Too many choices Carpetsahib, might come down to what will work through you magazine!
6.5x54mm - 76mm OAL
7x57mm - 78mm OAL
7x54mm Lapua (6.5x55 base) - says 67mm OAL, I'd more believe closer to 80mm OAL!
7.5x55 Swiss - 78 OAL

https://en.wikipedia.org/wiki/7%C3%9754mm_Finnish