You could, but I wouldn't. If you did (did I already mention that I wouldn't?), you might have to get a weaker recoil spring (or modify the existing one to be a little weaker) if you have some FTEs or FTFs. Also, because these are blowback guns the barrels are fixed. You'd have to have a smith push out the old barrel and press in the new one. This mod would also disqualify the gun as a C&R. Something wrong with the 9x18 barrel?