The 1st box that you showed is made different than the 3rd. It's easy to tell the difference, just look at the corners. The ring is actually part of a lock system for that type of can. A 2-pronged pin was also on that ring, if you look closely there are tiny holes in the metal flap. The pin was put into those tiny holes sideways to prevent the lid from opening. I have examples of both 50 cal boxes and I always thought that the box without the sharp corners were made during WW2 and the one with the sharp edges were made after WW2 and during the Korean War. Get yourself some wire thin enough to go sideways into those holes on the metal flap and wrap one end around that ring. Keep it loose so it can still move around the ring and then you will understand the purpose of the ring. With that other part it's a lock.
The 1st box that you showed is made different than the 3rd. It's easy to tell the difference, just look at the corners. The ring is actually part of a lock system for that type of can. A 2-pronged pin was also on that ring, if you look closely there are tiny holes in the metal flap. The pin was put into those tiny holes sideways to prevent the lid from opening. I have examples of both 50 cal boxes and I always thought that the box without the sharp corners were made during WW2 and the one with the sharp edges were made after WW2 and during the Korean War. Get yourself some wire thin enough to go sideways into those holes on the metal flap and wrap one end around that ring. Keep it loose so it can still move around the ring and then you will understand the purpose of the ring. With that other part it's a lock.
Ammo boxes are pretty rad
Heak yeah !