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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.
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.
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).
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.
In December 1955, Guns Magazine writer, H. Jay Erfurth in an article titled Two Varmint-Big Game Rifles discussing the .244 Remington and .243 Winchester wrote "the Winchester bullet of 100 grains is the better one for deer and medium game than the 90-grain Remington pointed soft-point, though the differences seem mostly splitting hairs." He ...
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]
Barrels were supplied by Rock Creek Barrel Inc. Various twist rates were tried with 5R rifling. It was designed as a way to optimize shooting the 19.44 grams (300.0 grains) 8.59 millimetres (0.338 in) caliber Sierra HPBT MatchKing projectile from actions and magazines that lack the length to handle cartridges exceeding 91.44 mm (3.600 in) in ...
Care must be taken to confirm what twist rate was used, as the earlier West German 7mm Weatherbys used a 1-in-12 twist vs the faster 1-in-10 twist for those of later manufacture. The 1x12 twist rifles will not stabilize bullets over 150 grains, while the 1x10 twist rifles will stabilize bullets weighing up to 175 grains.