"Gain Twist", also known as "Progressive twist", is where the first part of the barrel from the breech is a very slow twist, such as 1:96, and gets progressively faster up to the muzzle. Many have found this very helpful with heavier powder loads that can cause "skipping" in the first part of the barrel where the ball/bullet just slides through the rifling without gaining any twist till around midway up the barrel. This causes very unreliable accuracy. With gain twist, the skipping is reduced, most times eliminated, and produces very accurate groups.