The 8×64mm S (also unofficially known as the 8×64mm S Brenneke) (the S means it is intended for 8.2 mm (.323 in) groove diameter bullets) is a rimless bottlenecked centerfire cartridge developed as a military service round for the German Army who never issued it.
The 8×64mm is a hunting cartridge in central Europe and can due to its 87.5 mm (3.445 in) maximal overall length fairly easily be chambered in standard sized military Mauser Gewehr 98 bolt-action rifles.
At the start of the 20th century the famous German gun and ammunition designer Wilhelm Brenneke (1865–1951) was experimenting with the engineering concept of lengthening and other dimensional changes regarding standard cartridge cases like the M/88 cartridge case, then used by the German military in their Mauser 98 rifles, to obtain extra muzzle velocity.
The external cartridge case dimensions like overall length and slightly larger case head diameter compared to the German 8×57mm IS military cartridge coupled with a moderate increase in maximum pressure were chosen with easy conversion of Gewehr 98 rifles for the 8×64mm S in mind.
Brenneke hoped that he could achieve a major success with this round designed in an age when military doctrine expected rifle shots at ranges up to 800 to 1000 m (875 to 1094 yards).
The gun designer Otakar Galaš originally developed a sniper rifle based on a Mauser M98 action chambered in 8×64mm S around 1950.
To avoid potentially serious accidents, it is important to distinguish clearly between cartridges loaded for these two different bullet diameters, and only fire them in appropriately chambered/barrelled rifles.
(Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) rulings the 8×64mm S can handle up to 405.00 MPa (58,740 psi) Pmax piezo pressure.
Loaded with long heavy bullets it can be used on big European game like boar, red deer, moose and brown bear.
The 8×64mm S offers very good penetrating ability due to a fast twist rate that enables it to fire long, heavy bullets with a high sectional density.
The also rare 8×60mm S cartridge offers a comparable rechambering option for Mauser Gewehr 98 and Karabiner 98k based hunting rifles sporting 8 mm S-bores.