The Mk 20 Mod 0 was a belt-fed automatic grenade launcher manufactured by NOS Louisville and used during the Vietnam War by the U.S. Navy.
Used by the U.S. Navy Special Boat Units during the Vietnam War, the Mk 20 Mod 0 has since been phased out in favor of the more powerful Mk 19 Mod 3 due to its complexity.
Two known examples of the weapon are on exhibit at the War Remnants Museum in Ho Chi Minh City.
An attempt to improve upon the Mk 18 Mod 0 grenade launcher, the Mk 20 Mod 0 is a blow forward-operated weapon that fires in semi-automatic and in full-auto at a cyclic rate of 250 to 275 rounds per minute.
As with the Mk 18 Mod 0, the weapon is belt-fed, and the ammo belt is fed into the weapon from the left-hand side. The cover above the feedway guides the incoming rounds, with a star wheel in the feedway moving them through the weapon. The barrel was cocked (moved forward), and the feed pawls indexed the round into the firing position. When the weapon was ready to fire, the barrel was cocked. When the Mk 20 Mod 0 is cleared and unloaded, the barrel retraced inside the barrel support.
The weapon has paired spade grips similar to the M2 heavy machine gun with a firing button in between them. When the weapon is fired, the barrel moves rearward, chambering the round and firing it. The barrel blows forward, re-cocking the weapon and loading the next round to be fired.
The Mk 20 Mod 0 uses the same steel disintegrating link belts as the Mk 19 grenade launcher. The weapon's receiver was a sheet metal cover that attached to the backplate and barrel support via Allen-head screws.
The weapon had proven to have a low recoil, low enough that it could be wielded in a soldier's hands for short bursts.
The designers were considering on developing a lightweight model of the Mk 20 with a buttstock and a tripod, but this never came to fruition.
The Mk 20 Mod 0 uses the same 40×46mm grenade rounds as the Mk 18 Mod 0.
- Blow forward
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- Wikipedia article on the Mk 20 Mod 0
- Warboats.org: Ordnance Notes by Bob Stoner GMCM (SW) Ret. on the NOS Louisville Mk 20 Mod 0 Automatic 40mm Grenade Launcher
- Mk 20 Mod 0 at FirearmsWorld.net (Chinese)