Refining the rifle

It probably doesn't get more basic than this. The M16 rifle has been around since the 1960s. Age aside, the rifle has several critical problems, namely stopping power and jamming. 2 new rifles attempt to resolve each issue. The Barrett M468 introduces a 6.8mm cartridge that provides more stopping power as compared to the 5.56mm cartridge. The Heckler & Koch HK416 uses a gas piston system that does not introduce propellant gases and the associated carbon fouling back into the weapon's interior. This was a problem with the M16, which caused jamming of rounds, which could only be prevented by frequent cleaning. Both weapons are available as upper receivers, meaning to say that existing M16 lower receivers can be reused, resulting in savings in costs and also training times. Not that the US Army seems to be interested though, as the front runner in contention for the M16 replacement is Heckler & Koch's XM8, which is a modified G36. The XM8 uses 5.56mm ammunition, and is an offshoot of the failed OICW project. But all 3 are conventional layout, as compared to a bull-pup design, with the magazine behind the pistol grip. A conventional design is better for urban warfare, as the rifle would be capable of being fired with either hand. While they're at it, a bullet-trap grenade should also be introduced, together with an in-built battery-free reflex sight. What about the millions of 5.56mm rounds lying around in most countries's armoury? Simple. Most countries deploy a squad automatic weapon [SAW] of sorts, e.g. M249 & Ultimax 100. These utilize 5.56mm rounds, so they can continue to utilize the surplus ammunition. Also, recruits could hone their shooting skills [and cleaning skills] on the original M16. True, the logistics of providing 3 calibers [5.56mm, 6.8mm, 7.62mm] as compared to 2 will be tougher, but that should not stop the introduction of a better cartridge that will kill the enemy with 1 shot, instead of the 2 or 3 that the M16 needs. [even a room clearing section of a field manual recommends a "double tap", 2 rounds fired in quick succession] While we're talking about rifles, it might be interesting to consider that the US Marines are sticking to the M16A4, the Special Forces have bought the FN SCAR, and the Army still hasn't decided. It wouldn't be strange if they had different calibres, but they all stick to 5.56mm. Could it be politiking that's preventing a change for the good?