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Thus the optimum rate of twist for this bullet should be approximately 12 inches per turn. The typical twist of .30-06 caliber rifle barrels is 10 inches per turn, accommodating heavier bullets than in this example. A different twist rate often helps explain why some bullets work better in certain rifles when fired under similar conditions.
Norway adopted the Krag–Jørgensen M/1894 rifle, while Sweden adopted the Mauser m/1896 rifle design that was based on a Mauser service rifle designed around the 7×57mm Mauser cartridge. The 6.5×55mm cartridge has a smaller bullet diameter and lower free recoil than other full-power service rifle cartridges like the .303 British , 7.92× ...
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. This means that 8mm Remington Magnum chambered arms in C.I.P. regulated countries are currently (2014) proof tested at 550.00 MPa (79,771 psi) PE piezo pressure.
Most factory Swift rifles come with a fairly slow twist-rate such as 1–12 or 1–14 inch, designed to stabilize the lighter bullets popular in varmint hunting. Custom Swifts can have faster twist-rates such as 1–9 inch allowing them to stabilize heavy bullets, including those with a construction suitable for larger game. [15] [16]
The recommended optional twist rate is one revolution in 10 in (250 mm). Both SAAMI and Weatherby recommend a freebore of .378 in (9.6 mm). Early .257 Weatherby rifles has a twist rate of 1 revolution in 12 in (300 mm) but all current rifles are manufactured with a twist rate of 1 revolution in 10 in (250 mm).
To obtain maximum accuracy, bullet weight and form are matched to the rifling twist rate of the barrel. Typically, 68 gr (4.41 g) bullets are used in barrels with twist rates of 1 in 13 inch (1 in 330 mm), while 1 in 15 inch (1 in 380 mm) barrel twists can accommodate lighter 58 or 60 gr (3.76 or 3.89 g) accurately.
The common rifling twist rate for this cartridge is 305 mm (1 in 12 in), 4 grooves, Ø lands = 7.62 mm, ... (1 in 10 in) twist rate is also commonly applied.
When comparing the .300 RUM and the .300 Weatherby Magnum, however, there is a difference in factory loadings. Performance data is often listed on the side of the ammunition box for those who wish to do an in-store comparison. On average, Weatherby factory ammo is loaded to higher chamber pressures than Remington or Winchester magnum rounds.