Never happened to me either and only saw it when the gas system was fouled (because of poor cleaning by the user).
The M60 on the other hand had it's issues, right up until we had a decent armourer from another unit look at them. Our battalion armourer had been recycling old worn out parts for years and almost every last gun in the battalion was unservicable!
One private in my plattoon was put on on a charge for a UD - unauthorised discharge. The weapon was so worn out that the safety sear slipped and roughly 50 rounds fired before it could be stopped by breaking the link (belt).
Six months later after he'd served his punishment the problem was found and the weapon repaired by somebody actually compentant...
