rifle twist, ball vs bullet

[Mad_Dog]

How does the rifle twist affect accuracy with a light vs heavy projectile (round-ball vs bullet, for instance)?  I've read that it affects it, but it's not entirely clear to me what the relation is...

-Mad Dog

[Sir Charles deMouton-Black]

Greenhill and his formula;

http://en.wikipedia.org/wiki/Alfred_George_Greenhill

The calculator;

http://www.z-hat.com/twistrate.htm

[StrawHat]

In a nutshell, the longer the bullet, the tighter the twist for the caliber.  A roundball from a muzzle loader can have a twist longer than 1 turn n 100 inches and still show reasonable accuracy and great velocity.  A 500 grain bullet in a 45 caliber bore wants something about 1 turn in 22 inches or a bit tighter.