John,
I just read your old thread, very interesting.

What caught my eye was that your rifle was “Made for P. Orr & Sons, Madras & Rangoon”.
I have recently acquired a Cogswell & Harrison Certus rifle in .450/.400 3 1/4” that is also marked; “Made for P. Orr & Sons, Madras & Rangoon” in line with the usual Cogswell & Harrison line on the barrel.

Don’t see too many guns and rifles here with the P. Orr & Sons marking. Perhaps more commonly found in Oz?
- Mike