Tgace
Grandmaster
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twist and shoot the things worth believing in
A little something I wrote last year....
Rifling twist rates can be another head scratcher for the new AR owner. The internet is full of different opinions of what is âbestââŠoften times based on what the writer has purchased and is now trying to justify.
Like any topic of a technical nature, âbestâ is a relative term. For the beginner, what you need to learn are some simple rules of thumb to help you base a decision on.
Gun makers realized rather quickly that the accuracy of a firearm improved when the projectile had a âpointy endâ and was spun. The âpointâ gives the projectile a streamlined shape that slices through the atmosphere more efficiently and groves machined into the gun barrel impart spin. The spin keeps the bullet stable along its path of flight and prevents it from wobbling or tumbling end over end, both of which would be bad for accuracy. Anyone who has used a gyroscope in HS science class recalls that a spinning object likes to stay in one place and resists change. Thatâs what you want in a bullet.
The groves in the barrel, as we all know, are called âriflingâ.
A rifle barrels rate of spin is expressed as 1: (X) with 1= âOne full 360 degree rotation of the bulletâ and X= Inches of barrel length.
The most common âCombat ARâ twist rates you will find âoff the shelfâ these days are 1:7, 1:8, and 1:9. Some AR owners like 1:10 and 1:12 barrels and other variants, but in my experience you will find most guys who ârun and gunâ using one of these three.
If you do the math of dividing barrel length by twist you see that in the common 16âł barrel length a 1:7 twist will spin a bullet twice with 2 inches of the barrel still to go. A 1:8 about twice even, and a 1:9 will spin it once with 7 inches of barrel to goâŠso âalmost twiceâ. Based on manufacturing variations thatâs all approximate but there you go.
So âwhats the point?â you are asking?
Well⊠bullets of any given caliber (AKA: diameter) come in various sizes. Differentiated by weight (measured in âgrainsâ), there is an entire rainbow of .223 caliber bullets ranging from tiny 40 grain bullets up to 80 grain whoppers. Because the diameter of the bullet is fixed, what you get are longer projectiles as the weight increases.
Rules of thumb regarding bullet weight:
Due to a lot of math/physics and stuff I canât explain, itâs really the length of the projectile and itâs velocity that determine how much spin it will need to fly straight and stable, not the weight. However, we talk about bullets in âgrainsâ so when pairing bullets to rifling twist you just have to consider two facts.
You would think that âmore is betterâ when it comes to twist, but what happens when small/light bullets are overspun is that they fly to pieces once they exit the barrel. Heavier bullets will âoverstabilizeâ if spun too much. That means the point of the bullet wont come down on the decent end of itâs trajectory.
So which should you get? Well what do you want to do and what size bullet do you want to do it with?
The 1:9 is a common twist rate âoff the shelfâ when you buy an AR. It will work fine with the commonly found 55 grain bullet up to âmediumâ sized projectiles like 69 grain. Depending on your particular barrel it MAY even stabilize âheavyâ bulletsâŠor it may not. Even if it does, variations like temperature and air pressure MAY make it inconsistent with heavy rounds. So out to 300 yards or so 1:9 should be fine. 400-500 yd shots? Probably not so much.
The 1:7 is the current military standard on the M4/M16 and as such is also a commonly found option. It will throw the medium to heavy rounds out past 300 yards. It can also âsufficientlyâ stabilize 55 grain rounds. You wont get exceedingly small groups with 55gr, and while it MAY stabilize a lighter round for farther shots, you are also at the mercy of your individual barrel and environmental factors.
The 1:8 slides the options to the center. Some praise it as the best of both worlds while others deride it as the âJack of all trades, master of noneâ option.
As you can see, in the end all of them can work fine as a general use option. Itâs when you want to specialize in a specific range or hunting environment that a specific combination of bullet/twist becomes the optimum choice.
A little something I wrote last year....
Rifling twist rates can be another head scratcher for the new AR owner. The internet is full of different opinions of what is âbestââŠoften times based on what the writer has purchased and is now trying to justify.
Like any topic of a technical nature, âbestâ is a relative term. For the beginner, what you need to learn are some simple rules of thumb to help you base a decision on.
Gun makers realized rather quickly that the accuracy of a firearm improved when the projectile had a âpointy endâ and was spun. The âpointâ gives the projectile a streamlined shape that slices through the atmosphere more efficiently and groves machined into the gun barrel impart spin. The spin keeps the bullet stable along its path of flight and prevents it from wobbling or tumbling end over end, both of which would be bad for accuracy. Anyone who has used a gyroscope in HS science class recalls that a spinning object likes to stay in one place and resists change. Thatâs what you want in a bullet.
The groves in the barrel, as we all know, are called âriflingâ.
A rifle barrels rate of spin is expressed as 1: (X) with 1= âOne full 360 degree rotation of the bulletâ and X= Inches of barrel length.
The most common âCombat ARâ twist rates you will find âoff the shelfâ these days are 1:7, 1:8, and 1:9. Some AR owners like 1:10 and 1:12 barrels and other variants, but in my experience you will find most guys who ârun and gunâ using one of these three.
If you do the math of dividing barrel length by twist you see that in the common 16âł barrel length a 1:7 twist will spin a bullet twice with 2 inches of the barrel still to go. A 1:8 about twice even, and a 1:9 will spin it once with 7 inches of barrel to goâŠso âalmost twiceâ. Based on manufacturing variations thatâs all approximate but there you go.
So âwhats the point?â you are asking?
Well⊠bullets of any given caliber (AKA: diameter) come in various sizes. Differentiated by weight (measured in âgrainsâ), there is an entire rainbow of .223 caliber bullets ranging from tiny 40 grain bullets up to 80 grain whoppers. Because the diameter of the bullet is fixed, what you get are longer projectiles as the weight increases.
Rules of thumb regarding bullet weight:
- Lighter bullets can achieve faster velocities and shoot with a flatter trajectory. Their lack of mass means they wont stay stable at longer ranges and wind has more effect on them at long range.
- Heavier bullets will stay stable over longer distances but have a more âarchedâ trajectory. Wind has less effect on them at long range.
- The terminal effect of a bullet, or its âstrikingâ power, is due to a combination of itâs mass and velocity.
- Heavier bullets cost more.
Due to a lot of math/physics and stuff I canât explain, itâs really the length of the projectile and itâs velocity that determine how much spin it will need to fly straight and stable, not the weight. However, we talk about bullets in âgrainsâ so when pairing bullets to rifling twist you just have to consider two facts.
- Lighter bullets need less spin to get them into a stable flight.
- Heavier bullets need more spin to get them stable in flight.
You would think that âmore is betterâ when it comes to twist, but what happens when small/light bullets are overspun is that they fly to pieces once they exit the barrel. Heavier bullets will âoverstabilizeâ if spun too much. That means the point of the bullet wont come down on the decent end of itâs trajectory.
So which should you get? Well what do you want to do and what size bullet do you want to do it with?
The 1:9 is a common twist rate âoff the shelfâ when you buy an AR. It will work fine with the commonly found 55 grain bullet up to âmediumâ sized projectiles like 69 grain. Depending on your particular barrel it MAY even stabilize âheavyâ bulletsâŠor it may not. Even if it does, variations like temperature and air pressure MAY make it inconsistent with heavy rounds. So out to 300 yards or so 1:9 should be fine. 400-500 yd shots? Probably not so much.
The 1:7 is the current military standard on the M4/M16 and as such is also a commonly found option. It will throw the medium to heavy rounds out past 300 yards. It can also âsufficientlyâ stabilize 55 grain rounds. You wont get exceedingly small groups with 55gr, and while it MAY stabilize a lighter round for farther shots, you are also at the mercy of your individual barrel and environmental factors.
The 1:8 slides the options to the center. Some praise it as the best of both worlds while others deride it as the âJack of all trades, master of noneâ option.
As you can see, in the end all of them can work fine as a general use option. Itâs when you want to specialize in a specific range or hunting environment that a specific combination of bullet/twist becomes the optimum choice.
