The other day, I purchased a number of old military cartridges from a local collector, and as I’ve sorted through them I found I misidentified one initially. I thought it was an 8x50mmR Steyr cartridge, but the case measures ≈53mm in length. The bullet is a round nosed fmj, with what looks like a cupro-nickel jacket material? The overall length is ≈77mm. It was manufactured by Keller&Co. in 1891, as denoted by the headstamp: III 18 91 K.&C. The rim diameter and case shoulder look the same as an 8x50mmR Steyr. So I’m a little stumped. It’s not an 8mm Murata, but I’m not sure what it could be, other than some variation of the 8mm Steyr. I’ve included some pictures comparing it to a 1909 dated 8x50mm Lebel Balle M cartridge, and a 1937 dated 8x50mm Steyr. Any help would be appreciated!