The Greenhil formula calculates the twist rate required to stabilize a bullet of a given length. Longer bullets require faster twist rates to stabilize for a given bore size. What Greenhill doesn't seem to address is bullet velocity. A bullet with a muzzle velocity of 3000fps will be spinning twice as fast as the same bullet with a muzzle velocity of 1500fps if they are fired from the same barrel. Is there a specific velocity that Greenhill was developed for, or am I misunderstanding this?
The reason for this rather rambling question is that I am experimenting with paper patched bullets in a 270 Winchester. I am using cast 6.5mm bullets and the bullet I like best (Lyman 266469 140 gr. Loverin style) is just over the theoretical length that can be stabilized by my 1 in 10 twist in my 270 according to Greenhill. Some of the shots on target are good round holes, but some are obviously tumbling. Can I shoot the same bullet at a higher velocity and maybe get it to stabilize better, or am I just chasing something that won't work with my twist rate?
