M31 HEAT rifle grenade

M31 HEAT rifle grenade
M31 HEAT rifle grenade fitted to an M14 rifle
Type	Anti-armor rifle grenade
Place of origin	United States
Service history
Wars	Cold War
Production history
Designed	late 1950s
Produced	1950s - 1960s
Specifications
Weight	709 g
Length	430 mm
Diameter	66mm/warhead
Effective firing range	115 meters/effective
Maximum firing range	185 meters/maximum
Filling	Composition B
Filling weight	254 g
Detonation mechanism	nose-initiated, base-detonated

External images

Drawings and Cutaways of M31 HEAT

Dimensions drawing of M31 HEAT rifle grenade

Cutaway drawing of M31 HEAT rifle grenade

The M31 HEAT is a fin-stabilized anti-tank rifle grenade designed in the late 1950s to replace the Belgian ENERGA rifle grenade which was adopted by the US Army and US Marines as an emergency stop-gap measure during the Korean War. Like the ENERGA, it has a nose-initiated, based-detonated HEAT warhead, but unlike the ENERGA, the mechanical impact fuse system is replaced with a less complex and more reliable piezo-electric fuse system which also allows higher angles of impact, up to 65 degrees. On impact, the nose cover collapses, crushing a crystal-like material, which sends an electric current through a separate wire to the warhead's detonator, located in the base of the warhead. A mechanical safety, comprising a set back system located in the warhead's base, grounds the firing circuit and prevents the accidental explosion of the warhead. On firing, the sudden launch acceleration causes the set-back's three disks to rotate 90 degrees, each in succession to the other, with the rotation of the third disk removing the grounding after approximately 10 meters of flight and completing a firing circuit for the current to flow from the nose to the detonator in the base. Compared to the ENERGA, the M31 is slightly lighter in weight and has a smaller-diameter warhead—i.e. 75mm vs 66mm. Penetration for the M31 is estimated to be 200 mm / 8 inches for steel armor plating and twice that estimate for concrete. The warhead technology developed for the M31 was used for the future M72 LAW antitank rocket.

The M31 was originally designed to be fired only from the M1 Garand, but could be fired from the M14 rifle. To launch the M31, a detachable spigot-type grenade launcher (M7A3 launcher for M1 rifle, and M76 launcher for the M14 rifle) is fitted to the muzzle of the rifle. A M3 ballistic cartridge (two are supplied in the packing container with each grenade and are crimped to indicate the cartridges are only for launching rifle grenades) is loaded into the rifle's chamber. The hollow tail unit of the rifle grenade is fitted over the grenade launcher. Official military manuals recommend that the M31 HEAT be fired from either the standing or kneeling position and that it is only accurate against armored vehicles if fired at extremely close ranges. While claimed to be effective against main battle tanks (except in frontal engagements) and lightly armored vehicles when first introduced, in 1972 the US Army stated in its revised anti-armor warfare manual that the M31 HEAT was only effective against light tanks and thin-skinned vehicles.