Had the chence to test the upper today. Started out with 250 rounds of Federal champion 36gr. plated on full auto to break it in.
After that here are the targets with open sights at 25 yds.
Federal 36gr. plated HP
American Eagle plated 38gr. HP
PMC Sidewinder 40gr. Solid
All the targets were done with open sights at 25yds. Upper was taken out of the box and fired. No lube was added at any time. Targets were 1 box of ammo of each brand tested. The PMC was the only one that had a few rounds that had failure to fire (5)rds. out of 50. the rounds were loaded again and did fire on the second strike.
Full auto was with Federal 36gr plated and was very reliable...And FUN...