I'm looking at a 357 magnum with a model number of M586-1 it looks like it's nickel however the owner says it's stainless. i have a model 586 thats blue and can only find blued guns under the model 586-1 .
You placed an M in the model number. If the M is stamped above the model number, it means that it had the recall modification upgrade. This installed an new firing pin and firing pin bushing. One less thing to worry about.
If it is factory nickel, there sould be a N stamped on the cylinder outside of the extractor star. I beleive the extractor should be blued. There should also be a N stamped on the left side of the backstrap.