Only time my Issue M16A2 ever failed was when shooting "New" ammo at the range for qualifying. The ammo was loaded over pressure and was bulging and rupturing primers. It was also locking the bolt back pretty violently. There were several of us who had issues with the ammo and we had to gather up all the ammo and turn it in. They gave us a new lot of ammo and after the armor looked over our rifles we were allowed to requalify.