I think there was even one more evolution where the plastic caps came in a strip instead of a ring. The strip was put in a magazine that slid into the bottom of the pistol. Most of them just moved the strip up as they fired, but if I recall correctly there were even ones that cut each cap off individually after firing it and ejected it like an empty shell. Awful for litter, but pretty cool for cap gun technology. I am pretty sure all of this stuff has been banned where I live.