How is twist rate calculated?
Divide the specific gravity, SG of the bullet by 10.9. Find the square root of the resultant. Multiply the resultant with constant C , 150, and the square of the projectile diameter, D . Divide the product by the length of the projectile L to get the twist rate in inches per turn, t .
What twist rate do I need?
The 1:8 twist barrel is the most versatile of the bunch. This twist rate gives you the most flexibility, effectively stabilizing projectiles up to 80 grains but not over stabilizing lighter ammunition. The 1:9 barrel is best for stabilizing lighter and mid-weight bullets ranging between 45 and 77 grains.
What is the Greenhill formula?
Enter Professor Sir Alfred George Greenhill of the British Royal Military Academy, who devised a formula for determining twist rate which, simplified here, multiplies the square of the bullet diameter by 150 and then divides the result by the length of the bullet, and looks like this: (C x D2) ÷ L = T.
What are 1/10 twists good for?
It’s important that your barrel has an adequate twist rate to stabilize the bullets you’re shooting. A barrel that is a 1:10” twist means that the rifling will spin the bullet one revolution in 10 inches. The lower the number of the twist, the faster the twist rate or the faster the bullet will spin.
What grain bullet is best for 1 in 11 twist?
bullets with a 1 in 11 twist. You’ll most likely find satisfaction when running bullets weighing 165gr. to 180gr.
What is the best twist rate for 6.5 Creedmoor?
1–8” twist
The Creedmoor was designed with a 1–8” twist, which allows the use of the heaviest bullets available in 6.5 mm. What was the caliber specifically designed for? We originally envisioned it as a target/match cartridge that would have good longer range performance.
What RPM does a bullet spin?
Bullet spin A bullet fired from a rifled barrel can spin at over 300,000 rpm (5 kHz), depending on the bullet’s muzzle velocity and the barrel’s twist rate.
Is a 1/7 twist barrel good?
Give 1:7 a try. Both are extremely common, and I have little doubt you’ll find what you need for most uses. As a general rule, you can get away with a faster spin rate than necessary for a specific bullet, but twist a bullet too slowly and you’ll lose some of your accuracy and stability.
What is the most accurate barrel length for 6.5 Creedmoor?
As with most rifle cartridges, the best velocities are typically obtained out of longer 24 to 26-inch barrels. Greater velocity provides flatter trajectories and less wind deflection with all else being equal.
What grain bullet is best for 1 in 12 twist?
The 1:12 is perfect for lightweight 55-grain bullets, which constitute the majority of practice and plinking . 223 ammunition. However, most modern carbine barrels shorter than 20 inches feature faster twist rates, so shooters wanting a 1:12 should stick to the old-school 20-inch rifle pipe.
Does a dirty barrel affect accuracy?
This bore insists on a certain amount of buildup to group tightly. This is really quite unusual; copper fouling is the enemy of accuracy and for a rifle to shoot its best it has to have a clean bore, but there always seems to be an exception.