The Grenade Launcher is the Duke Nukem 64 alternative to the RPG. The weapon fires projectiles similar to that of the Battlelord mortars. It has enough damage to kill a Pig Cop, although a octabrain may require more than one shot. It has the same fire rate as the RPG. It bounces off walls, and can be used to strategically kill enemies that aren't aware of Duke's presence. It's maximum ammo amount is 48, close to that of the RPG, although every ammo item is worth 12 grenades, which basically means that the players has a much expense repertory of grenades compared to the RPG.
The Grenade Launcher has a blue-like texture pretty much similar to the pistol, shotgun and Missile Launcher ammo, which all have a red-like counter-part for the sub-ammo. No coincidence, using a hex editor there can be found unused quotes along with the three sub-ammo:
EXPLOSIVE SHOTGUN SHELLS!