I had an old bag of charcoal briquettes. I never use them because I have a gas grill now. To be honest I don't know why I kept them. I took them out shooting one day and set them up on spent shotgun shells like golf balls on tees. I set them up all over the place and it was great. They turn into black wisps of smoke when you hit them and they are cheap.
Someday someone may kill you with your own gun, but they should have to beat you to death with it because it is empty.