Actually it is nice to know the velocity range.The 1 in 12" usually works very well for the 308win and other lower velocity cartridgesbut the 300 magnums seem to do better with a 1 in 10" twist.

I like the 1 in 10" twist for my 7mmstws and for the 7mmremmag,but some people prefer a 1 in 9" twist.

Too slow a twist can result in the heavier bullets not stabilizing properly and a tighter than required twistcan reduce the velocity potential slightly.Lazzeroni uses a slower rate of twist claiming that it provides more velocity with equal pressure.There is one more alternative which is the gain twist rifling where the twist rate actually changes in the barrel.Gain twist barrels are said to provide more velocity with equivalent pressure.