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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.
The 7.92×33mm Kurz has a 2.22 ml (34.3 grain H 2 O) cartridge case capacity.. 7.92×33mm Kurz maximum C.I.P. cartridge dimensions.All sizes in millimeters (mm). Americans define the shoulder angle at alpha/2 ≈ 17.5 degrees. The common rifling twist rate for this cartridge is 240 mm (1 in 9.45 in), four grooves, Ø lands = 7.89 millimetres (0.311 in), Ø grooves = 8.20 millimetres (0.323 in ...
Bullets in this caliber are hard to find but provide greater weight than .223 caliber bullets, up to 100 grains (6.5 g), without excessively quick twist rate. The .257 Roberts Ackley Improved is a second generation wildcat cartridge based on the .257 Roberts cartridge.
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).
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.
The twist rate for the 7x64 is 1 in 8.66 inch against 1 in 10 inch for the 280 Remington. Nearly every European rifle producer offers the 7x64 as a standard caliber. The .280 Remington does, however, have a larger than expected number of European users in imported self-loading rifles such as those by Remington.
SAAMI recommends a barrel with a 6 groove contour and a twist rate of one revolution every 9 in (229 mm) with each groove having a width of .095 in (2.41 mm). The recommended bore diameter is .256 in (6.50 mm) and the groove diameter is .264 in (6.71 mm). SAAMI recommends that rifling commence at .221 in (5.61 mm) from the chamber mouth.
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.