Steel material with welded seams, made in several different patterns. Rubber gasket under lid makes the box almost waterproof, rubber gaskets are good. WWII
Unsung: The AN/M2 .50-cal. Machine Gun in World War II
WW2 .50 cal Side Open Ammo Box - Omahas Army Navy Surplus
Why do machine guns usually feed into the left side of the gun? - Quora
WW2 50 Cal Ammo Can, World War 2
WW2 .50 cal Side Open Ammo Box - Omahas Army Navy Surplus
May 2023 Premier Firearms & Militaria Auction - Day 1 by PoulinAuctions - Issuu
U.S. Military Surplus Waterproof M2A1 .50 Caliber Ammo Can, Used - 1204, Ammo Boxes & Cans at Sportsman's Guide
WW2 50 Cal Ammo Can, World War 2
Naval Artillery