[KP95DAO]

I picked up some 357 Mag brass that had this on the headstamp:
BHA 357 MAG PROOF.

The case was regular brass colored and the primer was copper colored and very flattened.

What do you know about these cases?

[jerryd]

Maybe Black Hills Ammo?

[Jim Watson]

BHA is the Black Hills headstamp.
"Proof" means it was a high-pressure proof round, about a 30% overload for the purpose of testing a new or major overhauled gun. Normally fired one per gun or one per chamber at the most. Anybody who scrounged a bunch and was using them for plinking was heavily stressing his gun. Might have been reloads in proof brass but the flat primer indicates they may well have been real proof loads. Not smart.
I wouldn't use them for full charge reloads, brass life would probably be short. I wouldn't use them at all unless I had a LOT to use for mild practice ammo. Just playing safe, brass is cheap.

[happy old sailor]

JW has it right. brass is cheap, play it safe.