To answer some of the questions here, the VAST majority(or at least among the ones I've seen over the years) of the Nitro Hunter shotguns did indeed have nickel plated receivers. BUT, not all. The "most popular" one out there that most of us occasionally see or have as a family heirloom were probably made by Crescent for Belknap. They have a very beefy reciever with sharp corners and a very thick barrel and breech. If you run a google image search, you'll see a picture of the most common one out there. But, like I said above, a lot of other guns from that time period were apparently contracted by Belknap and had the "Nitro Hunter" stamp. So it's nothing to see a Hopkins and Allen, or even a Belgium gun with the Nitro Hunter insignia. As far as the "purplish" receiver some of you are describing, that's probably indeed case hardening (I'd really like to see a picture of one of those) OR it could be something else I have seen. I have a friend who has a very similar shotgun that he had re-blued/re-finished. That receiver now looks very purplish. It's a very pretty finish.