TexasChase I got the following is from Wikipedia. It pretty much sums up what I have learned over the years about the 8X60 and does a much better job of explaining it than I could.
After World War I, the Allied forces signed the Treaty of Versailles. This Treaty prohibited the use of standard military weapons and ammunition by Germany. However, civilian hunters didn't want to give up on this great round, so a new cartridge was designed by the German arms manufacturer Deutsche Waffen und Munitionsfabriken (DWM). Extending the 7.92x57mm Mauser cartridge case by 3 mm (2 mm of lengthened body plus 1 mm of lengthened neck) created the 8x60mm S. The 8x60mm S bullet diameter is 8.20 mm (.323 in) as found in the 8x57mm IS.
The new cartridge used the same bullet and therefore only the chamber of the rifle had to be modified (reamed out by 2 mm plus 1 mm of neck extension) to accommodate the slightly longer case. This operation was easily performed on Gewehr 98 and Karabiner 98k rifles.
