You guys are over thinking this. I'm uploading some pics into photobucket of my trap. It's cheap, simple, reusable, and bullets are recovered in one piece....no dust.

Trap, front view


Top/side view with top door open. Inside is 90# of rubber mulch


Back view with arresting plate (old umbrella stand 1/4" thick) dented from my 185gr Beartooth bullet round I use on boars...dents occured after bullet penetrated 24" of mulch


Overall view. The target would equate to a head shot on a 6" person. You can make it whatever height you wish.



Bullets are collected via using shop vac without attachment. The mulch gets sucked, most of the bullets drop out. You could just dump the mulch into salt water to make the rubber float and lead sink. The mulch does a decent job at predicting expansion and penetration, so long as there are no other bullets to crash into each other.

Here are what some of the recovered bullets look like.