Short summary of the history of the BSA pistol cartridges from Vol. 2 No.7 of The Historical Breechloading Firearm Association by Dr GL Sturgess.
Both German and English arms manufacturers suffered a significant decline in their fortunes after the end of WW1 with the cancellation of most, if not all their lucrative contracts. Many factories, including the Birmingham Small Arms Co. were left with no further orders and thousands of parts for guns that were no longer needed. A great number of companies faced bankruptcy, had to downsize considerably or look to diversify into other markets. As was the case after the Boer War in 1902, when the Company diversified into bicycles and motorcycles, BSA diversified again but into the resumption of air-guns as well as developments into shotgun and handgun designs with no previous experience in the design or manufacturing of either. They designed a line of pistol cartridges made by Eley, with a belted design in .28, .34 and .39 caliber and it is mentioned that the use of the belted case design for these radical new designs by BSA as well as the .26, .33 and .40 BSA rifle calibers together with the .250, .370 and .380 prototype designs by Cogswell & Harrison were as a result of the expiry of Holland’s 1904 patent BP27,912/1904 in 1918. The Cogswell & Harrison designs never got off the ground, while the BSA rifle calibers were short lived at best. The three pistol & Revolver cartridges are basically unheard of and extremely rare in collecting circles, while the actual BSA handguns are virtually unknown with very few specimens surviving. None were ever offered for sale in any BSA catalogue, there are no registered patents or internal company documents. (Erlmeier, Brandt Ref. 380)