They work pretty good. Use no 'hi-speed' ammo if your going to be close to it.
Nothing bigger than 22LR, no 22MAG.
Keep the bolts tight, they will loosen after repeated thumping. Wrap a piece of heavy burlap, sheet, cardboard or whatever around it, or fasten it to the front to keep the backsplash of bullet fragments in the trap...it will help to keep the lead dust in the trap also.