I carry for work, but not a SIG, usually a Glock 22 or a 1911, plus
another handgun for backup. The Sig P226 is a nice pistol, though. I'm
not sure what you are trying to gain by fitting it with a 22 slide and
works. The recoil, muzzle flip and noise will be totally different
between the two rounds and at distance at a target, so will the impact of
gravity, so you won't be gaining the shooting skills you want with a 40,
45 or even a 9 round in a defense pistol by running 22s through it. I've
tried a few of these combos at the range. They were fun but shooting 22
rounds isn't going to help you become proficient firing larger rounds in
the same basic pistol.