i bought a new remmy 870 , one of those combo packages with a rifled slug barrel and a 26 inch vented bird barrel.
mine has the laminate stocks and that lightly textured flat black finish on both barrels and the receiver.
i dont know for sure, i read on some shotgun site, which i tried to recall that the finish is a sprayed on phosphate and baked finish
i have had my 870 for 1 full hunting season and now im into the next small game season with it ..
i had determined that i dont like it. its not very rust resistant and it mars easily.
i went to the local auto parts store and got a can of textured trunk / truck bed liner spray for my truck and i used the remainder on my NEF project.
its really durable but too thick, it get me some problems..
i got other ideas for my 870. i wont touch the barrels for now, but the mag tube and receiver are going to get a good coat of dura-coat , in the mossy green.
you could use flat black in dura-coat , if you are looking for a good solid durable finish. if you really need to replicate the remington finish
you may have a hard time finding just the right product.