Wax bullets can cause a serious injury. I've shot wax from a .44 Remington with a cap and maybe 4 grains of 3f and it would penetrate a piece of Masonite. It would take considerably more powder to force a wax bullet the length of a rifle barrel. If you have a cookoff while loading just the powder alone can cause injury if your hand is over the muzzle. Any projectile can do damage that close. The paintballs I'm familiar with are about .40 caliber and are fairly tough but I don't know if they are strong enough to stand being shot and ramming them down might bust them.