Re: what barrel length and contour for a 300win mag long range rifle
Need to tell us more about the build you want.
The contour depends on the weight you want the rifle to come it at. For example a "Sendero" contour barrel will generally put you in the 10lb range with optics and such. You can adjust contour from there.
You won't go wrong with a 10 twist, as it will handle the 180-210 grain pills.