I'm confused. I'm not against handguns but I don't know much about them. seems to me though, that a 40mm pistol would be pretty cumbersome. I remember something in WW2 called a 20mm cannon they used on some aircraft. if cannon shells come in 20 mm, then we have 40mm handguns? should the 40mm Mark mentions be a .40cal vs mm? or did I just miss a gun joke?