WD 40 won't hurt blueing or case colors! It is a very good rust preventive that builds a protective film. It is a very poor lube and the film it builds to prevent rust gums things up on the inside.
bill
"And it soaks into wood and it gums up moving parts, and once it gums, you darn near can't get it off".
I'm sorry but that WD-40 crap has hurt more guns than the law should allow. They should be required to put warning labels on that junk.
I start slow and if need be, get a little more agressive with rust removal. Start with a cotton washcloth and CLP oil, Next I go to a peiece of oak tan leather, with oil. If this does not get it, then no matter what you use next it's going to show pitting.
