If you must, do it in your basement.
you can probably setup some sort of catching mechanism to shoot BB's at.
Take a box (cardboard or w/e), turn it sideways, put a towel or something inside to dampen the force of the strike, put a piece of paper in front of the towel (hang it from the front of the box), and you're good to go.
You can also print targets from your computer and use those if you want.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE