Ghostrider,
The 8x57IR case and 8x57IRS case are the same, except for the headstamp and neck diameter. When you fire one of the cartridges, if a .323" bullet slips easily into the case neck, you can load .323" bullets. If that is the case, it just means the neck diameter in the chamber is large enough to release a .323" bullet. If a .323" bullet won't go in, but a .321" bullet will, you can use that diameter. It really as bad as it seems. In the early days before WW1, the Germans discovered they could safely 8x57S ammo in M88 rifles that had chamber necks large enough, and conversion amounted to replacing the sights to match the new trajectory. The German military inspected the M88 rifles in their inventory and opened up the necks of those that needed it and changed the sights. This doesn't apply to the M88s held by their allies nor to commercial versions, so each rifle should be checked before using "S" ammo. Incidentally proof cartridges for 8x57J and 8x57S rifles were loaded to the same pressure, so it is not correct that M88 rifles were weak. After WW1, treaty restrictions prohibited making new 8x57S arms, but the Mauser company made their chamber necks large enough for "S" bullets in .318" groove diameter barrels. This doesn't apply to other companies, so you can't presume "S" ammo is safe without checking.
Mike
