These Marines will test a lighter, polymer-cased .50 caliber round 1 day ago Your next belt of .50 caliber ammunition could weigh 10 to 20 pounds less than it does now, if industry representatives are able to meet the needs of a recent Marine Corps request. (Staff Sgt. Vitaliy Rusavskiy/Marine Corps) Marines at infantry schools, machine gunner courses and certain amphibious battalions will soon be lugging a lighter load as they test new polymer case .50 caliber ammunition. The Marine Corps has taken the lead to lighten the load of the heavy ammo, its linkages and containers. Brig. Gen. A.J. Pasagian, head of Marine Corps Systems Command, told reporters in an overview of recent and ongoing infantry gear updates that the combined changes that have been made so far have reduced the weight of an ammo can of .50 caliber by a quarter.