Probably early indoctrination, but I like the 600--650 range, myself. This is where most Thompsons operate-- A classic old SMG, not very Tack-tick-cull, but lots of fun.
I've made a bunch of empty brass with MAC-10s and M2 .30 carbines. It just seems like too big a chore to keep magazines loaded . . .
The utility of the SMG in a non-military setting is largely for show and morale purposes. I know - - -You can't have a SWAT team without a couple of buzz guns, but I can't find a time in the past 30 years when they were a real advantage for law enforcement.
FUN shooting, and matches, now - - -That's another thing.
Best,
Johnny