Maxinquaye:
They don't load and/or shoot as much as you and I do, evidently.
I load my .38match wadcutters/semiwadcutters or 9mm w/115jhps in quantities of 1,000 or more and after sometimes tumbling/vibrating them to remove excess lube, dump them into an empty .50BMG can w/cardboard lining in bottom. Emptys go into another can, and then back into tumbler when full.
I can't imagine anyone shooting 300-500+rds a day at a match with a .500 however!! (two 1500's; dististinguished revolver., service rev., service auto, dististinguished auto, and occasionally off-duty revolver. Indeed, a day full of shooting!)
So, to keep them separated , the 20-50rd boxes must be convienent.