6.5x68mm

The 6.5x68mm rimless bottlenecked rifle cartridge (also incorrectly known as the 6.5x68mm RWS, 6.5x68mm Schüler or the 6.5x68mm Von Hofe Express) and its sister cartridge the 8x68mm S were developed in the 1930s by Mr. Schüler from the August Schüler Waffenfabrik, Suhl, Germany as magnum hunting cartridges that would just fit and function in standard sized Mauser 98 bolt action rifles. This is one of the early examples where a de novo rifle cartridge (the 6.5x68mm and 8x68mm S have no other cartridge as parent case) was developed by a gunsmith to fit a specific popular and widespread type of rifle.

History
The German ammunition manufacturer RWS (Rheinisch-Westfälischen Sprengstoff factories) introduced both cartridges commercially in the spring of 1939. With the official certification of the .375 Hölderlin this German 68 mm "family" of magnum rifle cartridges that all share the same basic cartridge case got expanded 68 years later.

The cartridges in this German 68 mm cartridge "family" are, in the order of development:
 * 8x68mm S (1939)
 * 6.5x68mm (1939)
 * .375 Hölderlin (2007)

Standard military 7.92x57 mm Mauser 98(k) rifles have to be adapted by a competent gunsmith to function properly with these magnum cartridges since they are longer and the cases have a larger diameter then 7.92x57mm Mauser cartridges. The 7.92x57mm Mauser cartridge is also known as the 8 mm Mauser or in Germany as the 8x57mm IS (IS stands for Infantrie Spitz). In adapted standard military Mauser 98k rifles the large 6.5x68mm cartridges are however praised for very smooth and reliable feeding.

The widespread availability of standard size Mauser 98 rifles and the fact that the .375 H&H Magnum cartridge and its necked down version the .300 H&H Magnum with approximately 72.4 mm case length were too long to fit in standard sized Mauser 98 bolt action rifles makes the shorter 6.5x68mm, 8x68mm S and .375 Hölderlin interesting chambering options.

World War II spoiled the commercial introduction and spread of the 6.5x68mm. The cartridge became popular after World War II due to its high performance and flat trajectory, when German hunters were allowed again to own and hunt with full bore rifles. The 6.5x68mm's performance also made it that hunters who had problems with handling magnum cartridge recoil stepped down to less powerful but adequate medium cartridges like the 6.5x57mm 7.92x57 mm Mauser, 7x64mm (Brenneke) or .30-06 Springfield (also know as the 7.62x63mm in metric countries). Recoil sensitive shooters can fit an efficient muzzle brake to significantly reduce the amount of recoil. With the help of a muzzle brake, the 6.5x68mm's recoil is reduced to tolerable levels.

Cartridge dimensions
Extremely thick brass results in 'only' 5.58 ml (86 grains) H2O cartridge case capacity for the 6.5x68mm. A rare feature of this German rimless bottlenecked centerfire cartridge design is that it has a slightly rebated rim (P1-R1 = 0.3 mm). A sign of the era in which the 6.5x68mm 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.



6.5x68mm maximum C.I.P. cartridge dimensions. All sizes in millimetres (mm).

Americans would define the shoulder angle at alpha/2 ≈ 14.53 degrees. The common rifling twist rate for this cartridge is 250 mm (1 in 9.84 in), 4 grooves, Ø lands = 6.45 mm, Ø grooves = 6.70 mm, land width = 3.50 mm and the primer type is large rifle magnum.

According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) guidelines the 6.5x68mm case can handle up to 440 MPa (63817 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.

When the 6.5x68mm was introduced in 1939 it probably held the title of fastest production cartridge on the market. Nowadays there are commercial cartridges on the market which offer even higher muzzle velocities.

The American .264 Winchester Magnum cartridge introduced in 1959 and the French 6.5x63mm Messner Magnum are probably the closest ballistic twins of the 6.5x68mm.

The 6.5x68mm in field use
German and Austrian hunters use the powerful, high velocity 6.5x68mm for long-range hunting in mountainous terrain like the Alps mountain range. The 6.5x68mm as a pure civil cartridge can be used in countries which ban civil use of former or current military ammunition.

Since there are not many factory loads available (RWS offers only 2 factory loads) and due to its good field reputation, the 6.5 x 68 is often used by reloaders. They have used this cartridge extensively to create powerful loads by handloading.

Factory rifles in 6.5x68mm normally have 250 mm to 280 mm (1 in 9.8 to 11 inch) twist rates, which are too long to adequately stabilize modern long heavy 6.5 mm bullets. This slow twist rate was chosen since the bullet jackets used in the 1930s were not strong enough to cope with the forces generated by the magnum muzzle velocities of the 6.5x68mm. The traditional 6.5x68mm twists nowadays inhibits its potential. To make the 6.5x68mm an awesome long-range cartridge, rifle barrels with a 200 mm to 230 mm (1 in 7.9 to 9 inch) twist rate are a better choice. Due to the large case capacity in relation to the 6.5 mm (.264 inch) caliber bore size the 6.5x68mm is very harsh on barrels. The 6.5x68mm typically wears out a rifle barrel in 500 to 1000 rounds. A lot of thorough barrel cleaning (after every 5 shots) and carefully avoiding long strings of shots help to minimize barrel wear. This makes this cartridge unpractical for most competition shooters who tend to fire a lot of rounds in practice to acquire and maintain expert long-range marksmanship.

Reloaders use the 6.5x68mm as a Jack of all trades long-range cartridge on all European game from fox, roe deer and chamois upwards to the big European game like red deer and moose. These people realized that bullets with different characteristics can be utilized to produce varying effects on game. As with all 6.5 mm cartridges, the big game hunting bullets used in the 6.5x68mm have comparatively high sectional densities for good penetration on suitable size game animals.

The 6.5x68mm as parent case
Cartridges that are not officially registered with nor sanctioned by C.I.P. (Commission Internationale Permanente Pour L'Epreuve Des Armes A Feu Portative) or its American equivalent, SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) are generally known as wildcats. By blowing out standard factory cases the wildcatter generally hopes to gain extra muzzle velocity by increasing the case capacity of the factory parent cartridge case by a few percent. Practically there can be some muzzle velocity gained by this method, but the measured results between parent cartridges and their 'improved' wildcat offspring is often marginal. Besides changing the shape and internal volume of the parent cartridge case, wildcatters also can change the original caliber. A reason to change the original caliber can be to comply with a minimal permitted caliber or bullet weight for the legal hunting of certain species of game.

Wildcats are not governed by C.I.P. or SAAMI rules so wildcatters can capitalize the achievable high operating pressures. It is often reported that modern 68 mm RWS brass can tolerate up to 500 MPa (72519 psi) piezo pressure. Because the 6.5x68mm offers an exceptional sturdy, pressure resistant cartridge case that can relatively easily be reloaded with primers, powder and bullets and hence be reused several times it has become quite popular amongst wildcatters. With the German 68 mm magnum cartridge case as parent case wildcatters have created .25x68, .270x68, 7x68mm, .30x68, .338x68, .375x68 or .416x68 variants.

Categories
Cartridge:rifles