I just built a rifle for 3-gun and shot it today. It has JP LMOS carrier, buffer, spring, and a Geissele s3g. I sighted in a Tac30 and chrono'd some new loads at 25 yds and it ran flawlessly for 80rds (5 rds at a time). I took it to the 50yd line to sight in and immediately did a 3 shot "bump fire." I didn't change anything from the 25yd line. Same trigger pull (slooooooow), same cheek weld, etc.
I couldn't figure it out. When loading one round at a time, the bolt caught on the empty mag. When loading one at a time without mag, the hammer would follow after the shot and would probably cause a bump fire. Not sure why it would not act out for 80rds but then all of a sudden just start bumping. Anything i can do to stop this? Maybe pull the trigger harder?