I'd wager I use about 700-900 BB's for an outdoor game (~4-5 hours). I use real caps though so I really try to conserve ammo when I'm playing. My calculation was 5 real-caps at 25 BB's each (due to "wasted BB's" and such) and about 6-7 full reloads (of all 5 of my mags) for the day.
Indoors I'd assume it would be about the same BB usage unless you really like to hose down hallways and such. It really depends on the player though, much like at paintball fields. You'll see some guys just buy 100 paintballs and be fine running that for the whole day (pump action paintballers who snapshot and actually actively "snipe") then you'll see one guy buy a whole case cause he just hoses down anything that moves with his 15 BPS full auto gun.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE