If you're using water, a swimming pool is best. If not then then two 55 gal drums welded together will catch most any bullet. Its best to have a removable lid on the barrels with a small hole in the center for firing the firearm. The lid can be removed to recover the bullet.
Its best to paint the inside of the barrel with white paint to make it easy to recover the bullet. Molding clay on the end of a stick is used to recover the bullet.
However, many bullets will be deformed or fragmented. To eliminate this reduced loads should be used.
Pull the bullet with a collet bullet puller. Dump the powder and (for rifles) load 8 gr of bulleye to get consistent velocity. Half charge of rifle powder are in-consistent.
Edit to add: This info is from one of my text books on Firearm Investigation.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071
Last edited by kraigwy; August 6, 2013 at 06:10 PM.