Yet another first- a sheared bolt lug on a civilian AR that has never seen full auto fire. I saw this from time to time in the army on M4A1 carbines, almost overwhelmingly on those that had seen excess full auto during range "shenanigans" (because there is little application for such activity, and even less application for it to be done in any significant amount). This is from a gun I built for training/range use about 18 years ago. No idea how many rounds have been through it, but I have shot out 3 barrels so far. I have noticed that things are breaking more often on it as of late- 2 weeks ago, it wouldn't eject. When I removed the ejector spring, it came out in 9 pieces. I have also broke various pins, trigger group components, gas rings, a buffer, and so on.