had one fail and all that happens is a misfeed, the last poster is correct no out of battery but bolt does not have time to lock there for it tries to act like a blow back design instead of its intended gas operation and well the bolt and carrier are to light for this so it will cycleway to fast and usly jam or close on an empty chamber, when mine did it the most that would happen is bag-jam only once did i get a double tap and thats what made me find the problem. the sear would catch when i cycled it by hand but the sear spring was to weak and when it cycled on its own it some how would not catch, so no its not that ez to do "you know what" you surly need the right sear and a rate reducer to even come close which is how the "real" one works