[slang]

That's true and a good suggestion.

Stopping the bullets/coin is one part of the challenge, keeping it within a given area another, and finding it still another.

At the velocities normally associated with firearms projectiles, the bullet/coin often bounces around where one would not expect. At full velocity and energy they might bury into the ground. Having hit something like particle board first and slowing down slightly, they may just bounce.

The whole practice is better done on some controlled lab with gellatine but those of us geeky enough to want to do this dont normally have that type of access.