I'm sure the .50 cal is a replica. A gentleman scratch built a replica .50 cal for the TBM Avenger that I did some work on. He went to visit the Army's museum at Aberdeen, Maryland, where Richard Atwater (the guy you see on all the various History Channel documentaries) showed him several models of the "Ma Deuce" and he chose the one that he thought most closely matched the one that equipped the Avenger. The .30 cal in the radio compartment was also a replica, but that one was purchased from someone who produces replica machine guns for that purpose.