I am thanking of getting a g22 and getting a .357 sig and a 9mm barrel for it. Could I just get a g19 and get a .357 and .40 S&W barrel? Are the mags for all 3 calibers interchangeable? And could I put a 10mm barrel and mags in a g21. I'm sure you all can tell I'm new to glocks and don't know much about them. Good thing is I learn very fast.