Twist & Shout
Posted by KAT on 18th Aug 2015
SAA offers a few different twist rates for their Complete Uppers and barrels. All modern rifle (and pistol) barrels have rifling cut (or pressed) into the bore (inside). This rifling is called lands and groves and these grip the bullet and cause it to spin. The rifling imparts a spin on the bullet as it travels down the barrel. The twist rate is expressed as the the distance the bullet travels to make the bullet twist or spin one revolution. So a barrel with a twist rate of 1:8 will spin the bullet one revolution in 8 inches.
The lands and grooves can be cut in a traditional way drawing a mandrel down the barrel or can be hammer forged like Black Hole Weaponry barrels to achieve a hexagonal rifling which some say offers better accuracy.
So like throwing a football, a bullet needs to have a certain spin on it to stabilize it and help it fly true. There is not one twist rate for all bullets and barrels. Different barrels and different bullets require a different twist to achieve the best ballistics.
Heavier bullets usually fly better with lower twist (1:10 or 1:11) while smaller, lighter bullets need a faster spin rate to fly true (1:7 or 1:8) or stabilize. Some folks compromise and use a twist rate that while not ideal for all the different types of bullets is adequate. Competition shooters will always try and maximize accuracy and only shoot a certain bullet in a rifle with a certain twist.
We have found that a 1:8 twist is good all round barrel twist for AR15 rifles. It works well for 55 grain bullets but is also good for 40 grain and 62 grain.