You can also go for spray & pray and buy a drummag. Fill the mag with about 2500 bb's and spray spray spray!
SRC C-Mag G36 2000rds
A&K M249 Box Mag (2400BB's)
SRC AK Drum mag (2500 BB's)
Clasic Army Boxmag M249 1200rds Woodland
Woodland Camo cover included
Clasic Army Boxmag M249 1200rds Desert
Desert Camo cover included