Bullet grain v. Barrel twist

[Rocky Raab]

There are several formulas out there, the most commonly known being the Greenhill Formula.

In practice, they work acceptably, but aren't completely accurate because they don't take bullet shape into account.

However, twist rate is determined not by bullet weight, but by its length. The longer the bullet, the faster it has to be spun to stabilize it. The shorter (or blunter) the bullet, the slower the twist rate needed.

What are you trying to determine? I can plug in some numbers and calculate a workable twist rate. I need caliber, velocity and bullet length.