Hammer 12B or 11 gauge

[George M. Purtill Member #28]

I was looking at a friend's lifter hammer gun today and it had the following stampings on the flats:

F9R
B25XX (seriel number)

What do these stand for?

[Hammer Gun]

George, The F9R I have seen many times, the early ser numbers were often seen with a letter from the alphabet in front of the number i.e. B258, do not know the reason for either so the mystery continues Gary

[Bruce A Lyons]

I HAVE 2133. FLATS SAY F9R O2133. IVE READ NOBODY KNOWS WHAT THEY MEAN.

[Bruce A Lyons]

IF YOU GIVE THE FULL SERIAL NUMBER I WILL SEE IF ITS IN THE SERIALIZATION BOOK

[Dean Romig]

On the early lifters the serial number is on the water table, the forend iron, the trigger guard and the side of the barrel lug. The number on the barrel flats is the Order Number, not the serial number.

What is the nominal bore diameter on this gun?