Just measured the inside lengths of M-S 1903, 1905 and 1910 magazines. They are all 78.0 mm, rear to front wall. I have no 1908, but guess it's the same. The cartridges need a bit of clearance to prevent binding. So the maximum cartridge oal is about 77 mm, or a wee bit over 3". My own 9.5x57 M-S loads with a 235 gr Barnes TSX bullet are 77.2 mm, absolute maximum imho.