Let me clarify a bit. The 9mm will take both the .40 s&w and .357 sig magazines, but depending on what generation magazine you have, the 9mm may or may not work in the .40 s&w and .357 sig. The newest generation of 9mm magazines have a follower that has a high bump on it. This bump will prevent it from chambering a round in a .40 s&w or .357 sig. Here are a few photos that show what I'm talking about:FBMG Smithy said:9mm mags are not interchangeable. .40 and .357sig are. .357sig is just a .40 casing necked down.