Designating a bullet with a metal (usually copper or other alloy) casing which fully surrounds the lead or other core material; abbreviated FMJ.
The usage of full-metal-jacket bullets in military contexts arose in part due to the declaration concerning expanding bullets (IV, 3) of the Hague Peace Conference of 1899. This declaration prohibited bullets in warfare with partial metal casings, as these would expand or flatten on entering the human body and cause unnecessarily severe wounds.
Usually without hyphens. A metal casing which fully surrounds the lead or other core material of a bullet.
Late 19th century; earliest use found in Recreation. From full + metal jacket.