US Cartridge, 40mm Multiple Projectile, M576, XM576E1
This cartridge is intended for use in counter-insurgency and conventional operations in jungle environments, particularly during periods of poor visibility where personnel targets appear at short distances without warning and are vulnerably exposed only fleetingly. It is designed to be fired from 40mm Grenade Launchers M79 and M203 (attached to the M16 series rifle).
The cartridge is a fixed round of ammunition consisting of a multiple projectile assembly and a cartridge case assembly. The projectile assembly includes a polyethylene sabot carrier with one center cavity and several smaller cavities around the outside perimeter, A plastic pellet cup filled with 20 metal pellets is fitted into the center cavity and is covered by a snap on cap. The outer cavities act as air scoops. An obturator on the rear of the sabot serves as a propellant gas seal between the cartridge case and the sabot.
The projectile assembly is crimped into the cartridge case. The case is a hollow bichambered cylinder with a metal closing plug crimped into the open well of the propellant chamber in the cartridge base. The propellant chamber acts as a high-pressure chamber and has ten vent holes in the top sealed by a copper disk. The upper hollow cavity in the case serves as a low pressure chamber. A percussion primer is crimped into a center opening in the closing plug.
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Collaborative Ordnance Data Repository