The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools
Old August 16, 2013, 10:52 PM   #1
JohnKSa
Staff
 
Join Date: February 12, 2001
Location: DFW Area
Posts: 18,409
.223/5.56 Twist Rate Information

We'll start with some information from bullet sellers. This data is actually compiled from twist rates suggested for individual bullets. Since the length of the bullet, more than the weight is the main issue in determining the required barrel twist these numbers should not be considered applicable to all bullets currently on the market. For example, although Berger recommends a 1:9 twist for 70 grain bullets in general, they do sell some 70 grain bullets that they state will stabilize in a 1:10 twist barrel.

Bullets made of solid copper (or gilding metal or bronze), or bullets with steel cores will be longer for a given weight since those metals are less dense than lead. Because of their additional length, they might not stabilize with the twists recommended for a conventional (copper-jacketed lead core) bullet of the same weight. However, it's safe to consider this general information to be a good starting point.

It is worth remembering that bullet sellers are likely to recommend a faster twist than a slower twist if there's any question about what will work since they want satisfied customers. There's some real world shooting data at the end of the post that demonstrates that their recommendations tend towards the conservative.

Of course, a faster twist (smaller second number--1:7 is a faster twist than 1:8) will always stabilize lighter (shorter) bullets than listed in the charts.

It's also important to keep in mind that higher muzzle velocities will result in a faster spin for a given rifling rate. So a bullet that might be marginally stabilized in a 14" barrel might stabilize just fine out of a 26" barrel with the same twist because of the higher muzzle velocity.

Here's a plot that demonstrates the relationship between muzzle velocity and bullet spin rate. Remember that bullet spin rate is measured in revolutions per second while rifling twist is a measure of how far forward the bullet moves during each revolution. The two things are not the same although they are obviously related.



General Data
Condensed from the old Berger website.
.224 (.223) bullet weight vs barrel twist.
30-45 Grains 1:15 Twist
50-55 Grains 1:14 Twist
60-64 Grains 1:12 Twist
70-75 Grains 1:9 Twist
80 Grains 1:8 Twist
Here's a FAQ answer from the new Berger website
http://www.bergerbullets.com/wp_supe...slowest-twist/
Spinning a bullet faster than necessary can amplify any inconsistency in the bullet. Since we use J4 jackets, you can shoot Berger Bullets in faster twist than what is listed. We list the slowest twist rate needed because we want to squeeze every bit of accuracy out of a rifle.
From Sierra's website
45 Grains 1:16 Twist
50-55 Grains 1:14 Twist
60 Grains 1:12 Twist
65-69 Grains 1:10 Twist
77-80 Grains 1:8 Twist
90 Grains 1:6.5 Twist
Group Size vs. Twist Rate Data
Ok, now for something a little more visual to work with. I compiled the results from two tests. One test was conducted by R. L. Window and Dick Metcalf for an article in Shooting Times Magazine and the other by James Tarr for an article in Guns & Ammo Magazine.

In all, the two tests used 9 rifles with 4 different rifling twists and 17 types of ammunition with 10 different bullet weights.

Here are the results. Notice that even the 1:12 twist stabilized bullets up to 69 grains but that above 69 grains, the bullets are unstable in the slower twists. The 90 grain bullets required at least 1:8 twist to stabilize them and the 77 grain bullets needed at least 1:9 twist.

The reason the lines aren't continuous is that not all bullet weights were tested with all the twists. For example, there was no data for 75grain bullets in a 1:12 twist barrel so there's a break in the line for the 1:12 twist data at the 75 grain point.



Here's the same data from a slightly different perspective. There are two different plots, one shows 7 of the bullet weights--the ones tested in all of the 4 rifling twists that were used in the test. The second one has the remaining 3 bullet weights that were tested in only 2 of the rifling twists used.

I tried to make one plot with all of the bullet weights, but it was misleading due to the fact that not all bullet weights were tested in every rifling twist, so I had to break it into two plots to avoid misunderstandings.





It's worth keeping these graphs in mind. One thing that they show is that in the test rifles, 1:9 twist worked for even 77 grain bullets which are about the top limit of what will fit in an AR magazine. All 3 of the 1:9 twist rifles tested shot the 77 grain bullets well. In other words, in these tests, any .223/5.56 loading that would fit in a typical .223/5.56 magazine were stabilized by a 1:9 twist under the test conditions.

Even the much-maligned 1:12 twist stabilized bullets weighing up to 69 grains.

Keep in mind that the shortest barrel length used for testing 1:9 twist was 20" and the testing was carried out at 100 yards. At longer ranges, or with shorter barrels, or when other conditions significantly reduce muzzle velocity, stabilization problems may occur with very heavy bullets (75 grains and up) when using 1:9 twist.

The following thread provides some input from shooters who have had stabilization issues with short barrels and/or low temperatures, both of which can reduce muzzle velocity and therefore bullet rpm.

http://thefiringline.com/forums/show....php?p=5647756
Attached Images
File Type: jpg WeightvsAccuracyByTwist_Small.jpg (81.9 KB, 490 views)
File Type: jpg TwistvsAccuracyByWeight_Small.jpg (77.7 KB, 458 views)
File Type: jpg TwistvsAccuracyByWeight2_Small.jpg (65.9 KB, 448 views)
__________________
Did you know that there is a TEXAS State Rifle Association?

Last edited by JohnKSa; September 29, 2013 at 07:33 PM. Reason: Added information in blue.
JohnKSa is offline  
Old November 11, 2013, 01:52 PM   #2
Theohazard
Senior Member
 
Join Date: April 19, 2012
Location: Western WA
Posts: 2,208
This is some great info. This thread should be a stickie.
__________________
0331: "Accuracy by volume."
Theohazard is offline  
Old November 12, 2013, 04:05 PM   #3
Metal god
Senior Member
 
Join Date: April 10, 2012
Location: San Diego CA
Posts: 2,029
wow , I mean wow . This thread is going to hurt some guys feelings It does confirm what most of us knew already . I was a little surprised that the 1-9 stabilized the 77s but they were all shot from a 20" or longer barrel at what I assume is 100yds . I would like to see the same test done at 500yds with a 16" barrel and 7 , 8 and 9 twist to see the difference . Maybe even 1/2 that 250 to 300 yards .
__________________
As of this date 8-18-14 at 6:42am I became a proud grandfather I guess I'm officially old
Metal god is offline  
Old November 13, 2013, 12:30 AM   #4
JohnKSa
Staff
 
Join Date: February 12, 2001
Location: DFW Area
Posts: 18,409
Quote:
I would like to see the same test done at 500yds with a 16" barrel and 7 , 8 and 9 twist to see the difference . Maybe even 1/2 that 250 to 300 yards.
So would I. The two articles both involved a tremendous amount of shooting, and they still didn't do much more than scratch the surface when you start considering variables like barrel length, temperature and longer distances than 100 yards.

It helps to explain why the military went with such a fast twist--they are concerned with the possibility of all those variables "ganging up" on them in a bad way. If you combine short barrels, low temperatures and extended ranges then you need a faster twist to compensate for the sum of the effects than would otherwise seem reasonable.
__________________
Did you know that there is a TEXAS State Rifle Association?
JohnKSa is offline  
Old November 13, 2013, 11:17 AM   #5
kraigwy
Senior Member
 
Join Date: June 16, 2008
Location: Wyoming
Posts: 9,472
Maybe not as complete as we might want, but here is the comparison of the 1:12 and 1:7 using 55 gr M193 and the 62 gr M855 at 300 meters.

__________________
Kraig Stuart
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071
kraigwy is offline  
Old November 13, 2013, 11:47 AM   #6
doofus47
Senior Member
 
Join Date: June 9, 2010
Location: live in a in a house when i'm not in a tent
Posts: 1,312
^^^
I'm having a hard time reconciling the two images, Kraigwy's comparison of M193 and M855 target impacts and JonnKSa's "223REM rifling vs accuracy by bullet weight" and other graphs of his that indicate that 1:12 should be fine with 62gr bullets. If the groupings of a 62gr bullet is 1" for a 1:12 twist (presumably at 100 yards). That should translate, in my mind, to 3" groupings (or slightly higher) at 300 yards.
It appears to me that the 1:12 under-stabilizes the M855. Do we know if there was there a difference in muzzle velocity between the M855 and the 223 in the tests above?
I'm curious b/c I always thought that I was "stuck" with 55gr bullets in my Vietnam-era AR. If I could use 62gr, that opens up more opportunities for ammo.

edit: credit to John for putting together all of this data in one place. Thanks!
__________________
I'm right about the metric system 3/4 of the time.
doofus47 is offline  
Old November 13, 2013, 12:27 PM   #7
kraigwy
Senior Member
 
Join Date: June 16, 2008
Location: Wyoming
Posts: 9,472
The best I can get M855 out of a 1:12 is at about 85-90 yards, then it goes south.

Velocity does matter. The test I posted was M16's, A1&A2s.

I have both and my rifles pretty much shot the same report as the test I posted.

Having said that, I have Remington M700 with a 1:12. It shoots the 62s much better then my SP1 (1:12). I'm sure that is do to velocity.

How ever I have a Remington Action Mann Device which is 1:7. Its only an 18 inch barrel yet it shoots the 62s much better then the M700 1:12 even with less velocity.

One must understand that Barrel Twist Guides, are just that, Guides, not all guns are the same.

What I take from John's charts, as well as the Army's, is that fast twist shoot light bullets better then slow twist shoot heavy bullets.
__________________
Kraig Stuart
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071
kraigwy is offline  
Old November 13, 2013, 12:35 PM   #8
Metal god
Senior Member
 
Join Date: April 10, 2012
Location: San Diego CA
Posts: 2,029
Do you have a link to the articles ? Couple things I'm noticing is all the charts above say 223 . As we know 223 does not have the same velocity as 5.56 . Did they test 5.56 loadings with the same 77gr and 80gr bullets . Just spit balling here but I would think you could get a 77 or 80gr bullet loaded to 5.56 specs to stabilize in a 1-12 twist better then the same bullets loaded to 223rem specs

Sooo , I wanted to make sure I was not wrong in my above statement/question . I went and looked at my Sierra book and now I'm more confused then ever . Comparing AR specs pg222 and 223 specs pg232 . How does the age old rule apply and be correct that 5.56 rounds are loaded to higher pressures then 223rem . Sierra is using all the same components for both loads and yet they load the 223 with heavier charges just about across the board .

More powder means more pressure , YES ? I also see the rounds really having the same velocity's if they were both shot from the same length barrel . The only difference I see is the twist rate . can or does the 1-7 create 10,000-ish more psi then a 1-12 and that's where the pressure difference between a 5.56 and the 223rem comes from ?

Every time I think I have a good understanding of something my reloading world gets turned upside down . I guess school is in session once again .
__________________
As of this date 8-18-14 at 6:42am I became a proud grandfather I guess I'm officially old
Metal god is offline  
Old November 13, 2013, 01:01 PM   #9
kraigwy
Senior Member
 
Join Date: June 16, 2008
Location: Wyoming
Posts: 9,472
We should take that to another post instead of clouding up John's post on barrel twist.

Different subject.
__________________
Kraig Stuart
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071
kraigwy is offline  
Old November 13, 2013, 11:51 PM   #10
JohnKSa
Staff
 
Join Date: February 12, 2001
Location: DFW Area
Posts: 18,409
Quote:
I'm having a hard time reconciling the two images, Kraigwy's comparison of M193 and M855 target impacts and JonnKSa's "223REM rifling vs accuracy by bullet weight" and other graphs of his that indicate that 1:12 should be fine with 62gr bullets.
There is a critical caveat in my post.
Quote:
Bullets made of solid copper (or gilding metal or bronze), or bullets with steel cores will be longer for a given weight since those metals are less dense than lead. Because of their additional length, they might not stabilize with the twists recommended for a conventional (copper-jacketed lead core) bullet of the same weight.
The 62 grain ammunition Kraigwy is referring to has a steel core.
Quote:
If I could use 62gr, that opens up more opportunities for ammo.
With a 20" barrel, and out to a couple hundred yards, you're probably fine with 62gr ammo as long as it uses conventional copper-jacketed lead bullets and not solid gilding metal/solid copper or steel core bullets.
Quote:
Do you have a link to the articles ?
No, the articles are not online. I entered the data by hand into a spreadsheet to make the plots. You can probably contact the two magazines in question and ask for back issues or article reprints.
Quote:
As we know 223 does not have the same velocity as 5.56.
The velocity difference due to caliber is almost certainly swamped by differences from one gun to another and IS certainly swamped by barrel length differences.
Quote:
More powder means more pressure...
All else being equal it does. There are other differences in the two cartridges, the main one being the throat length which can have a significant effect on pressure.

Here's a fairly thorough treatment of the .223 vs. 5.56 issue.

http://thefiringline.com/forums/showthread.php?t=530912
__________________
Did you know that there is a TEXAS State Rifle Association?
JohnKSa is offline  
Old November 14, 2013, 02:04 AM   #11
Metal god
Senior Member
 
Join Date: April 10, 2012
Location: San Diego CA
Posts: 2,029
Quote:
All else being equal it does. There are other differences in the two cartridges, the main one being the throat length which can have a significant effect on pressure.
My books ( Sierra , Hornady ) Sierra is loading with the same components and Hornady has different brass and maybe primers but both books say the 223 gets the same or heavier charges then the NATO round . With the NATO throat being longer I would have thought the NATO round would be able to take the heavier charge .

I'm not implying anything just looking at the numbers and want to understand . That's why I was asking if it's all about the twist and if that increases or decreases pressure . Maybe factory NATO ammo is hotter then what the books recommend to load .

Your right kraigwy I have all kinds of questions and or statements and I see how this thread would get derailed very fast . Sorry I'll stop
__________________
As of this date 8-18-14 at 6:42am I became a proud grandfather I guess I'm officially old

Last edited by Metal god; November 14, 2013 at 02:23 AM.
Metal god is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 06:04 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.08715 seconds with 8 queries