Barrel twist rates for conventional rifling recommended by Shilen Barrels in this link:
http://www.shilen.com/calibersAndTwists.html
30 Caliber:
7" for heavy VLD bullets and/or subsonic ammo.
8" for bullets heavier than 220 gr.
10" for bullets up to 220 gr.
12" for bullets up to 170 gr.
14" for bullets up to 168gr.
15" for bullets up to 150 gr.
17" for bullets up to 125 gr.
22 Caliber:
7" for bullets up to 90 gr.
8" for bullets 80 gr. and under
9" for bullets up to 70 gr.
10" for bullets up to 65 gr.
12" for bullets up to 63 gr.
14" for bullets up to 55 gr.
Muzzle velocity must not matter.
http://www.shilen.com/calibersAndTwists.html
30 Caliber:
7" for heavy VLD bullets and/or subsonic ammo.
8" for bullets heavier than 220 gr.
10" for bullets up to 220 gr.
12" for bullets up to 170 gr.
14" for bullets up to 168gr.
15" for bullets up to 150 gr.
17" for bullets up to 125 gr.
22 Caliber:
7" for bullets up to 90 gr.
8" for bullets 80 gr. and under
9" for bullets up to 70 gr.
10" for bullets up to 65 gr.
12" for bullets up to 63 gr.
14" for bullets up to 55 gr.
Muzzle velocity must not matter.