1/7 twist on all Colt's current rifles

[Tbat]

I was in a local gun shop today and asked about Colt AR15's. They produced one from behind the counter which I assumed was a Colt 6920, and they did not correct me on it when I called it that, however, I noted the barrel twist rate was 1/9, instead of 1/7, and was purported to not be chromed lined.

I thought all of Colt's offerings have been 1/7 twist barrels for some time and that all of their barrels were chromed lined except for the new Expanse models. So is this some gun shop shenanigans or did I miss a memo from Colt?

[donlapalma]

A quick Google shows that their 6721/AR15-A3 Tactical Carbine comes with a 1/9 barrel. Perhaps this is what you saw:

http://www.colt.com/Catalog/Law-Enforcement/Products/Colt-Tactical-Carbine#98018-technical-specifications

[boombotz401]

I've never seen a 6920 in a 1/9, must be another model


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[JC5188]

My relatively new 6920 has a 1/7. I believe you saw something else.


Sent from my iPhone using Tapatalk

[Tbat]

A quick Google shows that their 6721/AR15-A3 Tactical Carbine comes with a 1/9 barrel. Perhaps this is what you saw:

http://www.colt.com/Catalog/Law-Enforcement/Products/Colt-Tactical-Carbine#98018-technical-specifications

Thanks everyone for the quick replies. It must have been the model that donlapalma referenced. I had no idea that a 6721 model existed.

[Ernst]

I have one of them. It is the Colt AR-15 A3. The barrel is chrome lined.

The 1:9 twist gives you a better range of bullet weight options.

Some do not like the weight of it though, since it is a heavier barrel. The rifle weights exactly one pound more than the 6920s.

Frankly, when everyone is freaking out about how hard to find LE6920s are, and when I look at the prices for the ones that are being sold, I think the AR-15 A3 is Colt's little secret.

:)

[TF82]

The 1:9 twist gives you a better range of bullet weight options.


This is not exactly true. 1:9 may give you better performance with the very light bullets under 55 gr. if that's what you intend to shoot, but it is unlikely to stabilize the heavier bullets, especially in the 70 gr. and up loads. At one time I believe it was Molon who did an excellent write up showing that 1:7 is quite capable of handling a lot of light loads. On the other hand, he also did a precision evaluation of a Colt 16" 1:9 HBAR and it turned really in impressive results.
https://www.m4carbine.net/showthread.php?54472-Colt-6721/page2

[Iraqgunz]

A 1/7 gives you a wider range of practical ammo from 55-77gr. with good accuracy.


I have one of them. It is the Colt AR-15 A3. The barrel is chrome lined.

The 1:9 twist gives you a better range of bullet weight options.

Some do not like the weight of it though, since it is a heavier barrel. The rifle weights exactly one pound more than the 6920s.

Frankly, when everyone is freaking out about how hard to find LE6920s are, and when I look at the prices for the ones that are being sold, I think the AR-15 A3 is Colt's little secret.

:)

[T2C]

A 1/7 gives you a wider range of practical ammo from 55-77gr. with good accuracy.

Did the 6920 always have a 1/7 twist barrel? Was it 1/7 in the early 1990's?

[Ryno12]

Did the 6920 always have a 1/7 twist barrel? Was it 1/7 in the early 1990's?

I don't believe the 6920 existed in the early 1990's.

ETA: found this. According to Scottryan, it was introduced in 1999.

https://www.m4carbine.net/showthread.php?30333-COLT-MODEL-LE6920-HISTORY

[Clay34]

Check out the video about the 1 1/2 minute point: http://www.alloutdoor.com/2016/01/20/new-products-from-colt-at-the-2016-shot-show/ Colt Expanse???

I just ordered a Colt in a 1 in 8 twist by the way. It's Colt yes, but a separate company Colt Competition. I ordered the CRP-18 Pro Gen II. It's a precision gamer gun and there is little about it on the web. When I do a search I get a lot of information on the previous model but very little information on the Gen II not even on Colt Competition's web site. Waiting is already killing me since it won't be made until May or June.

[Molon]

Did the 6920 always have a 1/7 twist barrel? Was it 1/7 in the early 1990's?




Early Colt AR6920DC upper groups came with a 1:9" twist barrel. I owned a few of them back then.



https://app.box.com/shared/static/8pv70x7ml5afgadlt47aj2x8dznlaunx.jpg



...

[Molon]

The 1:9 twist gives you a better range of bullet weight options.






False.










I have one of them. It is the Colt AR-15 A3. . . The rifle weights exactly one pound more than the 6920s.





False.

The only significant difference between the 6721 and the 6920 is the barrel.

The stripped 6721 barrel weighs 2 pounds, 3.4 ounces. The stripped 6920 barrel weighs one pound, 12 ounces. That's a difference of only 7.4 ounces.



Colt 6721, 16" HBAR: 2 pounds, 3.4 ounces.



https://app.box.com/shared/static/3bnl8bdr23.jpg






Colt 6920: 1 pound, 12 ounces.


https://app.box.com/shared/static/j14x5puqrvltgj5qwwj718hhpasopkgd.jpg



...

[Molon]

On the other hand, he also did a precision evaluation of a Colt 16" 1:9 HBAR and it turned really in impressive results.
https://www.m4carbine.net/showthread.php?54472-Colt-6721/page2


The 6721 barrel produces better precision because of its heavier profile.



https://app.box.com/shared/static/zy0a61s0qrl0aui5rtk1bfctrg4fqg05.jpg










At one time I believe it was Molon who did an excellent write up showing that 1:7 is quite capable of handling a lot of light loads.





.......................









55 grain bullets are unstable/overstabilized/inaccurate/less-lethal when fired from an AR-15 with a 1:7” twist barrel.






By definition, an “unstable” bullet will have a gyroscopic stability factor of less than 1.0 at the muzzle. A typical 55 grain FMJ bullet will have a gyroscopic stability factor of approximately 4.27 when fired from a 20” barrel with a 1:7” twist.
4.27 is not less than 1.0.


The following demonstration compares the results of firing four 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist. The first barrel used in testing was 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721. All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using hand-loaded 55 grain Sierra MatchKings.

The second barrel used in testing was a 20” Colt HBAR, also with chrome lining, a NATO chamber and of course a 1:7” twist. I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and using hand-loaded 55 grain Sierra MatchKings. The longer barrel with the 1:7” twist was purposely chosen for the increased muzzle velocity coupled with the 1:7” twist.

Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. The barrels were free-floated during testing. The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Naturally, the wind conditions were monitored using a Wind Probe. The set-up was very similar to that pictured below.




http://www.box.net/shared/static/xo4duzdgtp.jpg




Four 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.

As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel. Those groups were also also over-layed on each other to form a 40-shot composite group; the results were nearly identical to those obtained from the 1:9” twist barrel. The composite group had a mean radius of 1.01”. The two composite groups are shown side by side for comparison.




http://www.box.net/shared/static/o03ufeured.jpg




The entire test as described above was also conducted using a second 16" chrome-lined, NATO chambered Colt barrel with a 1:9" twist, and a second 20" chrome-lined NATO chambered Colt HBAR with a 1:7" twist. The ammunition used in this test was Wolf 55 grain FMJ "Performance Ammunition." As before, four 10-shot groups fired from each barrel at 100 yards were over-layed on each other using RSI Shooting and just as before, the mean radii for these 40-shot composite groups were nearly identical.




http://www.box.net/shared/static/mzaeeq0v50.jpg




Testing performed by C.E. Harris at Aberdeen Proving Ground and later at Sturm-Ruger has shown that the “overstabilization” claim is largely nonsense. The testing showed that “overspinning” quality light-weight bullets from a fast twist barrel does not become an issue unless you have a gyroscopic stability factor greater than 5.0 (which would require something along the lines of a 1:6” twist barrel launching a 55 grain bullet at over 3500 fps) or unless firing at an angle greater than 85 degrees.

After the U.S. Military adopted the 1:7” twist for the M16A2, C.E. Harris did extensive testing comparing the accuracy of light-weight bullets fired from 1:10” twist barrels and 1:7” twist barrels using 52 grain Sierra MatchKings. The accuracy testing was done from 200 yards, (well into the downward slope of the trajectory where the Internet Commando claims that all manner of evil befalls the “overstabilzied” bullet), and the accuracy results from the two different twist barrels were also nearly identical.





Quality, modern lightweight bullets of copper-jacket/lead-core construction can shoot superbly from AR-15s with fast twist barrels. Typical 55 grain FMJ bullets do not fall into the quality category.



The 10-shot group pictured below was fired from a distance of 100 yards from a Noveske barreled AR-15 with a 1:7” twist using 55 grain BlitzKings.




http://www.box.net/shared/static/9p6kf1904l.jpg





For any Internet Commando’s in our viewing audience, the 3-shot group pictured below was fired from the same 1:7” twist barrel using 55 grain BlitzKings.




http://www.box.net/shared/static/choz3qrhxf.jpg




The next 10-shot group pictured was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.




http://www.box.net/shared/static/0fuxcv68qk.jpg




The group pictured below was fired from one of my Krieger barreled AR-15s with a 1:7.7" twist from a distance of 100 yards using Berger 55 grain HP bullets. The group has an extreme spread of 0.76".




https://app.box.com/shared/static/hntfrbgamo2drhgqkcqaezcxk2v8g86f.jpg





A 14.5" Colt M4A1 SOCOM barrel,with its NATO chamber, chrome lining and 1:7" twist can shoot quality 55 grain bullets quite well.




http://www.box.net/shared/static/r9jgrq14zn.jpg





Here's another example of just how well a 1:7" twist barrel can shoot light weight bullets. While the group pictured below was fired from a distance of only 50 yards, it's a 10-shot group fired from a chrome lined, NATO chambered Colt barrel with a 1:7" twist using 52 grain Sierra MatchKings.




http://www.box.net/shared/static/kras1x3uyy.jpg




....

[titsonritz]

^^^I think that should just about cover it. :agree: