[Slamfire]

I would suspect an out of tolerance condition in case/chamber dimensions, or a really hot round.

Breech friction is in fact bad for semi automatic mechanisms. If the bolt cannot pull the case out, the gun will jam. If the case is an mechanical interference fit in the chamber before firing, after firing it will be wedged in the chamber even more. If the case is hard stuck in the chamber, a semiautomatic mechanism will then rip the rim off, or break its extractor.

Another issue, one that got a lot of GI's killed in Vietnam, is high port pressures. This was due to using powders with inappropriate pressure curves in the weapon.

If the pressure curve at unlock is too high, the case is stuck to the chamber walls, and the semiautomatic mechanism will rip the rim off or break its extractor.

So, if the round was hot, or was using powder that gave an inappropriate pressure curve, then that could be the problem.

The AR15 was not designed with steel cases in mind and the extra friction between steel and the chamber could be the issue, but I am more inclinced to think you had a hot round.