Would have to see it while being fired. Does cyl lock up tight on cocking? Caps will make a mess on back of cyl, normally. I would think if nipple was bad it would blow hammer back, have seen that happen on an old shotgun with wide open nipple. Make sure right nipples are installed, right charge is used, and cyl locks up tight(no rotating by hand) when pistol is cocked. If not sure, take it to a gunsmith before your friend has an injury.