I've been looking at proof marks today but cannot find the kind you mention. There's BM under a crown for British military and an R under crown for re-proof, that's all I can find up to now.
Have you any idea how old your gun is ? I only ask as I believe some U.S. Weapons were brought over to arm the Home guard and other groups because of weapon shortages during ww 2. Could it have been re-proofed for military use over here and eventually found it's way back home in later years ?
I'm very probably completely wrong but other than BNP under a crown, that's all I was able to find in my Brit and foreign lists.
Edit.. Just spoken to a guy who told me that American shotguns were used in WW 1 and may have military proof stamps on, also that some battlefield repaired guns were re stamped.
still may be barking up the wrong tree regarding the marks you mention but even if it's totally unconnected, I learned something new today.
Last edited by El Garro; 10/22/12 04:44 PM.