Is it nickle, or is it just left in the white?
Or polished back to white?
I've seen a number of plated Trap-Doors over the years. Most were from some VFW or Foreign Legion post that had received them "way back when" to be used for ceremonial purposes and they had them plated for their Honor Guard, etc. (I've also seen the same thing done to M1903 Springfields and Garands. Havent seen a plated M16 yet, but I'm sure I will.....