[escherplex]

In discussions with older Viet Nam vets there were numerous complaints about the reliability of the earlier M16s. Seems squads would use captured AK47s when they could since they were found to be considerably more reliable in combat scenarios. Always seemed strange that the military wouldn't have adopted some re-engineered Kalashnikov design. The vets chalked that up to bureaucratic chauvinism.

[int_19h]

AK had its own issues, especially with accurate full auto fire. Adoption of M16, on the other hand, was partially backed by Project SALVO concept of accurate burst being much deadlier than a single heavier round. Originally it was supposed to be about flechettes, but they couldn't make that work. On the other hand, AR-10 was already there with a design that made recoil mitigation a priority - straight stock in line with bore, lighter reciprocating parts, and recoil impulse directed along the bore axis with no lateral component like you get from a piston. So scaling it down to a smaller round made sense.

And the design is not inherently less reliable - depending on the conditions, it can actually outpace AK. AK is more reliable in a sense that it can tolerate more obstructions in the action before it jams; but at the same time, loose tolerances and the design of its safety make it that much easier to get dirt in. So if you dump a lot of mud on both, AK fails first, even when you pit it against the original Vietnam-era M16 design - take a look:

https://www.youtube.com/watch?v=DX73uXs3xGU

https://www.youtube.com/watch?v=YAneTFiz5WU

https://www.youtube.com/watch?v=LyXndCxn9K4

[mgarfias]

well, Stoner did design the AR-18/180 in ‘63 after the AR15 had been sold to colt and adopted as the M-16.

[magila]

I'm not sure what you're getting at. The AR-18 was intended as a cost-reduced substitute for the AR-15, hence the change to a stamped steel receiver instead of forged aluminum. Design wise the AR-18 is still more closely related to the AR-15 than the AK-47, although it is significantly different from both.

[darkpuma]

The AR-18 was in fact a technically inferior design. In an AR-15/M-16, the big deal with the "direct impingement"[0] system is that all the reciprocating mass is in line with the bore axis, which avoids imparting any angular moment into the rifle making it easier to keep on target when shooting rapidly. The AR-18 throws that away by having reciprocating mass (the short-stroke piston) above the barrel.

And "shits were it eats" jokes aside, the 'DI' system of the AR-15/M-16 is very reliable. If you look at close in high speed footage of AR's and AKs being fired, you'll see that both rifle designs vent a lot of combustion gasses into the receiver when the cartridge is ejected, so the cleanliness of an AK compared to an AR is somewhat exaggerated.

[0] Which is in fact a piston, with the 'piston' being the rear of the bolt, and the bolt carrier forming the cylinder; driven apart when the hot combustion gasses are piped in between them. But this is a controversial nitpick.