We used to build guns out of Lego which eventually over the years led to our invention of custom Lego crossbows using rubber bands to sling projectiles. Our competition quickly devolved from who could shoot the farthest to who could hit moving targets (each other, cats, etc). After being hit a few times from each other's weapons, we quickly learned it's not fun to be on the receiving end, even if it was just a few grams of plastic.