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Philip Van Cleave
Philip Van Cleave, Firearms Instructor
Category: Firearms
Satisfied Customers: 3782
Experience:  Firearms instructor, 40 years experience with firearms.
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what does an 8 to 1 twist in a rifle barrel mean ?

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what does an 8 to 1 twist in a rifle barrel mean ?
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For a bullet to be accurate, it must be spinning when it leaves the barrel of a firearm. Much like when a quarterback throws a football, it's only accurate because of the spin he puts on the ball as he throws it.

Gun barrels have spiraling grooves in them called "rifling" that makes a bullet spin.

An 8 to 1 twist means that for every 8 inches a bullet moves down the barrel, the bullet rotates one full turn. So for a 16 inch barrel the bullet will turn twice.

The bigger the first number, the slower the bullet will rotate. A 12 to 1 barrel that is 16 inches long would cause the bullet to rotate 1-1/3 times during its travel down the barrel.

Why would one care about the twist? Because if a bullet spins to slowly, it will tumble and be inaccurate. If too fast the bullet can actually spin apart in mid flight!

The higher spin rates are recommended for longer bullets, such as boattails. The spin rates are also determined by how fast the bullet can go. For faster bullets, the spin rates are slower.

In an AR-15 the 8 to 1 is used to better stabilize the longer, heavier match bullets in the 77 to 80 grain range. For steel core 62 grain bullets, 9 to 1 is used. For lighter bullets traveling very fast, a 12 to 1 is used.

That's not to say you can't use a 62 grain steel core bullet in a 8 to 1 twist barrel, or in a barrel with a 12 to 1 twist for that matter, but it is simply not the optimum rate.

I hope this helps. If you are satisfied with my answer, please click the "accept" button. Thanks!

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