40 mm grenade

The 40 mm grenade is a military grenade caliber for grenade launchers in service with many armed forces. There are two main types in service: the 40×46mm, which is a low-velocity round used in hand-held grenade launchers; and the high-velocity 40×53mm, used in mounted and crew-served weapons. The cartridges are not interchangeable. Both 40 mm cartridges use what the US Army during the Vietnam War called the High-Low Propulsion System.

The less powerful 40×46mm is used in hand-held weapons such as the M79, M203, the M320 grenade launcher, and the multi-shot M32 MGL or Zakłady Mechaniczne "Tarnów" SA RGP-40.

The more powerful 40×53mm is used in automatic grenade launchers mounted on tripods, vehicles or helicopters, such as the Mk 19 grenade launcher, the Mk 47 "Striker" 40 mm Grenade Machine Guns (GMGs), the Heckler & Koch GMG or the South African Vektor Y3 AGL. In these roles, the rounds are linked together with a metallic disintegrating link.

A new 40×51mm cartridge recently (2007) developed in South Africa provides a more powerful alternative for hand-held weapons without increased recoil. A new version of the Milkor MGL chambered for the new round remains backward compatible with existing 40×46mm rounds.