Uhhh, Soo Stupid!
I built a cheap block trigger, with a red firing pin (sorta like the one in the picture) and shot his hand from a good distance (6 feet) and he started crying. Get This- The gun had two really stretchy elastics on it, and it couldn't even shoot across my room! I shot my hand from 0.5 feet and hardly felt it! Now my knex is taken away!