Kahn,
I have B.S.A Literature covering the period 1925-1937.Your gun as illustrated is seen in the 1925 catalogue but dose not appear in the 1937 catalogue. The price in 1925 for your gun as a 12G ejector was 14 pounds 14 shillings .The engraved version was 2 pounds 2 shillings extra.[ie priced in gns ,London fashion!]
B.S.A. states that the barrels are Jessops[A B.S.A.subsidiary] steel, made in Sheffield. They also claim that all parts are viewed and gauged at each stage of manufacture to ensure complete interchangeability.

Roy Hebbes