I have two .30 ammunition cans, one each of Model M1 and M1A1, both made by United (don’t know who they are - have no real interest in machinegun ammo boxes). I don’t have a clue why one is a “M1” and one is an “M1A1” since the two appear dimensionally and mechanically identical.
At any rate, both are marked for repacked ammunition by Twin Cities Arsenal (TW), the M1A1 box from August 1945. The M1 box has a repack lot number of TW B-82785. It is not dated, or in any way I can read. The M1 can is marked for 250 rounds belted 4 AP M2 to 1 Tracer T10. The M1A1 can date 8-45 is marked for 250 rounds belted 4 Ball M2 to 1 Tracer M1. Both of these cans have the locking latch on one end, I assume to attach to a vehicular mount.
I was in the Army in the late 1950s, and was, for a brief time, a mchinegunner using M1919A4’s in training, but once in a TO&E outfit, the guns were the 1919A6, although we had the tripods and traversing gear for the guns as well, of course. For training our ammunition was belted 250 ball rounds, often in cloth (white and OD-color) belts. Our tactical ammunition was linked 4 ball 1 tracer, although I don’t recall the model of the tracer rounds. The ball was Ball M2. I didn’t see the tactical ammunition much, being peacetime, but seem to recall it was all in metal links. don’t hold me to that. they didn’t like tracers for practice firing as at Fort Ord, Hunter Liggett and Camp Roberts, where all of our training was conducted, depending on the type of exercise, it was very dry in summer and tracers started grass fires. I also recall that there was a specific adminition in our FM on the guns not to fire AP ammo when tanks were involved in the demonstrations - I think they ricocheted like the devil off of tank armor. I suspect that the absence of AP in our belts at the time had to do with the armor of the day - not much in use that a .30-06 AP would worry, and ordinary ball and tracer would pretty well chew up standard automtice (jeeps, trucks, cars) metal. Conjecture on my part - the bujext never came up that I can recall, in any of our training. Of course, I can’t speak for any aerial use of the guns, with which I have zero knowledge and experience. I don’t recall, by the way, every having used one of the cans with the locking latch on the end. Also can’t recall any way they would have latched on to our tripods, or the sides of the guns we had. Haven’t had anything to do with MGs since 1957, so all this is from long ago memory, except the data on the two cans which I currently possess.