MP40 rust?

[Scallopking]

Is this rusting? It didn’t wipe off. Didn’t smell like rust. It’s only on one side.

 

[*GAREEF*]

If you take a moist que tip or paper towel and wipe it and nothing is coming off at all, I’d say it’s from heat a type of blueing from lubricant or mineral deposits.

 

[Scallopking]

Thanks for your reply. That must be the cause. Nothing came off. Of course I freaked out little seeing it. I’ll take my other apart and see what that looks like. This one has been making noise so wonder if what rubbbing cause the heat.