The bolts on my CMMG bolt carrier were loose! I was afraid I was going to have to tear down 400+ reloads!
I'm guessing that either it had a poor staking job or it wasn't properly torqued. Or both. I tightened it back down with some blue Loctite (all I had at the range), whacked it with a punch and pounded 145 rounds through it. No problems after that.
I also got to shoot a .458 SOCOM. Bad ass. I don't think I want one, I'd rather get a .45-70 guide gun. But it was pretty sweet. I probably won't turn one down if the price is right.