Barrel Twist Rates

socom58 · February 19, 2006, 04:06 AM

Can someone explain to me the concept of barrel twist or recommend a site that's good? Just looking at one caliber (.223 for example), I see anything from 1 in 7 all the way up to 1 in 12 twist rates. The lower the number, the faster the twist, right? How does this relate to the weight of bullet that can be fired and accuracy and such? Thanks

mete · February 19, 2006, 05:11 AM

The twist rate is related to the length of a bullet rather than the weight .So a 180 pointed needs tighter twist than a 180 RN. The figures give you the distance for one complete revolution - 1 in 12" means the bullet rotates one complete turn in 12" . So the longer [and in general the heavier ] the bullet the tighter the twist necessary. ...The 1 in 7" in the 223 is for some very long military bullets. If the twist is not tight enough the bullet will not be stable and tend to tumble and not be accurate.

joshua · February 19, 2006, 06:57 AM

what mete said.

Art Eatman · February 19, 2006, 11:57 AM

Hidden away somewhere in the Search feature of TFL is a formula for calculating the twist rate for various bullets. Sorry, but I've lost the location of wherever I wrote it down.

The formula gives a good aproximation...

Art

ribbonstone · February 19, 2006, 12:04 PM

Most twists are a little fast for the typical bullets we use...doesn't do a world of harm to slightly overspin but a drastic overspin usually gives less accuracy (and "why" is basically becasue of small bullet imprefections...with a "perfect" bullet shuld be able to spin the snot out of it). The 1:10 twist of most 30-06's is from the days of 220gr. RN bullets (in the 30-40 and 30-03 as well). Some of today's bullets are of the LENGTH of that old 220gr. RN, but most 30-06 shooteres are using shorter bullets that really don't need that much spin.

Overspinning can add stress to light weight bullets that are drastically overspun, but as any 22/250 or .220swift shooter can tell you, can still be accurate so long as they hold togeter. Same holds true for .223's 1:7 or 1:9 twist; if the bullets are balanced and strong enough, can still shoot well.

Underspinning is the problem...like tossing a football with no spin to it, they tend to tumble end for end.
-------
Don't put barrel elngth into the equation...has nothing to do with it (except for adding some velocity). Think of two bolts and two nuts, each of the same pitch thread...no matter how long the bolt, the nut is going to turn at the same rate.

Jim Watson · February 19, 2006, 12:16 PM

The Greenhill formula gives a very approximate approximation, being based on late XIX century velocities and bullet (actually light artillery shell) shapes. There are better calculations but they get pretty involved.

I think the best thing to do on twist rates is to go with the standard for the calibre. If you want to do something unusual, best get in touch with shooters and gunsmiths with actual experience in the field.

The .223 is kind of a oddball because it has had so many incarnations over its history. When new they treated it like any other .22 centerfire varmint calibre. A 14 inch twist had served for 50-55 grain flatbase spitzer bullets for many years in many rifles. But it was not enough for cheap boattails in cold air so they went to a 12 inch twist in Vietnam era M16s. Then they wanted longer range. Target shooters went to a 9 inch twist for the 69 grain match bullets, heaviest available at the time. That was enough for the new 62 grain three piece SS109/M855 bullet but they had to go to a 7 inch twist to stabilize the very long SS110/M856 tracer bullet. Now the target shooters are using 80 grain bullets in 7.5-8 inch twists and Sierra has introduced a 90 grain bullet for a recommended 6.5 inch twist. I have one of those and it does not do everything I had hoped for, but it has its points.

So there it depends on what you want to do.

socom58 · February 19, 2006, 02:13 PM

I would be shooting 55 or 62 grain stuff primarily. I can't see ever shooting aything heavier than maybe a 69 or 77 gr. match load and that would be rare. Would a 1 in 8" or 1 in 9" twist serve me best then?

Jim Watson · February 19, 2006, 03:30 PM

A 9 inch twist is fine for 62 grain military and 69 grain match and will usually shoot lighter bullets pretty well.

I don't know if it would stabilize a 77 grain bullet. An 8 inch twist definitely would, but they are not common. Some Rock River ARs have 8 twist barrels.

dirksterg30 · February 20, 2006, 09:50 AM

Check out www.ammo-oracle.com - loads of info for the AR-15 owner.

Chris Phelps · February 20, 2006, 10:06 AM

Model 1 varnmit kits offer a 1 in 8 and 1 in 9 option at no extra cost.

That website in the post above mine is incredibly interesting... thanks for sharing!

MrGee · February 20, 2006, 12:42 PM

This information is straight from the Shilen web page at: http://www.shilen.com/calibers.htm

"The information below will help you select the best barrel twist for your specific needs, providing of course there are multiple choices. If you’ll be shooting one bullet weight, choose a twist from the chart just fast enough to stabilize it. Too fast a twist simply overspins the bullet and may result in reduced accuracy. On the other hand, a twist too slow for any bullet will likely produce instability, keyholing and rotten accuracy. So if you’re going to be using several bullet weights, be sure to select a twist that will stabilize the heaviest one, since lighter bullets will also be stabilized.

By way of explanation, the numbers in the "Twist" column indicate how far the bullet must travel through the bore to make one full revolution. This is determined by the rate of rotation of the rifling. For example, a 9"-twist barrel spins the bullet one full turn when it passes 9 inches through the bore. In a 16"-twist barrel, the bullet makes one revolution in 16 inches. So at the same bullet velocity, the 9" twist is faster (spins the bullet faster) than the 16" twist. Consequently, as the chart reflects in the .224 CF section, the 9" twist is necessary for stabilizing heavier bullet weights.

Again looking at the .224 CF section, if you’re planning to shoot 55-grain bullets, the 14" twist is ideal. This twist is also the best choice for 52- and 53-grain match bullets driven at moderate velocities. But if you’re also contemplating shooting a 60-grainer, go with the 12" twist, since it will stabilize all the bullets you’ll be using. As you can see from the 15" and 16" twists, higher velocities also spin the bullet faster and may enable a slower-than-recommended twist to stabilize a marginally overweight bullet. However, this is tricky stuff best left to those who are highly experienced in operating at the ragged edge of stability and sanity.

The basic principles just outlined apply to all the calibers below. But, if you have questions or need a recommendation, let us know.

Caliber Twist

.172 9" For bullets heavier than 30 gr.

10" For bullets up to 30 gr.

.204/20 12" For all bullets.

.222 RF 14"* Twist for pistol barrels

16" Standard twist for rifle barrels

17"* Special twist for rifle barrels

.224 CF 8" For bullets heavier than 70 gr.

9" For bullets up to 70 gr.

12" For bullets up to 63 gr.

14" For bullets up to 55 gr.

15"* For bullets up to 55 gr. driven 4,100 fps or more

16"* For bullets up to 55 gr. driven 4,300 fps or more

6mm/.243 8" Special for VLD bullets over 100 gr.

10" For bullets up to 120 gr. and VLD under 100 gr.

12" For bullets up to 85 gr.

13"* For bullets up to 75 gr.

14"* For bullets up to 70 gr.

15"* Special for bullets up to 70 gr.

.257 9" For bullets heavier than 100 gr.

10" For bullets up to 100 gr.

12" For bullets up to 90 gr.

13"* For bullets up to 80 gr.

14"* For bullets up to 70 gr.

6.5mm/.264 8" For bullets heavier than 130 gr.

9" For bullets up to 130 gr.

.270 10" For all bullets

7mm/.284 9" For bullets heavier than 140 gr.

11" For bullets up to 140 gr.

.307 13"* Special size and twist

.308 8" For bullets heavier than 220gr.

10" For bullets up to 220 gr.

12" For bullets up to 170 gr.

14"* For bullets up to 168 gr.

15"* For bullets up to 150 gr.

7.65mm/.311 10" For all bullets

8mm/.323 10" For all bullets

.338 10" For all bullets

9mm/.355 14" For low-velocity wadcutters

16" For all other bullets

.38/.357 14" For low-velocity wadcutters

18" For all other bullets

.358 14" For all bullets

.375 12" For all bullets

10mm/.400 16" For all bullets

.411 14" For all bullets

.416 14" For all bullets

.44 20" For all bullets

16" For low velocity wadcutters

.451 16" For all bullets

.458 14" For all bullets

*Stainless steel only

Black powder barrels (1.250" x 30")

.32 14" .320" groove

.38 20" . 379" groove

.40 20" .403" groove

.457 20", 14" .457" groove"

NC.Mr.G

February 19, 2006, 04:06 AM	#1
socom58 Senior Member Join Date: December 13, 2004 Location: People's Republic of California Posts: 176	Barrel Twist Rates Can someone explain to me the concept of barrel twist or recommend a site that's good? Just looking at one caliber (.223 for example), I see anything from 1 in 7 all the way up to 1 in 12 twist rates. The lower the number, the faster the twist, right? How does this relate to the weight of bullet that can be fired and accuracy and such? Thanks __________________ Scientia est potentia.

February 19, 2006, 02:13 PM	#7
socom58 Senior Member Join Date: December 13, 2004 Location: People's Republic of California Posts: 176	I would be shooting 55 or 62 grain stuff primarily. I can't see ever shooting aything heavier than maybe a 69 or 77 gr. match load and that would be rare. Would a 1 in 8" or 1 in 9" twist serve me best then? __________________ Scientia est potentia.

February 20, 2006, 09:50 AM	#9
dirksterg30 Senior Member Join Date: May 18, 2005 Location: Pittsburgh, PA Posts: 563	Check out www.ammo-oracle.com - loads of info for the AR-15 owner. __________________ Visit my webstore Right Wing Things for quality conservative gear, including gun-related and anti-Obama bumper stickers.

February 20, 2006, 10:06 AM	#10
Chris Phelps Senior Member Join Date: December 15, 2005 Location: South China, Maine Posts: 814	Model 1 varnmit kits offer a 1 in 8 and 1 in 9 option at no extra cost. That website in the post above mine is incredibly interesting... thanks for sharing! __________________ Bushmaster Superlight AR-15 5.56mm / Custom 24" Heavy BBL Varmint AR-15 5.56mm / Ruger M77 .257 Roberts / Ruger MKI 22LR Pistol / EAA Witness 9mm Pistol / Daisy 2202 22LR / Remington Viper 522 22LR / Stevens 200 .223 / Savage 10FP 24" .308 / Mauser 98 Sporter 30-06

February 19, 2006, 05:11 AM	#2
mete Senior Member Join Date: June 14, 2004 Location: NY State Posts: 6,575	The twist rate is related to the length of a bullet rather than the weight .So a 180 pointed needs tighter twist than a 180 RN. The figures give you the distance for one complete revolution - 1 in 12" means the bullet rotates one complete turn in 12" . So the longer [and in general the heavier ] the bullet the tighter the twist necessary. ...The 1 in 7" in the 223 is for some very long military bullets. If the twist is not tight enough the bullet will not be stable and tend to tumble and not be accurate.

February 19, 2006, 06:57 AM	#3
joshua Senior Member Join Date: October 27, 2004 Location: norCal Posts: 2,161	what mete said.

February 19, 2006, 11:57 AM	#4
Art Eatman Staff in Memoriam Join Date: November 13, 1998 Location: Terlingua, TX; Thomasville, GA Posts: 24,798	Hidden away somewhere in the Search feature of TFL is a formula for calculating the twist rate for various bullets. Sorry, but I've lost the location of wherever I wrote it down. The formula gives a good aproximation... Art

February 19, 2006, 12:04 PM	#5
ribbonstone Senior Member Join Date: January 29, 2006 Posts: 179	Most twists are a little fast for the typical bullets we use...doesn't do a world of harm to slightly overspin but a drastic overspin usually gives less accuracy (and "why" is basically becasue of small bullet imprefections...with a "perfect" bullet shuld be able to spin the snot out of it). The 1:10 twist of most 30-06's is from the days of 220gr. RN bullets (in the 30-40 and 30-03 as well). Some of today's bullets are of the LENGTH of that old 220gr. RN, but most 30-06 shooteres are using shorter bullets that really don't need that much spin. Overspinning can add stress to light weight bullets that are drastically overspun, but as any 22/250 or .220swift shooter can tell you, can still be accurate so long as they hold togeter. Same holds true for .223's 1:7 or 1:9 twist; if the bullets are balanced and strong enough, can still shoot well. Underspinning is the problem...like tossing a football with no spin to it, they tend to tumble end for end. ------- Don't put barrel elngth into the equation...has nothing to do with it (except for adding some velocity). Think of two bolts and two nuts, each of the same pitch thread...no matter how long the bolt, the nut is going to turn at the same rate.

February 19, 2006, 12:16 PM	#6
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	The Greenhill formula gives a very approximate approximation, being based on late XIX century velocities and bullet (actually light artillery shell) shapes. There are better calculations but they get pretty involved. I think the best thing to do on twist rates is to go with the standard for the calibre. If you want to do something unusual, best get in touch with shooters and gunsmiths with actual experience in the field. The .223 is kind of a oddball because it has had so many incarnations over its history. When new they treated it like any other .22 centerfire varmint calibre. A 14 inch twist had served for 50-55 grain flatbase spitzer bullets for many years in many rifles. But it was not enough for cheap boattails in cold air so they went to a 12 inch twist in Vietnam era M16s. Then they wanted longer range. Target shooters went to a 9 inch twist for the 69 grain match bullets, heaviest available at the time. That was enough for the new 62 grain three piece SS109/M855 bullet but they had to go to a 7 inch twist to stabilize the very long SS110/M856 tracer bullet. Now the target shooters are using 80 grain bullets in 7.5-8 inch twists and Sierra has introduced a 90 grain bullet for a recommended 6.5 inch twist. I have one of those and it does not do everything I had hoped for, but it has its points. So there it depends on what you want to do.

February 19, 2006, 03:30 PM	#8
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	A 9 inch twist is fine for 62 grain military and 69 grain match and will usually shoot lighter bullets pretty well. I don't know if it would stabilize a 77 grain bullet. An 8 inch twist definitely would, but they are not common. Some Rock River ARs have 8 twist barrels.

February 20, 2006, 12:42 PM	#11
MrGee Senior Member Join Date: June 7, 2005 Location: NC Posts: 260	This information is straight from the Shilen web page at: http://www.shilen.com/calibers.htm "The information below will help you select the best barrel twist for your specific needs, providing of course there are multiple choices. If you’ll be shooting one bullet weight, choose a twist from the chart just fast enough to stabilize it. Too fast a twist simply overspins the bullet and may result in reduced accuracy. On the other hand, a twist too slow for any bullet will likely produce instability, keyholing and rotten accuracy. So if you’re going to be using several bullet weights, be sure to select a twist that will stabilize the heaviest one, since lighter bullets will also be stabilized. By way of explanation, the numbers in the "Twist" column indicate how far the bullet must travel through the bore to make one full revolution. This is determined by the rate of rotation of the rifling. For example, a 9"-twist barrel spins the bullet one full turn when it passes 9 inches through the bore. In a 16"-twist barrel, the bullet makes one revolution in 16 inches. So at the same bullet velocity, the 9" twist is faster (spins the bullet faster) than the 16" twist. Consequently, as the chart reflects in the .224 CF section, the 9" twist is necessary for stabilizing heavier bullet weights. Again looking at the .224 CF section, if you’re planning to shoot 55-grain bullets, the 14" twist is ideal. This twist is also the best choice for 52- and 53-grain match bullets driven at moderate velocities. But if you’re also contemplating shooting a 60-grainer, go with the 12" twist, since it will stabilize all the bullets you’ll be using. As you can see from the 15" and 16" twists, higher velocities also spin the bullet faster and may enable a slower-than-recommended twist to stabilize a marginally overweight bullet. However, this is tricky stuff best left to those who are highly experienced in operating at the ragged edge of stability and sanity. The basic principles just outlined apply to all the calibers below. But, if you have questions or need a recommendation, let us know. Caliber Twist .172 9" For bullets heavier than 30 gr. 10" For bullets up to 30 gr. .204/20 12" For all bullets. .222 RF 14"* Twist for pistol barrels 16" Standard twist for rifle barrels 17"* Special twist for rifle barrels .224 CF 8" For bullets heavier than 70 gr. 9" For bullets up to 70 gr. 12" For bullets up to 63 gr. 14" For bullets up to 55 gr. 15"* For bullets up to 55 gr. driven 4,100 fps or more 16"* For bullets up to 55 gr. driven 4,300 fps or more 6mm/.243 8" Special for VLD bullets over 100 gr. 10" For bullets up to 120 gr. and VLD under 100 gr. 12" For bullets up to 85 gr. 13"* For bullets up to 75 gr. 14"* For bullets up to 70 gr. 15"* Special for bullets up to 70 gr. .257 9" For bullets heavier than 100 gr. 10" For bullets up to 100 gr. 12" For bullets up to 90 gr. 13"* For bullets up to 80 gr. 14"* For bullets up to 70 gr. 6.5mm/.264 8" For bullets heavier than 130 gr. 9" For bullets up to 130 gr. .270 10" For all bullets 7mm/.284 9" For bullets heavier than 140 gr. 11" For bullets up to 140 gr. .307 13"* Special size and twist .308 8" For bullets heavier than 220gr. 10" For bullets up to 220 gr. 12" For bullets up to 170 gr. 14"* For bullets up to 168 gr. 15"* For bullets up to 150 gr. 7.65mm/.311 10" For all bullets 8mm/.323 10" For all bullets .338 10" For all bullets 9mm/.355 14" For low-velocity wadcutters 16" For all other bullets .38/.357 14" For low-velocity wadcutters 18" For all other bullets .358 14" For all bullets .375 12" For all bullets 10mm/.400 16" For all bullets .411 14" For all bullets .416 14" For all bullets .44 20" For all bullets 16" For low velocity wadcutters .451 16" For all bullets .458 14" For all bullets *Stainless steel only Black powder barrels (1.250" x 30") .32 14" .320" groove .38 20" . 379" groove .40 20" .403" groove .457 20", 14" .457" groove" NC.Mr.G