Written by Sierra Bullets Ballistic Technician Paul Box
Based on the questions we get on a daily basis on our 800 line, twist is one of the most misunderstood subjects in the gun field. So let’s look deeper into this mystery and get a better understanding of what twist really means.
When you see the term 1-14″ or 1-9″ twist, just exactly what does this mean ? A rifle having a 1-14″ twist means the bullet will rotate one complete revolution every fourteen inches of the barrel. Naturally a 1-9″ turns one time every nine inches that it travels down the barrel. Now, here’s something that some people have trouble with. I’ve had calls from shooters thinking that a 1-14″ twist was faster than a 1-9″ because the number was higher with the 1-14″. The easiest way to remember this is the higher the number, the slower the twist rate is.
Now, the biggest misconception is that if a shooter has a .223 with a 1-8″ twist, his rifle won’t stabilize a 55 gr. bullet or anything lighter. So let’s look at what is required. The longer a bullet is for its’ diameter, the faster the twist has to be to stabilize it. In the case of the .223 with a 1-8″ twist, this was designed to stabilize 80 gr. bullets in this diameter. In truth the opposite is true. A 1-8″ will spin a 55 gr. faster than what is required in order to stabilize that length of bullet. If you have a bullet with good concentricity in its jacket, over spinning it will not hurt its’ accuracy potential.
Think of it like tires on your truck. If you have a new set of tires put on your truck, and they balance them proper at the tire shop, you can drive down a street in town at 35 MPH and they spin perfect. You can get out on the highway and drive 65 MPH and they still spin perfect. A bullet acts the same way.
Once I loaded some 35 gr. HP bullets in a 22-250 Ackley with a 1-8″ twist. After putting three shots down range, the average velocity was 4584 FPS with an RPM level of 412,560. The group measured .750″ at 100 yds. This is a clear example that it is hard to over stabilize a good bullet.