Can I shoot 38 special ammo out of a Glock 31 357?

No, you should not shoot .38 Special ammo out of a Glock 31 chambered in .357 Sig. While the .38 Special and .357 Sig cartridges share the same bullet diameter, the .357 Sig operates at a much higher pressure than the .38 Special. Firing a lower-pressure cartridge in a gun designed for higher-pressure ammunition can lead to dangerous malfunctions and potentially catastrophic failures. It is crucial to always use the correct ammunition specified by the manufacturer for your firearm to ensure safe and proper operation.