"How quickly can an auto-dispenser meter 50 grains of powder?"
I use a RCBS Turret press. The chargemaster automatically starts a new cycle when the digital scale zeros. So ... by the time I dump the charge, replace the pan (the digital scale then zeros and starts loading the next dump), size the brass, seat and crimp the bullet remove the finished round the chargemaster is waiting on me.
Pretty fast I think. I think a progressive press may lend its self to a little wait, since they are faster than Turrets (I assume).
I think I can drop a straight wall pistol reload about every tweny seconds. Rifle would be a tad slower, I'm a little anal about them. I like consistancy in my rifle reloads. So like WhattaBurger ..... I do them one at a time. After all; I use them for hunting and I want accuracy and a humane kill. I wouldn't want to settle for less.
I load, 9mm Luger, 38 and 40 S&W, 38 Special, 357, 45ACP, 45 Colt, 223, 243 and 30-06