The information below will help you select the best barrel twist for your specific needs, providing of course there are multiple choices. If you'll be shooting one bullet weight, choose a twist from the chart just fast enough to stabilize it. Too fast a twist simply overspins the bullet and may result in reduced accuracy. So if you're going to be using several bullet weights, be sure to select a twist that will stabilize the heaviest one, since lighter bullets will also be stabilized.
By way of explanation, the numbers in the Twists column indicate how far the bullet must travel through the bore to make one full revolution. This is determined by the rate of rotation of the rifling. For example, a 9" twist barrel spins the bullet one full turn when it travels 9 inches through the bore. In a 16" twist barrel, the bullet makes on revolution in 16 inches. So at the same bullet velocity, the 9" twist is faster (spins the bullet faster) than the 16" twist. Consequently, as the chart reflects in the .224 CF section, the 9" twist is necessary for stabilizing heavier bullet weights.
Again looking at the .224 CF section, if you're planning to shoot 55-grain bullets, the 14" twist is ideal. This twist is also the best choice for 52-and 53-grain match bullets driven at moderate velocities. But if you're also contemplating shooting a 60-grainer, go with the 12" twist, since it will stabilize all the bullets you'll be using. As you can see from the 15" and 16" twists, higher velocities also spin the bullet faster and my enable a slower-than-recommended twist to stabilize a marginally overweight bullet.
As a general rule: The higher the velocity, the slower twist is required. The lower the velocity, the faster twist is required.