What is twist rate? First let's talk about rifling. Rifling consists of grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm. Rifling is placed in the barrels of firearms to impart a spin on the bullets. Twist is the amount of turns the rifling has to spin the bullet. Expressed in terms of the number of revolutions per inch of barrel length, this ratio is commonly expressed by designations such as 1:10, 1/10 or 1 in 10 twist, the 1 represents 1 twist, the 10 represents inches of barrel length.
What does the twist rate do:
The rate of twist determines the optimum bullet weight for a given caliber and speed of the bullet by applying the proper spin on the bullet to prevent the bullet form yawing and pitching.
How do you know what's right
A good rule of thumb is that the heavier and longer a bullet is, the faster the twist rate needs to be. A lighter shorter bullet needs a slower twist rate to give proper bullet spin.
Exception to the rule:
Over stabilization of bullets can occur when larger heavier bullets are fired at very high velocities.