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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.
Rifling of a 105 mm Royal Ordnance L7 tank gun Conventional rifling of a 90 mm M75 cannon (production year 1891, Austria-Hungary) Rifling in a GAU-8 autocannon. Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy.
Another issue that has an effect on the barrel's hold on the bullet is the rifling. When the bullet is fired, it is forced into the rifling, which cuts or "engraves" the surface of the bullet. If the rifling is a constant twist, then the rifling rides in the grooves engraved in the bullet, and everything is secure and sealed.
SAAMI recommends a six groove barrel with a rate of twist of one revolution in 9 in (230 mm), a bore diameter of .256 in (6.5 mm) and a groove diameter of .264 in (6.7 mm) with each groove having a width of 0.090 in (2.3 mm). The recommended maximum pressure for the cartridge (piezo) is 64,000 psi (4,400 bar).
They are considered very collectible as only 250 of each caliber were made. There is a unique barrel stamping on these rifles which is denoted as Marlin 1894 LTDSS, followed by the caliber; example "Marlin 1894LTDSS 41 Magnum". These rifles were chambered in .357 Magnum/.38 Special, .41 Magnum/.41 Special, .44 Magnum/.44 Special, and .45 Long Colt.
SAAMI and the CIP recommend a 6-groove barrel with a twist rate of one revolution in 10 in (250 mm) of barrel length with a bore Ø of .330 in (8.4 mm) and a groove diameter of Ø of .338 in (8.6 mm), with each groove having a width of .110 in (2.8 mm). The SAAMI-recommended average pressure for the cartridge is 64,000 psi (4,400 bar).
Common rifling twist rates also often have to be tightened to stabilize very long projectiles. Such commercially nonexistent cartridges are termed "wildcats". The use of a wildcat-based (ultra) long-range cartridge demands the use of a custom or customized rifle with an appropriately cut chamber and a fast-twist bore.
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.