Mk 19

The Mk 19 is an automatic 40mm grenade launcher originally designed to be used on U.S. Navy patrol boats during Vietnam, but was adopted by the entire military.

Call of Duty 4: Modern Warfare
In Call of Duty 4: Modern Warfare the Mk 19 is a helicopter-mounted grenade launcher available in the level Shock and Awe, it cannot be moved by the player but is mobile as the helicopter it is mounted on moves. It has a medium rate of fire. The Mk 19 is prone to overheating and this is visible on the HUD through a bar that fills with red color when the gun is fired. It is an explosive weapon and can take out tanks, troops and anti-aircraft emplacements easily.

The Mk 19 also has the slightly ironic ability to fire 19 grenades in a row (holding the trigger down) before overheating.

Mk 19 uses a longer 40mm grenade than the M203,and also fires the grenade round at higher velocity than M203 grenade round,so Mk 19 ammunition cannot be used in the M203 grenade launcher despite having the same diameter.

Tanks take 2 shots before they explode.

It is possible to blow up oil tankers with the Mk 19. Strangely, tanker explosions do not destroy nearby tanks, and tend to only obscure your vision. It is also possible that the tanks will take 1 shot to make it explode.You have to aim carefully though.

Strangely enough the grenade fired will travel completely straight and never arch, unlike an actual Mark 19, this has proven for amazing accuracy.

Strangely, if you fire grenades at friendly helicopters and tanks, they will not explode.