During WW2 and Korea., American arsenals made billions of rounds of steel jacket for issue to the troops.
I will have to check on this. I don't think we did. Not "billions of rounds, anyway. I know the other side did.
As far as steel cased .45ACP, as far as I can find out, the US produced steel cased .45ACP ammo only in 1943, and only from one (EC) plant. There were possibly, other small runs of steel but nothing that was general issue.
What is interesting to note is that while, at the height of WWII we (essentially) experimented with steel case ammo, it was not adopted as standard, and in 1944, with the war still raging, we dropped manufacture of steel cased ammo.
Why do you think that might be?
Axis nations used a lot of steel cased ammo, our "allies at the time" the Soviet Union did. All nations used some quantity of steel cored ammo (AP, usually) and some used steel jacketed ammo in quantity.
That being said, it is worth remembering that what the military does, and finds acceptable and useful is NOT necessarily a good thing for civilian shooters.
The phrase "close enough for government work" applies to the military A LOT.
They don't particularly care if a certain ammo is hard on the guns or if it wears things out faster, as long as it works well enough to do the mission. Cost of repair isn't an issue with anyone until it impacts the mission.
There are service life standards, but these are rarely reached in small arms, and based on my experience inside the Army's Small Arms repair system in the 70s, said standards are rarely even checked, and accuracy is not one of the few that is checked. And the service is fine with that.
As an illustration, there is a standard of accuracy for overseas shipment. For the M16A1, it was 8 MOA. EIGHT minute of angle. How many of you AR owners would be happy if your AR won't shoot better than 8 MOA???
If the M16A1 wouldn't do 8MOA (or better) the Army would not approve its shipment overseas. Guns that failed to do 8 MOA were to be retained in the States for training use.
Now, here's the rub, units being deployed NEVER had their M16s tested to see if they met or failed to meet that standard. (if anyone can come up with proof any of them ever were, I'll gladly change "never" to "rarely"
)
Serviceability inspections were done (when actually done) without firing or live ammo. Checks might have been done with gauges, though generally this wasn't done, either. Arms in the hands of user units were serviceable (function test only) were put in the conex, and shipped. Unserviceable ones turned in for repair, and/or exchange.
I mention this to point out that A) the military doesn't put the same priority on things that civilian owners do, and that B) even then, our military does not use steel cased ammo.
If you want to shoot steel cased stuff to save a few $, go ahead, its your gun and your wallet. It PROBABLY won't hurt your gun. You PROBABLY won't shoot enough that the different rate of wear will have any practical effect.
I'm a reloader, and I LIKE my guns. I don't shoot steel, and I'm not going to.