It was not the 8x54R, but rather the Austrian 8x50R Mannlicher cartridge, aka .500/320 Flanged, as well as the 7x57.

I also have an Alex. Martin commercial B.S.A.Co. C.L.L.E. sporting rifle (post Speed patents) in .256 Mannlicher, aka 6.5x53R, .256 Swift Flanged & .256 Fraser Flanged.