The GM 79 is a grenade launcher that appears in the Resident Evil 2 remake.
"Single-round break-action grenade launcher capable for firing both flame and acid rounds. Great for area damage, but slow to reload."
In the UI (while aiming the weapon) or in the inventory screen, it's possible to see what round type is currently equipped based on the color of the small bullet shown (red for flame, yellow for acid).
By default the GM 79 takes up one space in the inventory, but once it's upgraded with the Shoulder Stock (GM 79) it will instead take up two spaces. Upgrading it with the shoulder stock will reduce its recoil and make each projectile travel in a more stable trajectory.
A versatile weapon capable of dealing with multitudes of enemies, from zombies to even the Tyrant and bosses with relative ease. Its mainstay feature of area of effect shots also plays into its strength, capable of hitting multiple targets in close proximity with a single shot. Ammo for it is relatively plentiful.
Its main drawback however is its slow reload speed and low capacity. Being a single shot weapon and needing to reload after every shot makes the sluggish reload speed very prevalent.
A veteran choice weapon when dealing with Birkin's mutations as Acid Rounds are able to stun it consistently, and with propper pacing it's capable of stunlocking the creatures for good until its eventual defeat.