8×64mm S

The 8x64mm S (also unofficially known as the 8x64mm 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. As is customary in European cartridges the 8 denotes the 8 mm bullet caliber and the 64 denotes the 64 mm (2.52 in) case length. The 8x64mm is a hunting cartridge in central Europe and can due to its 87.5 mm (3.445 in) overall length fairly easily be chambered in standard sized Mauser 98 bolt action rifles.

History
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.

In 1912 Brenneke designed the 8x64mm S cartridge. This cartridge is an example of a de novo rifle cartridge (the 8x64mm S and 6.5x64mm have no other cartridge as parent case) intended as a ballistic upgrade option for the Mauser Gewehr 98 rifles that were then standard issue in the German military. The exteriour cartridge case dimensions like overall length and slightly larger case head diameter compared to the German 8x57mm IS military cartridge coupled with a moderate increase in maximum pressure were chosen with easy conversion of Gewehr 98 rifles for the 8x64mm 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 German military chose however to stick to their 8x57mm IS rifle cartridge avoiding rechambering their service rifles for a larger and heavier cartridge that due to its more favourable bore area to case volume ratio ballistically slightly outperforms the .30-06 Springfield cartridge introduced by the United States Army in 1906.

Commercially the 8x64mm S was after an initial success phase in the period between the World Wars rather unsuccessful. Brenneke’s engineering concept to lengthen the 57 mm (2.244 in) long M/88 cartridge case to create new for those days very powerful cartridges was essentially sound and he persisted in the development of new cartridges like the commercially successful 7x64mm along this line.

The 8x64mm S offered compared to the 8x57mm IS about 2 to 5% extra muzzle velocity. This results in a flatter trajectory and better performance at longer range.

Beside the 8x64mm S rifle cartridge Brenneke also designed a rimmed version for break action rifles of the cartridge. The rimmed 8x65 mm RS variant of the cartridge was also rather commercially unsuccessful.

8x64mm
This cartridge also exists in a 8x64mm variant (without the S or any other further additions) intended for a different bullet diameter. Rifles chambered for the 8x64mm sport the earlier tighter 8.07 mm (.318 in) I-bore as found in the 8x57mm I.

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.

Cartridge dimensions
The 8x64mm S has 4.51 ml (69.5 grains) H2O cartridge case capacity. A sign of the era in which the 8x64mm S was developed are the gently sloped shoulders. The exterior shape of the case was designed to promote reliable case feeding and extraction in bolt-action rifles, under extreme conditions.



8x64mm S maximum C.I.P. cartridge dimensions. All sizes in millimeters (mm).

Americans would define the shoulder angle at alpha/2 ≈ 14 degrees. The common rifling twist rate for this cartridge is 240 mm (1 in 9.45 in), 4 grooves, Ø lands = 7.89 mm, Ø grooves = 8.20 mm, land width = 4.40 mm and the primer type is large rifle or large rifle magnum depending on the load.

According to the official with C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) guidelines the 8x64mm S case can handle up to 405 MPa (58740 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers.

The American 8mm-06 wildcat cartridge (in European nomenclature the 8mm-06 would be termed as 8x63mm S) is probably the closest ballistic twin of the 8x64mm S. This is a necked up .30-06 Springfield wildcat made to accept 8 mm (.323 in) bullets. This modification was performed to German Mauser 98 rifles in the US to facilitate the use of a commonly available cartridge case in the US, since the German 8x57mm IS cartridge was not readily available in the US when troops brought German Mauser rifles home as war souvenirs after World War II.

Contemporary use
The 8x64mm S is offered as a chambering option in some European hunting rifle manufacturer’s products palette. The 8x64mm S performance lies between the commercially important 8x57mm IS standard cartridge and the 8x68mm S magnum cartridge making it suitable for hunting all kinds of European game. In the year 2001 the Brenneke Company tried to revive the 8x64mm S cartridge by offering it loaded with 12.8 gram Brenneke Torpedo Ideal Geschoß (TIG) hunting bullets. Sellier & Bellot and Brenneke are currently (2007) the only ammunition manufacturers offering 8x64mm S factory loads. Loaded with short light bullets it can be used on small European game like roe deer and chamois. Loaded with long heavy bullets it can be used on big European game like boar, red deer, moose and brown bear. The 8x64mm 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 8x64mm S can be used in countries which ban civil use of former or current military ammunition. In France where the possession of rifles in their original military caliber is tightly regulated cartridges like the 8×64mm S allow French licensed gun owners to possess rifles based on the Mauser Gewehr 98 system under the less constraining "hunting rifle" category. The also rare 8x60mm S cartridge offers a comparable rechambering option for Mauser Gewehr 98 and Karabiner 98k based hunting rifles sporting 8 mm S-bores. Due to its larger case capacity the 8x64mm S chambering offers better ballistic performance than the 8x60mm S. The 8x64mm S rimmed sister cartridge, the 8x65mm RS, is also not popular in central Europe for the same reasons as the 8x64mm S.

8 mm cartridges compared
Maximum muzzle velocity comparison in % of the probably most proliferated European and American 8 mm rifle cartridges out of 650 mm (25.59 in) long barrels loaded with relatively light to heavy 8 mm bullets to their C.I.P. or SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) sanctioned maximum pressures.

This comparison is not totally objective since the 8 mm Remington Magnum operates at 460 MPa (66717 psi, the .325 Winchester Short Magnum at 435 MPa (63,091 psi), the 8 x 68 S at 440 MPa (63817 psi), the 8 x 64 S at 405 MPa (58740 psi) and the 7.92 x 57 mm Mauser at 390 MPa (56564 psi) maximum chamber piezo pressure. Higher chamber pressure results in higher muzzle velocities.