As to M16s, the government went to a cheaper, dirtier powder, than what was recommended by Eugene Stoner. This too was a major cause of jamming.
As to revolvers, I've had two types of issues that have jammed cylinders which would have caused a shooter to die in a firefight. Both of these issues happened on S&Ws.
The first which I've seen happen many times on the range is when unburnt powder gets under the extractor star. The thickness of the powder granule caused the star to not seat flush but still allowed the cylinder to close. But because the star was pushing out on the frame, it locked the cylinder and not allow it to rotate. The cylinder had to be forced back out, cylinder unloaded, then the extractor had to be held out while a rag wiped away the powder that was under it.
The second type I ran across only once. A female cop came in (to the range) to requalify and her cylinder was frozen in place. It was so bad, I took her off the firing line and had to work on her revolver for about 15 minutes. Her ammo had expanded so bad, again pushing against the back of the frame, that the pistol was unable to function (this was her duty gun). Then the rounds had to be hammered out of the cylinder. Now this happened in South Houston where the temperature can get over 100 degrees outside, 90% humidity, come into an air conditioned car or building where it is 65 degrees, and do this repeatedly throughout the day, day after day. She probably had not touched her revolver since her last requal, and luckily hadn't needed to draw it.