I may have been wrong about the rust. I tried some Hoppes #9 on it and it is slowly removing it. The patch does not come out dark, not of a red color. I was originally using military bore cleaner, it did not seem to do much to remove it. There is not a lot of it, just a streak or two from mid barrel going toward the muzzle. Plastic?? I do not know what was shot in it, I bought it used and did not notice it at first, the gun looked to have been hardly used.