....The Greenhill formula goes like this: 150 divided by the bullet length in CALIBERS equals the required twist rate in CALIBERS.
Let's say you have a .224, 75 gr. bullet 4.5 calibers long (1.008").
150 divided by 4.5= 33.33. So, the rate of twist needs to be one turn in 33.33 CALIBERS. Your caliber is .224, so 33.33 x .224= 1 turn in 7.46". In this example, the bullet MIGHT be stabilized in a 1 in 8" twist, but should definitely stabilize in a 1 in 7" twist. MV does help some in stabilizing bullets fired in a too-slow twist. It's better to have a bullet spinning too fast or "overstabilized" than too slow.