I ran across this pic of a BSA Lee-Speed and I believe it may be the same as the No. 1 Pattern in 375 caliber as shown on the catalog page I posted earlier. The image origin did not mention anything about calibers so can't be positive. However, looking at the mag box shape and stick out from the bottom it certainly isn't a 10 shot or a 5 shot mag. Won't be able to positively identify until I find out ore info on this in my google searching.