Rifling Twist Calculator
This calculator operates by the Greenhill Formula. The Formula for this calculator is setup for Copper Jacketed Lead Core Bullets. http://www.tanksrifleshop.com/twistcalc.htm

I don't understand. What is it supposed to tell you? Wouldn't the bullet twist be the same as the barrel twist? Here are the values I put in and I come up with a bullet twist of 1 in 3. Rifling Twist Calculator This calculator operates by the Greenhill Formula. The Formula for this calculator is setup for Copper Jacketed Lead Core Bullets Only. Caliber (.xxx"): .223 Bullet Length: 2.48" Velocity Value1: 160 Bullet Twist: 1- 3"

Supposed to give the correct twist for the bullet you enter. I ran some .264 and it came out 1-13. Seems like the weight would be a factor Maybe this will explain it. T = required twist IN CALIBERS T = 150 divided by the length of the bullet IN CALIBERS To figure out what twist you need, disregard weight, and just measure the length of the bullet in inches. Divide this measurement by the diameter of the bullet in inches. Next divide 150 by this new figure. Now convert the result back to into inches, and you'll have the result that tells you how many inches are allowed in which the bullet must make one complete revolution. (See page 556 in Hatcher's Notebook.) Example: A .30 caliber 220-grain bullet is 1.35 inches long, divided by .30 = 4.5 This bullet is 4.5 CALIBERS long. Next, required twist = 150/4.5, or 33.33 CALIBERS. 33.33 CALIBERS - 9.99" . So a .30 cal bullet, 1.35" long, of whatever weight can be stabilized by a 1 in 10" twist.