[USArmyE4]

I got a Glock 27 to replace the Glock 33, can i use my same G33 Mags with the G27?

Because the .357sig is just a necked down .40S&W.... Am I making a big mistake?

I did notice that the openings at the top of the mags were just a little bit different and the notch where the primer of the cartridge can be seen is shaped a little different as well.

[JR]

The simple answer: Yes you can use a G27 40 S&W magazine to feed your G33 357 pistol.

"however"

We recommend you use the correct magazine at all times. G27 mag for 40 ammo and a G33 mag for 357 ammo. This will help you keep your ammo straight and avoid accidentally shooting the wrong ammo out of the wrong barrel. It is very difficult to identify which round is in the mag at a glance. I have seen it happen and done it myself, shot 9 out of a 40 barrel, shot 357 out of a 40 barrel, shot 40 out of a 45 barrel. Avoid the issue by keeping your ammo separated and loading the correct ammo in the correct magazine. Its cheap insurance.