[m657]

got an otherwise nice M31 from an old buddy....he had put it away in a box somewhere for a couple decades after putting a few dozen rounds thru it....we found some kind of rough corrosion on the external part of the cylinder. Sort of large pits, which cleaned up fine...except they are, well, large pits. Cosmetics aside, I don't think they represent any safety hazard. Still, I'm curious about what to do....I'd post photos but my camera is on the blink.

This is a little like an old hunk of iron laying around that developed some signs of aging.

 

[kritter]

it's hard to say with out actually seeing it but.. you can either buff , file ,sand, rebuff , and reblue....or find and install a replacement cylinder or , just live with it..
it's difficult to say what caused it in the first place,, but i have seen gun's that have spent most of their lives sitting in a dresser drawer.. looking just like the day they came home, except where the wood had contacted the metal..moisture from the wood had caused the same condition you discribe.