#8 Wrong guesses so far: 7.7 Jap, 7.7x58, 30 Rem, 7x57
Still on table are a 8x57, 6mm Lee navy and a 7x60 BSA guesses.
Seems I remember a wildcat 7mm.
That used a necked down reformed 8mm Mauser case.
Hence the shoulder was farther forward than the std 7x57
And thus it had more case capacity than a std 7x57.
So... My #8 guess is a 7/8mm Mauser wildcat
cause I can't remember a specific cartridge name for it.