Afew years ago at a side by side event. I was trolling my Purdey through the tent. I stopped by a well known English gunmaker table and they took a look. They noticed that the flats were blued and commented that they had been re-blacked.
I told them "No" and said that was common on Purdey's.
I imediatley emailed Purdey and asked that question and they quickly responded that it was common on Purdey's to have the barrel flats blacked.

Mike Proctor