A grenade launcher is a weapon that launches a grenade with more accuracy, higher velocity and to greater distances than a soldier could throw it by hand. Grenade launchers can come in various forms and types from pistols to fully automatic machine-gun variants, all being man-portable weapons firing grenade rounds.
The grenade rifle, as implied by its name, launches 40mm grenades at a respectable distance. Although it has a longer range than regular hand grenades, its ammo lacks explosive punch, so it does less damage than a regular grenade. It's break-action, so to reload it, you need to crack it open and load another grenade after every shot.
The 25mm grenade APW (anti-personnel weapon) is a semi-automatic grenade launcher. It gives you the death-dealing capability of the grenade machinegun in a more portable package. Specifically, this package contains a stock magazine capacity of six grenades, a brisk rate of fire, and decent accuracy.
The grenade machinegun is a very powerful weapon that fires a slew of grenades at incredible speed. While it's not the most powerful weapon, it can still chew apart almost anything thrown at you. It has a computer screen that appears to be used to monitor the weapon's feed system.