Why not just buy a Glock 17 to begin with? Can's see where there'd be much saving or benefit by purchasing a Glock 22 police trade-in and a 9mm aftermarket barrel and mags. Were it me, I'd go for a 9mm pistol from the git-go rather than fooling around with a .40S&W and converting it to shoot 9mm ammo. No offense, but what you're proposing doesn't make a whole lot of sense. Please tell me what I'm missing.