stainless hunting rifles are not always stainless

[brownbear53]

General misconception amongst people that don't do their research on the subject.
Stainless refers to Stain LESS, not Stain PROOF
Stainless usually refers to added rust resistance, lots of way to make a metal rust resistant. It does not always have to be a high chromium stainless metal like the ones found in kitchen equipment (that is extremely shiny in appearance)

Any metal that includes more than 10% chromium is a stainless, be it black, silver or pink in appearance. Your barrel is still a stainless barrel, it has over 10% chromium, but it also has a lot of carbon to give it its hardness. This means the the appearance will still be darker (not silver) while retaining higher rust resistance than the non SS version.
In order to appease the buyer, many companies will apply a coating or finish to further improve this appearance and give it a surface protectant like you mentioned. This also helps visually distinguish the rifle on the shelf.

No lying happening, you are just misinformed, a plated shotgun sold to you is still less likely to rust than the generic one, so by definition it is 100% accurate when marketed as "stainless"

 

[FLHTCUI]

Stainless steel is an alloy of mixed metals. It is not always the same mixture thus gives different results.

Popular grades of SS Popular Steel Grades: 303, 304, and 316 then there is 416 SS and 4140 Chrome Moly .
What Grade of SS is used in firearms not to mention each manufacturer uses is beyond me.
My Browning SS A-Bolt I was magnetic...
In my opinion the question to ask is what Grade of SS does each firearms manufactures use and to what extent in the firearm is the SS ?

 

[The Kurgan]

I know I might be stirring the pot on this discussion a bit, but it's my understanding the NATO does not use stainless on their combat arms:

It's not as tough/hard as carbon steel and it galls with sliding/friction. Despite its corrosion resistance, it's actually a quite sub par material for firearms. About the only time I'll give it a slide is in manual action firearms like bolt guns and lever guns. Things like Aluminum and lightweight steel barrels are better because the coatings we use for them make them very corrosion resistant and they have the benefit of strength/weight and longevity.