The other day I hung up an aluminum pop can for the grandkids to shoot so I didn't have to worry about ricochets. Pretty soon the can was looking pretty freyed and I remarked that if they kept it up they would shoot it in two. It wasn't many shots later that the can did fall apart. It had taken surprisingly few shots, on the order of a hundred I would guess. The kids had to take the butcherd can home as a trophy to show their dad.
So, I hung up a larger aluminum iced tea can. Sure enough they shot that one in two pretty quickly too. By the time they killed that one all the adults around were paying attention and cheering them on as those last few raggedy strips seemed to resist all BBs.
This could make a pretty good game if enough BB guns could be rounded up to form some teams. I would guess that two person teams would take about 5 minutes to cut a can. The average time could be adjusted somewhat by the distance they had to shoot.
