Never Let Your Left Hand Know....
Q: I was interested to read your comments about right vs lefthand twist in rifling. There is no ballistic advantage of one over the other; the Coriolis effect is zero over normal shooting ranges. Newton's third law of motion (the action/reaction one) gets a fair workout when any gun/rifle is fired. One thing I have never seen mentioned is the torque reaction imparted on the rifle by the rotation of the projectile created by the rifling twist. This force is proportional to the square of the angular velocity, which is considerable. A projectile traveling at say 3000fps in a barrel with a 1:10" righthand twist is rotating 3600 times a second clockwise. The torque reaction kicks the stock anticlockwise (to the left) into a righthand shooter's cheekbone which can be painful after a number of shots. I reckon a rifle manufacturer would have a marketing advantage if they negated this by putting a barrel with a lefthand twist on a righthanded rifle and a barrel with a righthand twist on a lefthanded rifle. The cost would be negligible and felt recoil would certainly be reduced. What do you think?
A: Afraid I've never had the experience of having the stock kicked anti-clockwise with enough force to bruise my cheekbone, and I've shot some powerful rifles in my time. However, on a few occasions when shooting real ultralight rifles, I've had the rifle actually try to twist itself out of my hands. This was most pronounced with a light rifle which had a titanium receiver. This torque is probably caused by a twisting or rotating tendency created by force being applied to the receiver. Torque is calculated by the multiplication of the force and the shortest perpendicular distance of the force. As you mentioned, energy from rotary motion is equal to torque times angular displacement. The torque twist is an opposite reaction to the rifling in the barrel which is forcing the bullet to turn one way as it turns the gun the opposite way. It is normally experienced in big magnum handguns and lightweight rifles firing high velocity cartridges. And indeed, it would be correct to say that it was Newton's third law of motion in operation once again. Putting different twist barrels on right and lefthanded rifles would not reduce recoil to any noticeable extent. It would add to the cost as it would require tooling up for two different rifling methods. I can't see any commercial riflemaker being bothered to do that. In any case, why bother?