AFAIK all US produced 45acp ammo of WW2 date is corrosive. It's the primer that causes the problem after ignition.
Corrosive is what it is,,mildly corrosive is what the marketers have often put it out for sale as.
If the ammo is still in it's original box and full,,it's probably worth more to a collector than to shoot. Maybe one of them I'd trade you two boxes of commercial FMJ for the WW2 box.
The salt compound left behind as a result of firing will absorb water from the air. That will cause rust to form and in most cases quickly pit the metal surfaces it is on. The bore of course is the major concern, but any other surface that may have smoke/powder debris from firing is of concern.
As soon as possible after firing any corrosive ammo,,(and don't delay to tomorrow as it will be rust by then in most cases), strip it down and clean it with something that will disolve the corrosive salts and rinse them away. Then the surfaces can be dried and oiled for protection.
If just cleaned with oil over the top of the corrosive salts,,it'll rust underneath and cause the same problem as if you didn't clean it at all.
Many methods exist for the chore,,everyone seems to have a favorite. The Gov'mnt made special bore cleaner for it. Hot soapy water is often used.
Myself, I've used a brush then patches soaked with Windex. Followed by dry patches,,followed by patches w/WD-40. Then let it set overnite to check for after rust. If clear,the real oil goes into the bore. Recheck again just to be sure.
Surfaces other than the bore can be wiped off with what ever stuff you choose to use, dried just like the bore and treated the same.
I've done it this way for probably 50yrs and haven't lost a bore yet to rust from corrosive ammo and I shoot a lot of it. Still too in my M1 .
