G36. Notably that the 5.7 round is only as effective as a 22 magnum. And, also, FN recently started selling the FN P90 in a civilian version, though various sources report that the wait time to get one is over one year. That said, this is precisely why I do not buy any H&K products. Not even their high reliability AR magazines or hats. They’ve essentially told us gun loving civilians that they will not cater to us, unless we want a USP or a sporterized rifle, like the SL-8. I’m a rifle sort of guy and I like them to look and function a certain way. The more they look like they’d give Diane Feinstein a conniption, the more I want one. If they made a G36 and an XM-8 in a civilian configuration, I’d buy one of each. With H&K’s financial issues, maybe they’ll reconsider and focus a bit on us civilians.
The other issue that the lack of a market creates is there will be no new rifle for the military developed in the US. US gun makers (except for Colt) rely heavily on the civilian market. No one is going to develop the next assault rifle unless they can immediately make money off of it and US military contracts are way off in the future. Sure, there’s the occasional smaller company that caters to them but they seem to do so more from a hobbyist standpoint than a business standpoint.
Regarding the AR-15, the facts are it is the longest serving rifle in US military history. Lasted longer than the Garand and the M1A. The reason is it’s a damn fine rifle. It has some problems but they can be fixed. Those problems are the dirty gas system (it eats where it shits) and the less than effective round that the military uses. There are already fixes for those, such as a switch to the 6.8SPC or the 6.5 Grendel rounds and switching the gas tube system with a gas piston system. And these fixes came from the market. Billy Bob tinkering in his garage probably came up with the first piston system and a hobbyist created the 6.5 Grendel. Also, the fact is that the XM-8 only fixed one of those problems because it fires the same 5.56 round the AR-15 does.
Addressing the market’s impact on guns, Marko writes:
. . . there’s only so much you can do to a HK91 or a G36, despite the Lego-like nature of the latter. The problem is that it’s the wrong kind of Lego…H&K intended the G36 to be modular so it could be switched from a rifle to a carbine to a light machine gun in a hurry, but it’s modular only in that it can be reconfigured to meet military mission needs without having to invest in three different weapon systems. It’s Armorer/Supplier Lego, which looks great on paper.
The AR, on the other hand, can be turned into a varminter, a match rifle, a rimfire plinker, a pistol caliber carbine, a service rifle, a commando carbine, a large-bore specialty gun and a capable sniper rifle just by pushing out a few pins and swapping out a few user-changeable parts. That’s true modularity, and because of it the AR is far more flexible than any other centerfire rifle. It’s User Lego, fun in a box, do-what-you-want, and 90% of the AR uppers on the market simply wouldn’t be available if the only AR customers were government armorers. No wonder the design keeps trucking despite its length in service.
I’m going to have to disagree a bit and state that the reason the AR and 1911 are modular is because they’ve both been around for decades. And the market made the modifications. The AR did not start out modular and only really became so in the 1980s with the development and wide use of the M4 carbine. Not sure when the 1911 got all gun geek on us. If the G36 were available to civilians, was on the market for a while, and had a wide customer base, it would become modular because folks would make adjustments to it. The market is why you can get free floating barrels, modular rail systems, stocks with better cheek-welds and just about any caliber you could want for AR carbines. Not because the military asked for them. The same would happen for the G36, if it had a market.
I expressed sadness before that if the military adopted the XM-8 that it would be the first time in US history that the military’s main battle rifle would not be available to citizens (and for you purists, it’s actually the second as the M4 carbine was not released prior to 1986 but some civilians converted their NFA registered M-16s to M-4s). And I think it’s safe to say that without citizens, the US military wouldn’t have its current battle rifle.