I've never seen one fail. I am unfamiliar with the term .308 gasser. The 7.62 NATO weapons we issue (M240s, M110s,MK48s) generally get purpose specific optics like an M145 MGO (Machine Gun Optic, ELCAN/ACOG) or a variable power scope. I've seen M68s on M-249s 5.56mm SAWs without issue. You just need to make sure you hear three clicks and inspect the optic to make sure nothing comes lose.
I'm sure some of our other LF brothers can probably give you come better info.