We've been out training for 2 weeks we're on our third week. We've noticed that some of our m4s have been having issues. Cleaning our M4s we noticed that gas rings are missing from the bolts of the M4s that are having issues. These are brand new M4A1s made by FN. We had beat up Colt M4s before that never had this problem. We're scratching our heads as to whats happening. We did some shooting but it was nothing serious.