The speed of the bullet and caliber will also influence the rate of twist. It will obviously take more spin to stabilize a long for caliber bullet like the 80 grain .22 cal bullets, than a shorter faster bullet like the 55 grain bullet in the same caliber. Traditionally, Gunsmiths have used the Greenhill Formula to determine the optimal twist for a particular bullet. The formula is T=150(d/r) for velocities from about 1500 to 2800 fps (substitute 180 for the 150 value for velocities exceeding 2800 fps). In the formula " T" is the twist rate. " d" is the bullet diameter. " r" is the bullet length to diameter ratio (length of bullet divided by diameter). So the total picture looks like this the three factors that influence twist are caliber, bullet length, and velocity.

Gordon