It's not safe to shoot someone, it would sting like hell, but it won't hurt your gun. Works best if you drill out the flash hole with a 1/8" drill bit and mark the brass so it never gets loaded with a bullet. Like secondchance said just push the case through a sheet of wax. If you shoot into a box stacked with newspapers or cardboard, you can collect the wax and remelt it. Pour it out so the wax dries in a sheet and you can reuse it. I never made any wax slugs, but I've used my bullet molds to cast bullets made from hot glue, they're called gluelits. The hot glue bullets are even reusable, I shoot into a box filled with rags and it stops them undamaged. It's just a way to shoot your guns out in the garage if you can't get to the range.