Most newer generation Glocks can shoot the .357sig in a .40S&W with a simple barrel change. You can use the same magazines. The same is true for shooting .40 in a .357 Sig. This is true with Sig Sauer guns as well. I have a Glock 23 (.40 S&W). I simple install the Glock 32 barrel (.357 Sig) which I purchased for $100. I can shoot .357 sig out of the same gun. The magazines (at least for Glock) for the .40 and .357 sig are interchangeable. You CANNOT safely shoot a .40 out of a .357 sig barrel or vice versa. A barrel swap is required. If you load a .357 Sig round into a barrel chambered in .40 S&W, it could fire, but it would probably cause damage to the gun and won't be accurate. .357 Sig has better "terminal performance" than the .40, but the .40 shells cost less which translates into more practice for the same $$$ with the .40, and better self defense with the .357.