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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.
The original 6.5×52mm barrel design, developed by the Brescia Arsenal at the same time as the cartridge before development of the M91 Carcano rifle itself, used a gain twist barrel with deep rifling to reduce wear and give consistent accuracy.
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.
To make the 6.5×68mm 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 6.5×68mm is very harsh on barrels. The 6.5×68mm typically wears out a rifle barrel in 500 to 1000 rounds.
6.5 Creedmoor with a 1:8 twist, 24 in (61 cm) barrel, weighing 10.6 lb (4.8 kg) .243 Winchester with a 1:7.7 twist, 26 in (66 cm) barrel, weighing 11 lb (5.0 kg) A newer Ruger Precision Rifle "Gen 2" was announced on 6 May 2016 with several enhancements over the original. [ 4 ]
A slight gain in the rifling twist, or a slight tapering down of the bore, will still ensure the tight fit of bullet to bore, so when selecting a barrel, the tighter or faster twist end should be chosen for the muzzle. [37] [38] [39] The twist of the rifling must match the intended ammunition for best accuracy.
Rifles chambered for this wildcat cartridge, with a cartridge overall length of 119 mm (4.685 in), were to have been equipped with custom made 762 mm (30 in) long 203 mm (1:8 in) twist rate barrels. [17]
Total length: 38.5 inches; Weight: 6.7 lbs; Barrel length: 20 inches; Twist: 1 turn in 10" Caliber: .30-30 Winchester; Magazine: tubular, seven round capacity (one in the chamber and six in the magazine) Finish: Blued Steel and Wood; Model 464: .22 Long Rifle Total length: 38.75 Inches; Weight: 5.6 lbs; Barrel length: 18 inches; Twist: 1 turn ...