hello,
i have information regarding the birmingham proof marks on this gun.
1....the BP,NP,BV all with crown used 1904-1925 proof also 1925-1954.
2....choke and 12 over c in diamond both used proof periods as above.
3....nitro proof 1 1/8 used 1925-54( in previous proof periods the 1 1/8 suffixed with max or shot)
4...HOWEVER,proof period 1925-54 should have chamber length
marked in inches eg 2 1/2" as well as 12 over c in diamond.
using the above information i would date proof as the change over between old period ending and new beginning 1925,
hence appx 1925.
i do not claim to be certain of the above info but i have interpreted the date charts as well as i am able and hope i have been of a little help.
cheers
mrwmartin
