I did the same thing with canned tomatos. Gave my six year old a can and a hammer. Every boy believes he is the strongest person in the world. I told him to smack that can as hard as he could, as long as he wanted. After whacking it several times, with just a split seam, I reminded him just how small a .22 LR cartridge was, and popped a Stinger thru a can, with the obvious explosive results. Then I asked him to compare, and tell me which he thought could do more damage, him or a firearm. Gts the point across.