This .375 Flanged Nitro Express was introduced in 1899 and should not be confused with the Flanged Magnum of the same caliber which has a larger case. The cartridge was used in both single shot and double rifles and BSA made a bolt action rifle for this round as well. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.