What is the difference between a 1:7 twist and a 1:9 twist? Besides for the obvious of one having a full twist in 7" and one in 9". I mean, what are the advantages/disadvantages? Does it effect the bullet?
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Twist rate ?
- Thread starter rather-b-shootin
- Start date
In general. A lighter faster bullet would tend to shoot better from a lesser twist, and a heavier slower bullet would shoot better from a tighter / faster twist. If you are talking about an AR however, those are both great twists and unless you are using the gun for long range competition you won't be able to tell the difference.
J
Jose
The faster the rifling twist is, the longer the bullet that it can stabilize.
Longer bullets need more rotational velocity to be gyroscopically stable than shorter ones. Since for a given caliber bore diameter is fixed, longer bullets are proportionally heavier than shorter ones.
Hence common perception is that faster twist barrels are necessary for stabilizing heavier bullets. While that is generally true when speaking of lead cored, copper jacketed bullets, all-copper bullets (like the Barnes-X bullet) are different.
For example, a 1/9 20" barrel is sufficient to stabilize a 70 grain lead/copper bullet in .224" diameter. But an all copper bullet of the same weight HAS to be longer and thus will most likely keyhole out of the same barrel at a similar muzzle velocity. So all copper bullets need faster twists than lead cored bullets of the same weight.
Longer bullets need more rotational velocity to be gyroscopically stable than shorter ones. Since for a given caliber bore diameter is fixed, longer bullets are proportionally heavier than shorter ones.
Hence common perception is that faster twist barrels are necessary for stabilizing heavier bullets. While that is generally true when speaking of lead cored, copper jacketed bullets, all-copper bullets (like the Barnes-X bullet) are different.
For example, a 1/9 20" barrel is sufficient to stabilize a 70 grain lead/copper bullet in .224" diameter. But an all copper bullet of the same weight HAS to be longer and thus will most likely keyhole out of the same barrel at a similar muzzle velocity. So all copper bullets need faster twists than lead cored bullets of the same weight.
awesome. got it, thank you!
Taipan01
NES Member
This is a dupe from a previous posting. Should help a bit:
"For the heavies:1x7. It is technically too tight of a twist for most of the .224 bullets that are widely available. It was manufactured originally to stabilize SS109 and/or tracer ammo (mainly for the tracers elongated bullet) but upon further military testing, other twists were shown to be superior. Long range shooters using the heavier 75-90's will fair better using this or the 1X8 twist. The 1x8:This twist is great for 69-80 grain bullets. The more common 1x9: This is a good all around twist ratio. It is best suited for 52-69 grain. Though I've used it with Varmint loads about 40 grain going close to 4,000 fps with really good results. For the most part I run with this twist using 55 & 62 grain. The 1x10: Almost the same as 1x9, but favors the lighter side a little more. The 1x12: This tends toward the 40-52 grain bullets. This twist is commonly found on bolt actions that are primarily used as varminteers. They are okay up to 55, but not really the best. 1x14: Use this one if you are into tumbling effects and keyholeing".
"For the heavies:1x7. It is technically too tight of a twist for most of the .224 bullets that are widely available. It was manufactured originally to stabilize SS109 and/or tracer ammo (mainly for the tracers elongated bullet) but upon further military testing, other twists were shown to be superior. Long range shooters using the heavier 75-90's will fair better using this or the 1X8 twist. The 1x8:This twist is great for 69-80 grain bullets. The more common 1x9: This is a good all around twist ratio. It is best suited for 52-69 grain. Though I've used it with Varmint loads about 40 grain going close to 4,000 fps with really good results. For the most part I run with this twist using 55 & 62 grain. The 1x10: Almost the same as 1x9, but favors the lighter side a little more. The 1x12: This tends toward the 40-52 grain bullets. This twist is commonly found on bolt actions that are primarily used as varminteers. They are okay up to 55, but not really the best. 1x14: Use this one if you are into tumbling effects and keyholeing".
Obviously long bullets that don't have a fast enough twist aren't as stable or stable enough. What happens if the shorter bullet is spun faster than ... "normal" I guess? Are you better off getting a 1:7 barrel even if you won't usually be shooting long bullets, but may shoot them every once in a while?
J
Jose
I have shot LOTS of 45 grain WW White Box ammo at the 200 yard line for offhand and stitting practice in Highpower Rifle and I never lost one when shot through a 1/7 barrel.
So yes. Get the fastest rifling rate you can find. It simply gives you more options with no penalties.
This subject is caveman simple but it generates threads of epic proportions at Arfcom with idiots arguing all kinds of nonsense like their claim that faster twist barrels "wear out" faster.
When a bullet engages the rifling, the rifling imparts a spin to the bullet (obviously) To do this, the rifling exerts a tangential force to the jacket of the bullet. The exact angle of this force is set by the twist rate. At a twist rate of 1:3.14", this angle is roughly 45 degrees. At 1:7 you're about 22 degrees and almost 15 degrees at 1:9.
Faster twist rates will stabilize a longer bullet further in flight and longer in a target, so what's the cost?
Faster twist rates have a higher tangential angle, thus more of the engaging forced acts against the bullet's forward momentom. That means higher chamber pressure and lower velocity. That's why S&W selected a progressive twist for their .460 S&W Magnum bullets, so they initial engagement with the rifling is at 1:100" to limit backforce and resulting increased pressure.
The more stable bullet will also tend to tumble less in-target, so have slightly lower wound tramua.
The general thought is to select the barrel that will just stabilize the longest bullet you will shoot at the longest range you will shoot it.
Faster twist rates will stabilize a longer bullet further in flight and longer in a target, so what's the cost?
Faster twist rates have a higher tangential angle, thus more of the engaging forced acts against the bullet's forward momentom. That means higher chamber pressure and lower velocity. That's why S&W selected a progressive twist for their .460 S&W Magnum bullets, so they initial engagement with the rifling is at 1:100" to limit backforce and resulting increased pressure.
The more stable bullet will also tend to tumble less in-target, so have slightly lower wound tramua.
The general thought is to select the barrel that will just stabilize the longest bullet you will shoot at the longest range you will shoot it.
