Re-blue, but nicely done. I'll bet, without seeing it in person, that someone took it to a higher level of polish than necessary and rust blued it. (320-400x is plenty fine enough and the industry standard today, but if taken to 600-800x a brighter blue is the result. Technically much harder though - when the surface is too highly polished, the bluing solution initially tends to "bead up" and the resulting finish is blotchy. Many more coatings + persistence is required to make the bluing even out, but the end result can be worth it.)
My first thought was someone did a credible job of nitre bluing that receiver but it doesn't compare to the known original in the 2nd pic - unless it's the difference in lighting that's tricking my eye.
Not a great pic, sorry, but this is what 400x grit polish looks like under rust blue. As with the other two pics in this thread, lighting has a lot to do with color interpretation.