Dunno what made me think of this just now. When I worked for IT in a school district way back in the 90s, a librarian told me she kept a supply of mouse balls in her desk because kids would steal them out of the school computers. What I remember about those balls was they picked up dust and crud off surfaces. Pretty soon optical mice came along and they were history.
Turns out you could use an xacto and carve the rubber coating off and the steel ball was a perfect fit for a paintball gun. No winners had there.
Jesus, could that actually kill someone?
Nah, it didn’t have enough oomph to break skin but it left nasty bruises. It could have claimed an eye or teeth though