Twist rate and barrel length are completely independent of each other. A 1:48" twist barrel can be 36" long, or 6" long, but if the muzzle velocity is the same, the rate of the revolution of the bullet will be the same. Twist rate simply refers to the pitch of the rifling in turns per distance. Obviously, the faster the bullet is moving, the quicker it's spinning. The twist rate of a barrel is determined based on the minimum spin required to stabilize the longest projectile that's likely to be fired at the muzzle velocity that the gun will reasonably achieve with that projectile. Shorter/lighter bullets will likely be fired at a higher velocity, and therefore a greater rate of spin, and will be stable.

The problem is that it is possible to overstabilize a projectile, and in some cases too fast a twist can damage the projectile because it does not firmly engage the rifling and effectively skids across the lands until it grabs and spins. This is problem with patched roundballs and loose fitting (read easy loading) soft lead conicals. With ML's, because of the extreme range of projectile lengths, types and "typical" velocities, the manufacturers can't easily settle on one twist rate like is usually possible for CF rifles. The 1:66" twist that's optimal for patched RB won't stabilize most conicals or sabot projectiles. A 1:28" twist will stabilize all but the longest sabot and conical bullets, but is way too fast for accuracy with roundballs or "Pennsylvania conicals." The 1:48" twist rate is a compromise meant to provide adequate performance with PRB's and lighter for caliber conical bullets and sabots.

Mike