The reason why professional and military personnel decided to go with a slower twist is due to gyroscopic drift and the Magnus effect. When a body spins on itself, it creates a whirlpool of air making the bullet drift to the same side of the spin. Also, on right twist, the bullet will drop more and on left twist the bullet will rise a bit (the Magnus effect).
All this comes into play at long distances.
The bottom line is that you want enough twist for gyroscopic stabilization but not too much as not to enhance those side effects, hence the 12 twist because they do not shoot heavy bullets.
Decide on the bullet first, then get the appropriate rifling.
Last edited by nicknitro71; October 1, 2012 at 06:48 AM.