Look I carried and fired the M16 in the army. It is a great garage queen... Keep it clean and unfired it was fine. But it gets really really hot after a 3-4 mags of high rate firing. The bolt gets carboned up as it is blowing powder hot powder residue onto the bolt. Really hot, and really dirty and the lube is burned up. It jams. The new Ruger piston driven SR 556 has four potions on the gas impingement system that lets you select how much gas is used to move the piston. So you can adjust for bad ammo or a dirty weapon and keep firing. Seems like a great idea but needs to be tested. So I was never a big fan, and lots of controversy on the gun forums surrounding the issue of gas impingement vs piston.
Enjoyt the Rugar, you couldn’t give me one. THE rod is pinned inthe system, it cannot be removed for cleaning.
I have an AK in 223 - after a couple of mage it is too hot to hold - the power burns so hot. My SKS (762x39) can be fied all day and is not all that hot.
Problem? Not an engineer, but the ammo and auto fire had to be part of it.
The M4 is also much more accurate - a lot of the troops are now using scoped weapons these days.