I don't believe that with the "nines" you can convert to .40 or .357 SIG without using a completely new slide assembly. As the hole in the slide for the barrel is smaller in diameter and will not accept the larger diameter .40 and .357 SIG barrels. Just the opposite is true for the guns initially designed for the .40/.357 SIG because
With Glock, a 40 such as the 23 will except the Glock 32 barrel (357sig) and I'm sure other models will do the same. Only the barrel needs to be changed. I don't know about 9mm though. Never check that."