We use a mix of caliber and mm like 32 acp,380 acp, 45 acp, 40 s&w, 223\5.56,308\7.62, 22 caliber(lr, Magnum,hornet) and some are only in mm like 9 and 10 mm 6.5 mm and other ones of European origin
@sralius, 380 is a 9x17 bullet in Europe called 9mm short or Browning but in the us it's always called 380, also 45 acp is always called 45 because it's mainly a American round but it's technically a 11 mm bullet.
Oddly enough there was a point where we were close to converting, even being as far as having our signs be metric but our president at the time decided to change it
Hey we use it for more than ammo! We also gotta weigh our drugs