Bluetrain, That is a mell of a question..
Would SWAG it was original for war wagon, because there were few reproductions made at that time. In the 60s Surplus ones could be had fairly cheap for movie rent,, But That would be one heck of a cool research job to find out the Origin and now resting place of the "War Wagon's " Gatling
Heck in 1945 you could still buy them from Bannersman Sons
Was re-watching the War Wagon the other day when the evil rancher climbs up into the turret to fire the gun, Then they flash outside for the gun shooting up the fence scene. you will see there is no room to mount the magazine into the gun while into the turret..