M576 40mm grenade
Encyclopedia
The M576 is a US Army designation for a type of 40mm grenade cartridge. The M576 is a buckshot load for the M79
M79 grenade launcher
The M79 grenade launcher is a single-shot, shoulder-fired, break-action grenade launcher that fires a 40x46mm grenade which used what the US Army called the High-Low Propulsion System to keep recoil forces low, and first appeared during the Vietnam War...

, M203
M203 grenade launcher
The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

 M320 and M32 MGL grenade launchers. It was designed to give the soldier carrying a grenade launcher a powerful cartridge for close-quarters combat such as found in clearing buildings, bunkers, and trenches, as well as thick vegetation.

When 40 mm M79 grenade launcher was first developed, the weapon was to be the primary weapon of the infantryman carrying it. It was quickly found that in most engagements while the grenadier gave the squad a decided force multiplier, they were also decidedly exposed if presented with an enemy within the arming distance of most high explosive rounds. Even rounds with a shorter arming distance presented significant danger to the shooter if used at those ranges. Prior to development of grenade launchers attached to standard infantry rifles, development commenced on non-explosive cartridges to allow those armed with launchers to engage targets at shorter ranges safely.

The M576 contains twenty 24g metal pellets. The XM576/XM576E1 was standardized to become the M576. Normal dispersion pattern of the M576 will put 13 of 20 pellets in a 1.5 meter circle at 40 meters. The remaining 7 pellets could be anywhere. Another test variant, the XM576E2, which had twenty seven, 24g metal pellets without a sabot within the shot cup was deemed to spread too quickly for effective use. Both types had a muzzle velocity of roughly 880 ft/s (268 m/s).

By comparison, A 12-gauge Winchester AA Super-X Buckshot (XB1200) shell is loaded with 9 pellets of 00-buck traveling at about 1,325 ft/s (407 m/s).
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