First, the 9x18 is the 9mm Makarov. Despite the name it is NOT 9mm. It is a 9.2 mm bullet in a 9.91 case.
9x19 is 9mm Parabellum- it is a 9.01mm bullet in a 9.65mm case.
It SHOULD be too fat to chamber, and too short to headspace properly. The energy is lower that a parabellum, made for use in a blowback pistol, not a locked breech pistol. If it DID chamber and DID fire, would likely not cycle action.
Really bad idea.