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Originally posted by Don Shearer:
Fireball,

It is quite right that we see lower velocities from pistol length barrels. But when it comes to critical values for twist rate, velocity is not in the equation. The determination of required twist rate to stabilize a bullet is pretty well handled by the Greenhill formula. Now that is a formula that was developed at turn of the century 1800-1900. That was when a bullet was a chunk of solid lead and had a round nose at best and was traveling at much slower velocities than we see today. That formula still is used, and sometimes it is necessary to tweek with a constant in the formula to get it to give the right answers for twist rate - especially if you are working with a hollow point or a plastic tipped bullet (that has a different balance set up than a solid bullet). The contolling factor is the bullet shape and its profile (or length) and center of balance that determines the twist rate needed to stabilize it.

It is also true that longer bullets require a faster twist than a short ones and most pistol shooters tend to want smaller bullets - thus the slower twist in pistol length barrels. But yes, if you want to shoot big bullets you will generally need a faster twist. But if you have a slow twist barrel and want to shoot big bullets, try what Don Bower does. Use lots of real slow powder. He seems to make that work. He shoots big bullets from 30 caliber barrels with twist as slow as 14" and makes them hit little targets at very long range too.

That sort of rambles on and on.

Don Shearer

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