As long range rimfire shooters we are constantly involved in the pursuit of perfect accuracy. Understanding how barrel twist matches your application is paramount in attaining that goal.
Barrel groove twist rate can have a drastic affect on accuracy if bullet spin is too fast or too slow for bullet design and weight.
Generally speaking a heavier bullet requires more spin in order to stabilize and prevent yaw which if present, can cause groups to open up considerably.
If you are a pilot you know exactly what yaw is. If not, it is basically when the bullet nose wobbles as it moves down range instead of being that perfect spiral like a Drew Breeze bomb to the end zone.
What is barrel twist?
Barrel twist rate refers to how many inches it takes for the bullet to turn once in the barrel during the shot. The turning of the bullet is caused by the rifling machined into the barrel at the factory. A standard 22lr twist rate is 1:16 or 1 turn in 16 inches of barrel travel.
Generally speaking a heavier bullet requires a faster turn in order to stabilze during flight and prevent yaw. 22 lr bullets can be purchase in different weights from 60 grains down to 32 grains with jackets made from lead, copper, plastic, etc and in any speed from 600 fps to 2800 fps. They will not all perform the same out of a given barrel.
This is why it is necessary to find the ammo your rifle likes in order to attain an acceptable accuracy level or to know what bullet you will use for a given purpose and purchase the barrel with the correct twist rate. The standard 1:16 twist rate is designed for 40 grain bullets in the 1000 – 1200 fps range but will handle most of the others pretty well.
What else affects bullet spin and accuracy of a rifle?
A build up of hard residue in the barrel nullifies the effect of rifling and therefore the rate of twist. This can be corrected with a proper cleaning regimen every 300-400 rounds in a rimfire rifle.
Bullets that are moving too fast for the twist can require a more aggressive twist in order to stabilize the bullet properly and at long range.
Damage to the crown or muzzle can definitely affect accuracy and if this is the case, the spin rate won’t atter until this is addressed. If you can see rust or obvious damage to the threads at your muzzle, have a gunsmith inspect it.