Colt SP1- Sheered the bolt carrier nearly in half length-wise, busted the extractor in half and IIRC, blew the ejector out as well as breaking the bolt catch...And dumped ~15 rounds out the bottom of what used to be a 20rd Colt mag. All w/ one shot. ARs are not meant to send 110 grains down range.
Sorry no pics but this was back in 1998 or early 99.
I was shooting through an impromptu course my Dad and I had set up when the rifle failed to fire. I charged the weapon again and heard a distinct "CLICK". I put the weapon on the deck and continued through the course w/ my sidearm. My father, who was on a hill observing me, went down and picked up the Colt taking it back to the truck. As I finished the course and returned to the top of the hill, I saw my Dad at our target range and he charged the weapon and looked at what appeared to be a spent case that was ejected. He figured I just had an undercharged round which failed to cycle the action. Somehow, he had the good sense to hold the rifle low by his hip and away from his body when he pulled the trigger. He thus found out that the "undercharged" round, his own reload in his own rifle BTW, was actually a squib load w/ no powder. The "click" I heard was just the primer sending the bullet up the bore a few inches or so. He then charged a round behind the bullet in the bore and KABOOM. Scratch one Colt SP1 upper. The lower was fine aside from the broken bolt release.
The only other things I've seen worn or broken was a set of gas rings, an extractor. (Which was a SOB to troubleshoot) and a BM plastic trigger guard that broke when the rifle was mounted on an ATV gun rack resting on the guard.
Sly