It is not stainless, although I think the slide action assembly may be stainless. It is nickle plated and shines like new without a mark on it. The attachments I installed are all lined with either Teflon tape or mole skin so as not to mar the finish
I had a close friend with a very nice collection. He got cancer and was gone in 6 weeks. He left me (my choice) of guns and his wife insisted I collect. I actually took the Mariner because it was the least expensive gun he had and I figured his wife would need the money from selling the rest. I helped her sell the stuff through a local gun store. Now I'm glad I took it, it will never be fired as long as I have it.
Interesting note: When I took the weapon, I checked it and it was loaded, one in chamber, safety NOT ON! Also one round in the magazine tube was in backwards. Go figure.....the owner was x-military and a pro. someone other than he must have been screwing with it or his medicine had an impact on his thought process. A great lesson here...every gun you touch is loaded all the time!
If I figure out how to post a photo or 2 , I will.