Bluing touchup winchester 9422
I've got a win 9422 made in 1972 that had a spot of rust about the size of a pencil eraser on the receiver. After I polished it out with 400 paper I tried several cold blues including 44-40, both liquid and paste, Caseys Perma and Super Blue, Vans, Blue wonder. None seem to work. I also tried heat with no luck. What type of metal was used then.