During a fairly brief period of a couple of years, billions of rounds or .45 steel cased ammunition were turned out.
I don't know if I can accept the amount, "Billions" of steel cased .45s...
Every steel cased US GI .45 I've ever seen or heard of all has the same headstamp, EC 43.
Perhaps some ammo expert can shed more detailed light on the matter, but it seems that the US produced steel cased .45 during ONE year (1943) at ONE plant.
and it may not have been an entire year's volume production.
Millions of rounds, very possible. A billion? perhaps, I'd want verified production numbers to accept that. Billions? as in 2 or more billion? I rather doubt that.
1943 was a tough year, wartime production had ramped up and was in full flood. Rationing of "strategic" materials nationwide. 1943 was the year we made steel pennies. The only year we did that, too.
Steel cases may be the "bees knees" for some things, but go shoot some out of a revolver, and tell us how well that worked!!