Most interesting on the Modell 88/8mm stamp there Axel. I was curious when the stamp saw its last use. And was the 15 gram bullet more common for the IR, IRS or both?
Apparently the changeover was completed 1926. Jon Speed's book "Original Oberndorf Sporting Rifles", page 274, shows a table of cartridge dimensions agreed upon July 23, 1926 by the German arms and ammo manufacturers association. It shows new//old designations: 8x57IR // M88/8 mit Rand or M88B, 8x57I // M88N, 8x51 // M88/8 kurz or H, 8x57IS // M88/8S.
The German M1888 cartridge was loaded with a .318" 14.7gramm = 227grs (roughly 15gramm)round nose bullet. This was the standard/only hunting load up to WW1. The military S cartridge used a .323" 10g = 154gr pointed bullet that never became popular as a sporting load. In WW1 the German army changed to the sS = heavy pointed bullet for machine gun use, bullet weight 12,7g =196gr. This became the standard weight for both the I and S bores close to WW2. Up until after WW2 the I = .318" bullet was regarded as the sporting type, while the S-bore was the "military" one, used on Sporting rifles mostly for the "Magnum" loads to relieve pressures. Only the 1940 proof law introduced min-max dimensions and the strict differentiating between I and S bores. So take any rifle proofed for a 15g bullet to be an I bore. Also, any other commercial pre-WW2 8mm barrel, except you prooved otherwise by slugging the bore and making a chamber cast.
