An ammunition feed adapter and method of use is provided that converts a semi-automatic or fully automatic firearm from a magazine-fed firearm into a belt-fed firearm enabling the firearm to be used as a sustainable source of firepower. Modification of a soldier's standard issue automatic or semi-automatic rifle into a belt-fed firearm increases the options for strategic maneuvering of a combat unit on the field of battle by overcoming the limitations of traditional sources of sustained firepower, such as a Squad Automatic Firearm.