Further on the M16 and the powder change

I'm doing this as a separate post instead of adding it to the other.

In comments I got
IIRC, the original powder specified for the M-16 was an "IMR" (stick) type. A ball powder was substituted for some reason. The problem was that as long as the ballistics requirements were met, the specification for the powder didn't put any limit on the content of calcium carbonate. (Calcium carbonate is used as an antiacid.) As a result, the maker used a lot of the stuff. This resulted in a calcium based fouling in the gas system which was extremely hard to remove. This and the early report that the M-16 never needed cleaning had predictable results.

I did some checking(hey, I was in a hurry last night) and this does indeed cover it. I also found this:
1965 - 1967. Field reports from Vietnam began to look much more pessimistic. M16 rifles, issued to US troops in the Vietnam, severely jammed in combat, resulting in numerous casualties. There were some causes for malfunction. First of all, during the introduction of the new rifle and its ammunition into the service, US Army replaced originally specified Dupont IMR powder with standard ball powder, used in 7.62x51mm NATO ammunition. The ball powder produced much more fouling, that quickly jammed the actions of the M16 unless the gun was cleared well and often. This pitifully combined with the fact that the initial M16 rifles were promoted by the Colt as "low maintenance", so, for the sake of economy, no cleaning supplies were procured for new M16 rifles, and no weapon care training was conducted fro the troops. As a result, soldiers did not knew how to clean their rifles, and had no provisions for cleaning, and thing soon turned bad. To add the trouble, the ball powders also had a different pressure curve, so they produced higher pressures at the gas port, giving the rise to the rate of fire, and, thus, decreasing accuracy and increasing parts wear.

I remember reading, years ago, accounts of units where the only people who had any real understanding of cleaning the thing were those who'd been shooting before entering the Army; and they had to rig pull-throughs and such to do it.