There is an interesting discussion on 10-8 about bolt's breaking. Kevin Lamb stated that he sees 6-8 mil-spec bolts (most likely Colt bolts) break out of every 40! He doesn't say, but am guessing that that the weapons used are MK18 and M4's (which as we know, have carbine length gas systems).
I then get a PM from a Battalion Armorer stating that for almost 10 years, he has only come across one broken bolt.
The interesting part is that they are running A2/A4's. This points directly to what we have always known, that the carbine gas system is MUCH more violent and hard on components than the rifle length gas system.
C4