i once went with less then 200 shots one game with my mp5. Probably when I was forced to shoot semi when my gun was shooting 445. I remember reloading one of my locaps twice the entire day. Highest was 2 whole bags of .25. Roughly 2 Full C-mags. That was a fun day ;D Beware the "WHIRRRRRRRRRRR*click*" of death!
Number of rounds depends on my loadout, how many players in a given situation, and what role I feel like playing that particular day. I would base it by the bag though. I can use 1 and a quarter bags per month on average. I used to keep track.