No formula for me. I went to my buddies place to pick him up to go to a match. He was finishing up loading ammo for the match on his 650 w/ a Mr Bullet Feeder. I watched him load 100 rounds in 4 minutes while we were talking smack about who was going to kick who's butt at the match. At the time I had a 550 it took me about 15min to load 100rds on the 550. The Monday after the match I went down to the local Dillon dealer and picked up a 650 and a Mr Bullet Feeder, been happy ever since.