The GP-30 grenade launcher is a weapon built in Russia, where it is normally attached below the barrel of an AK-series assault rifles, and can only be fired when mounted to a rifle. It was issued by SG-4 for off-world operations, including on one particular mission to P3X-367. (SG1: "Metamorphosis")
It has a very short barrel in front of a basic trigger mechanism with minimal hand grip. On top of the barrel is mounting gear to attach the weapon under the barrel of an AK-series assault rifle. The GP-30 does not fire the same rounds as the Colt M203 grenade launcher - in fact, it's a caseless muzzle-loaded weapon.