I was using indirect fire as an example, but yes, volley fire was used that way. It was used in direct fire as well, but as for aimed fire against a specific individual soldier, I doubt any army ever used volley fire that way; it is about impossible to even see a man-size target at over 2500 yards, let alone score hits.
FWIW, the standard combat load for the Thompson was five 20 round magazines, two 50 round drums, or six 30 round magazines; for the M3/M3A1 SMG, it was six 30 round magazines. In practice, many SMG-armed soldiers carried as much ammo or as many extra magazines as they could manage.
American troops were not generally issued drums, in part because they won't fit the M1 and M1A1 Thompsons; the British used 50 round drums, but AFAIK, no 100 round drums were issued by any army in WWII (though certain Chicago "soldiers" were said to like them). BTW, the TSMG magazines are designated by rounds in Roman numerals, XX, XXX, L, and C.