hadmanysons

February 20, 2010, 12:57 AM

The first being that, when using the Greenhill formula to calcuate the optimum twist rate for a bullet, you divide 150 by the bullets (length/width) and then multiply by the width or 150 times the width squared, all divided by the bullet length.

Now, that will tell you the optimum twist rate for a bullet of that particular width and length but if you already know the twist rate and bullet width and want to find the optimum length bullet for that twist rate you just do 150*width squared divided by twist rate and it will tell you the length you need.

It's pretty hard to shop for a bullet based on it's length though since bullets are measured in width and weight. I know that using that formula, the optimum twist rate for a .308 168gr Sierra match king (which is approx 1.2 in long) is 11.858 inches. Now if I take 168/1.2 I get approx 140 grains of weigh per inch. So if I use my reverse formula and find out that the optimum bullet length for a barrel of 1 in 10" (which mine is) is 1.42296 inches and multiply that by the 140 grains per inch idea I get approx 199 grain bullet.

Am I right here? Is that a good way to judge what WEIGHT bullet is right for a barrel. What is more important to twist rate, bullet length or bullet weight? What I mean by that last question is, is the bullet stabilization more affected by an increase in bullet length or bullet weight?

*exhale*

Now, that will tell you the optimum twist rate for a bullet of that particular width and length but if you already know the twist rate and bullet width and want to find the optimum length bullet for that twist rate you just do 150*width squared divided by twist rate and it will tell you the length you need.

It's pretty hard to shop for a bullet based on it's length though since bullets are measured in width and weight. I know that using that formula, the optimum twist rate for a .308 168gr Sierra match king (which is approx 1.2 in long) is 11.858 inches. Now if I take 168/1.2 I get approx 140 grains of weigh per inch. So if I use my reverse formula and find out that the optimum bullet length for a barrel of 1 in 10" (which mine is) is 1.42296 inches and multiply that by the 140 grains per inch idea I get approx 199 grain bullet.

Am I right here? Is that a good way to judge what WEIGHT bullet is right for a barrel. What is more important to twist rate, bullet length or bullet weight? What I mean by that last question is, is the bullet stabilization more affected by an increase in bullet length or bullet weight?

*exhale*