I am hooked on Bartlein's Transitional (gain) twist barrels, with 5R lefthand rotation rifling. Take the twist rate you want, and start 1 revolution slower, transitioning faster to the muzzle, ending at the rate you desire. I have a 6.5 PRC with 1:8.5 to 1:7.5 5R LH that is working great. The gain twist is easier getting the projectile up to speed, especially good for fast twist rates, less starting pressure, and continues to seal better all the way to the muzzle. The 5R rifling is easier on the jackets, and lefthand rotation helps decrease coriolis effect in the Northern hemisphere. I have also done this with great success on my 338 Lapua. In fact I just read Frank Galli's book on precision rifle where he is suggesting this same thing. It really is worth it!