Yeah, the paint bullet is .30", and the back-end is a 9mm cartridge dimensions... just like a .30 mauser... I'd like to test that to see how far the 'fool-proof' goes. I'd like to see the look on the Geezers faces when THAT comes out the end of my Broomhandle!
I've been to the factory in Quebec that makes these (A part of SNC-Lavalin or IVI for you old die-hards) and they ARE pretty cool. The chambers for the conversion kits have cut-outs, if I recall correctly, so that EVEN if you manage to jam in a real round, the cartridge isn't supported properly and the case ruptures out the side instead of sending the bullet squeezed down the barrel. I got to fire a full-auto MP-5 conversion kit, (albeit only at the wall in the shop/factory) and it was pretty cool. The sales-guy said when he goes to try and sell this to an agency, he puts on a padded suit and dances around on the range and lets the agency reps shoot away at him. Having seen what they do, I'd say that's a tough way to make a living...