Bore butter may be at fault, I'm not sure but I
have a Remington model 34, that my dad left me
when he passed. I don't know how long he kept
BB in it. But he bought it in 1951. I still use BB
on it and no rust. I also have an AK-47 I
brought back from Nam. It has been stored with
BB in it for many years. And I do mean stored
for it has a working full Auto spring & lever. But
you have got to get rid of all moisture before
applying BB.