I wouldn't try anything with a gun that only shoots 400 FPS. Paintball guns shoot about 300 FPS, though at a higher caliber... which might cause less damage.

Anyway, off track. Gamo makes single pump air rifles in .177 (and I believe "shotgun" versions). Some of their guns will shoot up to 1200 FPS. They also sell specific ammo that supposedly increases the speed up to 25%. If you're dead bent on getting an air rifle, theoretically you could get one that shoots 1600 FPS.