I am starting to wander from bore butter... I don't think it is rust, but I hate pulling brown patches out of my bore... Get it "really clean", then take a ballistol soaked patch and it pulls more brown out...
If I have been shooting a lot, I normally do the hot water in a bucket thing, sometimes with just a touch of soap...
If I've just fired a shot or two, I like Bruce's method of diluted simple green followed by denatured alcohol, then ballistol.
Always hit it with the alcohol before loading...