my first gun, bought a couple years ago, a Tanfoglio Witness P, (im told this is a CZ clone?) with a composite frame. Bought a second mag for a .40 witness but it never fit right, engaged the mag release but could slip out. Closer inspection the new mag is slightly shorter (front to back) than the mag that came with the gun - and .40 rounds slip back and forth about 3/16 inch in the original mag. No play in the new mag. The barrel is marked .40 S&W. I recently learned .40 and 10mm differ only in length of the cartridge. so whats the deal? Is this really a 10mm gun i have been firing .40 through? Or is it just a b**tard? Can i fire 10mm through a .40 barrel? Or do i just have a bunch of mismatched gun parts to get rid of?