Way i heard it was that commercial ammo did't jam but using up our stockpile of dirtier WW2 powder overwhelmed the gas system..(?)
Of course the solution was 'troops should clean their weapons more often'.
There have been learned books written on the subject. WW2 powder had nothing to do with it, they switched to a different cheaper powder and changed the muzzle velocity. The WW2-era smallarms powder was all gone by the end of Korea.
The commercial ammo stayed with the original powder spec and didn't have a problem. The issue ammo had issues with the twist rate which caused greater fouling.
And yes, the "solution" is still the same. Even though the problem now is the sand and crud that the weapons operate in....
All you guys are off a bit...the "Generals" who took the original rifle for testing didn't like the cyclic rate which was a bit slower than what they wanted, plus they liked doing business with their old buddies who manufactured the powder they liked, so they changed the powder to up the rate of fire and used a specific powder that jammed the works.
The original AR-15 used by the early Special Forces working as advisors worked like a charm and was as effective as the AK-47 in adverse conditions.
The jamming was fixed by chrome plating and the handle was installed because some nit wit General wanted one. They didn't want to admit that they had screwed up a beautifully designed and effective weapon.
I, um, did a little work years ago on these toys.