If you insist...
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. "T" is the twist rate. "d" is the bullet diameter. "r" is the bullet length to diameter ratio (length of bullet divided by diameter).
Or, just go here...
http://www.z-hat.com/twistrate.htm
Please note (AGAIN) that bullet weight has nothing to do with it.