http://www.imrpowder.com/basic-manual-inquiry.html
Take a look on this link. That should answer some of you questions. Get a couple of good manuels and read the text on reloading basics. Faster twists are necessary for longer heavier bullets when shooting heavy for caliber rounds. For the 25-06 your twist rate is good for everything from 75 gr up to 120 gr. bullets.