The MEI Mercury is a family of medium-range low-impulse 40mm grenade (40×46mmSR) developed by Martin Electronics, Inc. (MEI) that can reach out to 800 meters. The rounds are a fixed type ammunition designed to be fired from a 40 mm Grenade Launcher such as the M79, M203, M320 (attached to the M16 rifle or M4 carbine), or Milkor MK-1.