An Accuracy Comparison of M855 When Fired From 1:9” Twist and 1:7” Twist Barrels.

[Molon]

An Accuracy Comparison of M855 When Fired From 1:9” Twist and 1:7” Twist Barrels.

https://app.box.com/shared/static/l25ne79v486ocd9j4hgr9nmv3qie0iya.jpg




This test will compare the accuracy (technically, precision) of M855, produced by Israel Military Industries (IMI), when fired from an AR-15 with a chrome-lined, NATO chambered barrel with a 1:9” twist and an AR-15 with a chrome-lined, NATO chambered barrel with a 1:7” twist. The IMI M855 is the singularly most accurate and consistent loading of all the M855 clones that I have tested to date.

IMI M855 is loaded with a 62 grain FMJ bullet with a cannelure. It also has a steel penetrator seated in the ogive portion of the projectile. This makes the projectile unusually long for its weight, as well as giving it a lower specific gravity. The ammunition is charged with "ball powder". The primers are sealed and crimped in placed. The bullet is also crimped in place and the case mouth is sealed with an asphalt sealant.




https://app.box.com/shared/static/ao96ov1knvrjw1182cni5wh0vewrqxtw.jpg




Chronograph data for the IMI M855 was obtained using an Oehler 35P with "proof screen" technology. All velocities listed are muzzle velocities as calculated from instrumental velocities using Oehler's Ballistic Explorer software program. All strings of fire consisted of 10 shots each.




https://app.box.com/shared/static/nzaeafh4dpq2nozl6gyrvugubk8nt3vc.jpg




This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, control-groups were fired from the barrels used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrels.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrels used in the evaluation were free-floated. The free-float handguard of the rifle rested in a Sinclair Windage Benchrest with the aid of a Sinclair fore-arm adaptor, while the stock of the rifle rested in a Protektor bunny-ear 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. Wind conditions on the shooting range were continuously monitored using a Wind Probe. All rounds were fired from the magazine. Each upper was fired using the same lower. The set-up was very similar to that pictured below.




https://app.box.com/shared/static/8ybmvvks8dyx1t1soslfzpxgah071370.jpg




The barrels used in this evaluation were both Colt HBARs with NATO chambers and chrome lining. The 1:7” twist barrel was 20” in length and the 1:9” twist barrel was 16” in length. When fired from the 16” barrel with a 1:9” twist, the M855 projectile will have a gyroscopic-stability-factor of approximately 1.24 and when fired from the 20” barrel with a 1:7” twist the gyroscopic-stability-factor will be approximately 2.07. I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates might have on the precision of the M855 ammunition.



Colt 16" HBAR

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



Colt 20" HBAR

https://app.box.com/shared/static/iwfsn6obd447c9dmxdhtg7yu4k5tic5y.jpg





Prior to the firing of the M855, control groups were fired from the test barrels using match-grade handloads seated with Sierra 55 grain BlitzKings. The 10-shot control group fired from the 1:7” twist barrel had an extreme spread of 1.17” and the 10-shot control group fired from the 1:9” twist barrel had an extreme spread of 0.89”.


Three 10-shot groups were fired from the upper with the 1:9” twist barrel in the manner described above. The extreme spreads for those groups measured:

2.72”
2.19”
2.24”

for a 10-shot group average of 2.38”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 0.76”.



In the same manner as above, three 10-shot groups were fired from the upper with the 1:7” twist barrel. The extreme spreads of those groups measured:

2.14”
3.01”
1.71”

for a 10-shot group average of 2.29”. As before, the three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for this composite group was 0.68”.




….

[556BlackRifle]

A very interesting and informative post as usual. Thanks for taking the time to do all the work and share it with us here.

[Toddler]

Thanks for posting the results.

[TSD422]

Super informative post. Thanks for the info!

[Dionysusigma]

What, if any, factors would the differing barrel lengths have on the results?

[BatteryOperated]

Great job! Thank You for your efforts and posting your findings.

[3 AE]

Basically it was a wash with this lot of IMI ammo. I'm curious what a 16" with a 1:7" Colt HBAR would have achieved with the same lot. Or even a 16" with a 1:7" Govt. M4 profile barrel to compare with these results using M855. Here's a link to Molon's accuracy test of a 14.5" SOCOM. Also shows results of two 16" M-4 profile barrels. Though match grade ammo was used in the testing.

https://www.m4carbine.net/showthread.php?59364-The-Colt-M4A1-SOCOM-Barrel

Thanks Molon for continuing to keep M4Carbine.net on course with informative content. :thank_you2:

Some more data to peruse from Molon.

https://www.m4carbine.net/showthread.php?61263-Accuracy-Evaluation-of-Six-Different-Noveske-Barrels

[uniform64]

Nice! Thank You

[vicious_cb]

Basically it was a wash with this lot of IMI ammo. I'm curious what a 16" with a 1:7" Colt HBAR would have achieved with the same lot. Or even a 16" with a 1:7" Govt. M4 profile barrel to compare with these results using M855. Here's a link to Molon's accuracy test of a 14.5" SOCOM. Also shows results of two 16" M-4 profile barrels. Though match grade ammo was used in the testing.

https://www.m4carbine.net/showthread.php?59364-The-Colt-M4A1-SOCOM-Barrel

Thanks Molon for continuing to keep M4Carbine.net on course with informative content. :thank_you2:

Some more data to peruse from Molon.

https://www.m4carbine.net/showthread.php?61263-Accuracy-Evaluation-of-Six-Different-Noveske-Barrels

How is this "a wash"? The point of this test was to show that people who keep making excuses for their subpar barrels dont have a leg to stand on. There is absolutely zero point to having a 1:9 twist barrel in a fighting gun.

[BSmith]

How is this "a wash"? The point of this test was to show that people who keep making excuses for their subpar barrels dont have a leg to stand on. There is absolutely zero point to having a 1:9 twist barrel in a fighting gun.

If they are never going to shoot heavy bullets, who cares?

[vicious_cb]

If they are never going to shoot heavy bullets, who cares?

Because these people can see the future right?

[BSmith]

Because these people can see the future right?

Well then, I have quite a few things I need to change in my life.

[T2C]

This is good information Molon. Your differences in muzzle velocity based on barrel length mirror what I have seen during testing.

Have you done this comparison of twist rates with M193 and the same rifles you used in this test?

[BillyJack556]

This is good information Molon. Your differences in muzzle velocity based on barrel length mirror what I have seen during testing.

Have you done this comparison of twist rates with M193 and the same rifles you used in this test?
I would like to see those results also.

[Molon]

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 3.7 when fired from a 20” barrel with a 1:7” twist. 3.7 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; a chrome-lined, NATO chambered barrel with a 1:9” twist, and a chrome-lined, NATO chambered 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. 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. The longer barrel with the 1:7” twist was purposely chosen for the increased muzzle velocity coupled with the 1:7” twist. Both barrels had free-float handguards.

Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. 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




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 (40 to 55 grain) of typical copper-jacket/lead-core construction can shoot superbly from fast twist barrels. Typical 55 FMJ bullets do not fall into the quality category.


The group pictured below was fired from a 1:7" twist Noveske barrel using 40 grain V-MAX bullets.


http://www.box.net/shared/static/j598a57fgb.jpg




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.


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




The 3-shot group pictured below was fired from the same 1:7” twist barrel for the Internet Commandos in our viewing audience.

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





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




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




A 1:7” twist rate does not have a negative effect on the terminal ballistic properties of M193 and M855. From Dr. G.K. Roberts . . .

"The U.S. Army Wound Ballistic Research Laboratory conducted terminal performance testing using 5.56 mm 55 gr M193 FMJ ammunition fired in 20” barrels of 1/14, 1/12, 1/9, and 1/7 twist rates. No difference in terminal performance was noted between shots made with the different twists. Similar testing was conducted with 5.56 mm 62 gr M855 FMJ ammunition fired in 1/9 and 1/7 twist barrels. Again, no difference in terminal performance was noted."


….

[JS-Maine]

Unreal...your posts are ridiculously enjoyable. Thanks for another ace.

[Hank6046]

Awesome post, very interesting. You answer those questions that I talk to my buddies and I tend to only speculate about. Thanks for the interesting read.

[556BlackRifle]

The post that keeps getting better. Thanks Molon. :)

[HKGuns]

Thanks for posting. It would be interesting to see a similar test done at say 200-400 yards with an extrapolation of the 100 yard data to see if it holds up.

[lysander]

How is this "a wash"? The point of this test was to show that people who keep making excuses for their subpar barrels dont have a leg to stand on. There is absolutely zero point to having a 1:9 twist barrel in a fighting gun.
I think it shows just the opposite. That there is no real loss of accuracy with a 1:9 twist barrel and the M855 ammunition.

An increase in 0.08" (the thickness of a comic book) in the mean radius over 100 yards is unnoticeable if you are using a 2 MOA red dot, and, if you were using iron sights, this increase would be lost in your aiming errors.

As to the 16" vs 20", other tests (http://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/) have shown there is little loss of accuracy when going from a longer to a shorter barrel, less than .1" on average at 100 yards on average and almost zero for 18" to 16" barrels.

[Alpha-17]

I think it shows just the opposite. That there is no real loss of accuracy with a 1:9 twist barrel and the M855 ammunition.


Nor should there have been. The argument in favor of 1:9 twist barrels usually is that they are more accurate with the 40-69gr stuff than the 1:7 twist barrels. This showed that was not in fact true with 62gr M855. Best case argument for the 1:9 twist is that it should might handle the lighter bullets better, and it handles the mid weight almost as good, while 1:7 does handle the mid weight better, and opens the user up to better, heavier bullets.

To each their own, I just like the heavier bullets enough to not be interested in any 1:9 twist barrels on any of my guns.

[lysander]

Best case argument for the 1:9 twist is that it should might handle the lighter bullets better...
But, post #15 shows that 1:7 are easily capable of very good accuracy with lighter bullets.

So, there seems to be little difference between the twist rates unless you plan on using 70 grain bullets or longer.

[T2C]

Thank you Molon, With a Mean Radius of 1.08", I would guess the M193 will shoot around 3" at 100 yards when fired through a 1:9 twist barrel, which has been my experience. Oddly enough, when I fired M193 through my Colt HBAR(s) with 20" 1:7 twist barrel(s), it would not group as well as when I fired it through a 16" barrel with either a 1:7 or 1:9 twist rate.

I agree with what was posted concerning terminal ballistics. The issue some of us had with faster twist rates with lighter bullets was when punching paper with off the shelf 55g FMJ ammunition. Box store 62g shot a lot better out of my HBAR(s) than 55g. With quality bullets, bullet weight made a negligible difference in accuracy when developing match loads for shooting reduced course matches at 300 yards and closer.

I think where the debate in accuracy in different twist rate barrels starts to get heated is when tactical shooters discuss the topic with people who are trying to develop 1/2 MOA ammunition for high power and bench rest competition. Most people do not shoot well enough to tell the difference.

Good thread.

[Alpha-17]

But, post #15 shows that 1:7 are easily capable of very good accuracy with lighter bullets.

So, there seems to be little difference between the twist rates unless you plan on using 70 grain bullets or longer.

I was referring to the varmint bullets in the 40gr range. I don't personally have any use for either the bullets or the 1:9 twist barrels, am only repeating the arguments I've seen online.

[lysander]

I was referring to the varmint bullets in the 40gr range. I don't personally have any use for either the bullets or the 1:9 twist barrels, am only repeating the arguments I've seen online.


The group pictured below was fired from a 1:7" twist Noveske barrel using 40 grain V-MAX bullets.
http://www.box.net/shared/static/j598a57fgb.jpg

[MegademiC]

The only issue I've ever heard with 1/7 is that very light bullets (30 - 35 gr?)with very thin jackets going very fast can fragment a few feet from the barrel. Outside of niche applications, 1/7, 1/8 is the way to go.

As ussual, great post molon.

[C4IGrant]

Good thread! I have had great experience with V-Max 55gr out of my 1/7 twist barrels out to 100yds. What would be interesting is to continue on with this test out to 200yds. I am curious if the 1/9 twist will continue to perform the same with the M855.




C4

[Molon]

I have had great experience with V-Max 55gr out of my 1/7 twist barrels out to 100yds.




As you've discovered, the 55 grain V-MAX shoots very well from an AR-15. You might also want to try the newer Hornady 53 grain V-MAX Superformance load if you use 20" or longer barrels.



http://www.box.net/shared/static/sdpjt3h36v.jpg




http://www.box.net/shared/static/gz5c0rj80f.jpg




The 53 grain V-MAX is shown on the left compared to a 52 grain A-MAX on the right.

http://www.box.net/shared/static/co0sa2tsdk.jpg



....

[C4IGrant]

Thanks. I don't own a 20" barrel (unless you count a 16" barrel with a can on it). :)




C4

[SkiDevil]

Great information Molon. Thanks for sharing with us.

I will point people to your findings when they say, "you can't shoot light bullets in a 1/7 barrel". I have found my Noveske barrels to shoot light grain bullets well too.

It is good to see you back again. :)

[T2C]

In my opinion the 55g V-Max cartridge is the gold standard. Usually, if a rifle won't shoot the V-Max well, it won't shoot anything well.

[Molon]

With a Mean Radius of 1.08", I would guess the M193 will shoot around 3" at 100 yards when fired through a 1:9 twist barrel, which has been my experience. Oddly enough, when I fired M193 through my Colt HBAR(s) with 20" 1:7 twist barrel(s), it would not group as well as when I fired it through a 16" barrel with either a 1:7 or 1:9 twist rate.



Three 10-shot groups from a 16" Colt HBAR with a 1:9" twist . . .

http://www.box.net/shared/static/e4ckmi2y36.jpg




1:7" twist versus 1:9" twist with 55 grain FMJ Ammunition

Using the Prvi M193 ammunition, I did an accuracy comparison firing the 55 grain FMJ load from both a 16 inch, 1:9” twist Colt HBAR and a 20 inch, 1:7” twist Colt HBAR. Four 10-shot groups were fired from each barrel from a bench-rest at a distance of 100 yards. The groups from each barrel were over-layed to form 40-shot composite groups. The mean radii of the composite groups were nearly identical.


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



....

[556BlackRifle]

55gr V-Max is my favorite load. Out of a my Noveske 16" 1/7 it's accurate. (1 - 2 MOA) Out of my Shaw 1/9 it's phenomenal. (0.85 - 1.25 all day long.) :)

[Molon]

Thanks. I don't own a 20" barrel (unless you count a 16" barrel with a can on it). :)



If you reload, the 53 grain V-MAX is also available as a component.


https://app.box.com/shared/static/81upcj2x66p33v153e1pohpjel5vn0h2.jpg

[bernieb90]

I saw a very interesting article in American Rifleman that claimed that both M855 and M855A1 were more accurate in the 1/9 twist barrels than 1/7.

http://www.americanrifleman.org/articles/2014/5/21/testing-the-army-s-m855a1-standard-ball-cartridge/


Accuracy cannot be assessed without addressing the rifle barrels’ twist-rates. In the early 1980s the M855’s 62-grain bullet was developed for the M249 Squad Automatic Weapon (SAW). For purposes of interoperability, the same load was adopted as the M16A2 rifle’s standard ball as well. A February 1986 U.S. Army study noted that the M855’s bullet required a “1:9 twist [which] would be more appropriate for the M16A2 rifle, improving accuracy and reliability.” Multiple studies confirmed the 1:9-inch twist requirement.

But then a problem arose. The U.S. military’s standard M856 5.56 mm tracer round was longer, heavier (63.7 grains) and slower than the M855 ball, and simply would not stabilize with a 1:9-inch twist barrel. Thus, despite it doubling M855 group sizes, the M16A2 (and later, the M4) specified a 1:7-inch rate-of-twist barrel to stabilize the tracer round. It remains so to this day. Therefore, M855A1 was test-fired with both 1:7- and 1:9-inch twist barrels, and it was verified that this new cartridge is consistently more accurate in the latter barrels-as was its predecessor.

The M855A1’s developers have described it as yielding “match-like” accuracy, which most rifle shooters would define as one minute-of-angle (m.o.a.), or groups measuring no more than 1 inch at 100 yards. While the new ammunition has proved more accurate than the green-tipped load it replaced, testing did not yield match-like accuracy, especially in the standard 1:7-inch twist-rate found in today’s M4s and M16s. At 100 yards, the best group with a 1:7-inch barrel was 1.62 inches (1.6 m.o.a.). At 300 yards. it similarly fired 1.6 m.o.a. (4.9 inches) and widened to 1.8 m.o.a. (7.5 inches) at 400 yards. At these same distances, firing the M855A1 through a 1:9-inch twist barrel reduced group sizes by approximately half.

I am still not sure how the twist rate would make such a huge difference as they claim. I am thinking they are trying to cover up poor accuracy by blaming it on twist rate differences.

[HansTheHobbit]

I would expect a slight improvement to be due to the increased barrel length in the 1:7. The 1:7 might cut the wind a bit better at range, I'm guessing it would resist wobbling longer, but I wouldn't expect much difference between 1:9 and 1:7 at normal ranges in the same length barrel.

...with 62 grain I mean.

[MegademiC]

I saw a very interesting article in American Rifleman that claimed that both M855 and M855A1 were more accurate in the 1/9 twist barrels than 1/7.

http://www.americanrifleman.org/articles/2014/5/21/testing-the-army-s-m855a1-standard-ball-cartridge/



I am still not sure how the twist rate would make such a huge difference as they claim. I am thinking they are trying to cover up poor accuracy by blaming it on twist rate differences.

I would think that the barrels were not of the same standard. What is the manufacture, profile, and round count of each? I'd be curious.

Also how many rounds? 3 shot groups? We all know about those.

[HansTheHobbit]

I would think that the barrels were not of the same standard. What is the manufacture, profile, and round count of each? I'd be curious.

Also how many rounds? 3 shot groups? We all know about those.

It's the Army. 3 was all they could afford... :laugh:

They did however spend 1.3 billion to have admins compute the data and prepare a slideshow.

[MegademiC]

It's the Army. 3 was all they could afford... :laugh:

They did however spend 1.3 billion to have admins compute the data and prepare a slideshow.

****ing government "science".

[giggity]

sweet comparison.. thanks! didn't know IMI was such a good load but basically everything from Israel is of fine quality so I guess I can see why.

[T2C]

sweet comparison.. thanks! didn't know IMI was such a good load but basically everything from Israel is of fine quality so I guess I can see why.

I've fired good groups with Malaysian ball in both 5.56mm and 7.62x51. Too bad the supply has dried up. I wish the .30 caliber surplus was still readily available, because it shoots sub MOA at 300 yards.

[steyrman13]

I've fired good groups with Malaysian ball in both 5.56mm and 7.62x51. Too bad the supply has dried up. I wish the .30 caliber surplus was still readily available, because it shoots sub MOA at 300 yards.

Did you not find the Malaysion 5.56 to be too hot? I was blowing primers with the lots that I have had handed down to me. Probably made in the 80s-90s.

[daddyusmaximus]

Thanks for the detailed post. I am glad I chose a 1/8 twist barrel for my 16"AR. It is a very accurate gun. I do think that the twist rate is a choice you make when your requirement is for a particular round. Like the military going to 1/7 to stabilize the new tracer. This is only a general rule of thumb as two identical guns from the same maker can like a different round. This is why load development is so important for precision shooters. To me the overall quality of the barrel is more important. I would take a 1/8 or 1/9 barrel of good quality over a run of the mill 1/7 any day. In fact, my SBR had a progressive twist 1/9 barrel with polygonal rifling and is plenty accurate with m855, though this round is not my first choice anyway. It can shoot m193 in sub MOA groups. Twist does matter when you go way heavier. The little SBR doesn't like the Hornady 75gr TAP that the 16" gun groups well with. (at SBR engagement distances it doesn't matter)

[T2C]

Did you not find the Malaysion 5.56 to be too hot? I was blowing primers with the lots that I have had handed down to me. Probably made in the 80s-90s.


It chronographed right at 3,240 fps, which was faster than most other M193 ball I shot. I shot it out of RRA match rifles when practicing at reduced distance (200 yards) for High Power matches. I fired several thousand rounds and never had a popped primer. The RRA match rifles have a .223 Wylde chamber and that may be why I never had a popped primer. I never fired it through a 5.56mm chamber.

[Molon]

It can shoot m193 in sub MOA groups.





Wolf Gold 55 grain FMJ



https://app.box.com/shared/static/7jirxh9zv1kyzunget5jzlg44ue3gkr1.jpg




When most shooters hear the phrase “Wolf ammunition,” what usually comes to mind is steel-cased rounds loaded with bi-metal jacketed bullets. Fortunately, the 55 grain FMJ “Wolf Gold” ammunition that is manufactured in Taiwan does not fit this description.

The Wolf Gold ammunition reviewed for this report uses brass cases with the annealing iris still visible and is loaded with typical copper jacketed/lead core bullets. The 55 grain projectile has a cannelure and there is a collet crimp at the case mouth. The case mouth is also sealed with asphalt sealant. The brass case has crimped and sealed boxer primers and the round is charged with ball powder.




https://app.box.com/shared/static/okxno5wuhs02rcsluwylnp7h8093wgyj.jpg




https://app.box.com/shared/static/ve5lm9pvar8cxmd8um7ovt858b3jx9iv.jpg




https://app.box.com/shared/static/6cnlau4zjuvp73c9o5b69vpknbipocyp.jpg






When most shooters hear the phrase “55 grain FMJ,” what usually comes to mind is M193 ammunition. The velocity specification for M193 as cited in MIL-C-9963F states:

The average velocity of the sample cartridges, conditioned at 72 degrees, plus or minus 2 degrees Fahrenheit (F), shall be 3165 feet per second (ft/sec), plus or minus 40 ft/sec, at 75 feet from the muzzle of the weapon. The standard deviation of the velocities shall not exceed 40 ft/sec.


The specification is for a 20” barrel. Depending on multiple variables, this velocity specification equates to a muzzle velocity of approximately 3270 FPS, plus or minus 40 FPS. I chronographed the Wolf Gold 55 grain FMJ ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel.



http://www.box.net/shared/static/h8daj1jhf1.jpg



Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. The Oehler 35P chronograph is actually two chronographs in one package that takes two separate chronograph readings for each shot and then has its onboard computer analyze the data to determine if there is any statistically significant difference between the two readings. If there is, the chronograph “flags” the shot to let you know that the data is invalid. There was no invalid data flagged during this testing.

The velocity stated below is the muzzle velocity as calculated from the instrumental velocity using Oehler’s Ballistic Explorer software program. The string of fire consisted of 10 rounds over the chronograph.



http://www.box.net/shared/static/52xzjapv7i.jpg




http://www.box.net/shared/static/q3lpmdumpm.jpg




Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release. Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.

The muzzle velocity for the 10-shot string of the Wolf Gold 55 grain FMJ ammunition was 3213 FPS with a standard deviation of 25 FPS. For comparison, IMI M193 had a muzzle velocity of 3274 FPS when fired from the same barrel, with a standard deviation of 18 FPS.




http://www.box.net/shared/static/lku6pn9aym.jpg



Atmospheric conditions.

Temperature: 77 degrees F
Humidity: 40%
Barometric pressure: 30.12 inches of Hg
Elevation: 950 feet above sea level



The accuracy specification for M193 cited in MIL-C-9963F is as follows:

The average of the mean radii of all targets of the sample cartridges, fired at 200 yards, shall not exceed 2.0 inches.

These averages are from 10-shot groups fired from machine rested, bolt-actioned test barrels, such as the ones pictured below. All things being equal (which of course they seldom are) this specification equates to a mean radius of 1 inch at 100 yards for 10-shot groups.



http://www.box.net/shared/static/akn05ro96d.jpg




http://www.box.net/shared/static/vs86o5rcf9.jpg






I conducted an accuracy (technically, precision) evaluation of the Wolf Gold 55 grain FMJ ammunition following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear 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. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.



https://app.box.com/shared/static/2hex4netcnq7qqagacf8cy14hvdk36q8.jpg





The Wind Probe.

https://app.box.com/shared/static/lkg47ptc04.jpg




The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel. The barrel has a 223 Wylde chamber with a 1:8” twist.

Prior to firing the Wolf Gold ammunition, I fired a 10-shot control group using match-grade hand-loads topped with the Sierra 55 grain BlitzKing. That group had an extreme spread of 0.78”.




https://app.box.com/shared/static/k0ozty7a9oje1zpni59eg9yc43s8z8c4.jpg




Next, three 10-shot groups of the Wolf Gold were fired in a row with the resulting extreme spreads:

2.13”
2.60”
2.44”

for a 10-shot group average extreme spread of 2.39”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the 30-shot composite group was 0.76”.




The smallest 10-shot group.

https://app.box.com/shared/static/bkgrs45juppky9ctdfhx4f0lhi0b39u8.jpg





The 30-shot composite group.

https://app.box.com/shared/static/muokg675ygjz5n0u9ugupp1k6jlzvep2.jpg




….

[Molon]

Attack of the (M193) Clones



clone: one that appears to be a copy of an original form.

Genuine M193 must be tested for and pass all of the specifications laid out in the mil-spec, MIL-C-9963. The required areas of testing included in MIL-C-9963 range from velocity, accuracy, chamber pressure and port pressure to waterproofing, temperature stability, bullet extraction, case hardness, fouling and more.

Genuine US Military M193 can no longer be sold to civilians, thanks to the Clinton Administration. The ammunition that is sold on the commercial market with some form of “M193” in its nomenclature is often referred to as an “M193 clone” because it “appears to be a copy” of genuine M193, but we generally have no idea what specifications of MIL-C-9963 that this ammunition has passed, or has even been tested for.

M193 is loaded with a 55 grain FMJ bullet with a cannelure. The bullet itself, must meet required specifications to be used in genuine M193. For example, the specification for the thickness of the gilding metal jacket of the bullet is 0.021" with a tolerance of - 0.002". For comparison, the jacket of Hornady’s 55 grain FMJ bullet has a thickness of approximately 0.028”. Jacket thickness can have a significant effect on terminal ballistic properties, particularly that of fragmentation. Even the composition of the copper alloy used for the jacket and the lead used for the slug must meet mil-spec requirements for genuine M193.

Genuine US Military M193 can only be charged with powder that has been specifically approved by the US Military for use in this cartridge. If the ammunition in question is not loaded with one of the approved powders, it is not genuine M193 and naturally we have no way of determining what powder was used in a load simply by visual inspection.

Genuine M193 will have the annealing iris visible on the shoulder and neck portion of the case. It will also will have crimped and sealed primers. Genuine M193 has a crimped case mouth along with sealant at the case mouth.


The velocity specification for M193 as cited in MIL-C-9963F states:

The average velocity of the sample cartridges, conditioned at 72 degrees, plus or minus 2 degrees Fahrenheit (F), shall be 3165 feet per second (ft/sec), plus or minus 40 ft/sec, at 78 feet from the muzzle of the weapon. The standard deviation of the velocities shall not exceed 40 ft/sec.

The specification is for a 20” barrel. Depending on multiple variables, this velocity specification equates to a muzzle velocity of approximately 3270 ft/sec, plus or minus 40 ft/sec.

I chronographed four different M193 clones back-to-back for comparison. All four of these loads are currently available on the commercial market (at the time of this writing). These loads were fired from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel. The four loads are listed below:

IMI M193
American Eagle Tactical M193
Privi Partizan (PPU) M193
Winchester Q3131A1.



http://www.box.net/shared/static/g6jtfsjkou.jpg



http://www.box.net/shared/static/9e7m4fpm2n.jpg



M16A2 barrel.
http://www.box.net/shared/static/czdlerd8y1.jpg


Chronographing of the M193 clones was conducted using an Oehler 35-P chronograph with “proof screen” technology. All velocities listed below are muzzle velocities as calculated from the instrumental velocities using Oehler’s Ballistic Explorer software program. All strings of fire consisted of 10 rounds each.


http://www.box.net/shared/static/52xzjapv7i.jpg


http://www.box.net/shared/static/q3lpmdumpm.jpg



Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release. Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.


http://www.box.net/shared/static/lku6pn9aym.jpg


Atmospheric conditions.

Temperature: 79 degrees F
Humidity: 42%
Barometric pressure: 30.19 inches of Hg
Elevation: 950 feet above sea level


http://www.box.net/shared/static/nh3vk2komi.jpg


Continued in the next post . . .

[Molon]

The accuracy specification for M193 cited in MIL-C-9963F is as follows:

The average of the mean radii of all targets of the sample cartridges, fired at 200 yards, shall not exceed 2.0 inches.

These averages are from 10-shot groups fired from machine rested, bolt-actioned test barrels, such as the ones pictured below. All things being equal (which of course they seldom are) this specification equates to a mean radius of 1 inch at 100 yards.

(For those of you not familiar with the mean radius, see post #4 below.)




http://www.box.net/shared/static/vs86o5rcf9.jpg



I conducted an accuracy (technically, precision) evaluation of the same four M193 clones that were chronographed above, following my usual protocols. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots). The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Pictures of the fired shot-groups will be posted for documentation.


All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear 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. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.



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


The Wind Probe.
http://www.box.net/shared/static/lkg47ptc04.jpg




The test vehicle for this evaluation was a 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721 carbine. This barrel was free-floated with a 10” LaRue free-float handguard. I specifically choose to evaluate the accuracy of this ammunition using an AR-15 with a chrome-lined, NATO chambered barrel, as this is the type of barrel that is most commonly used to fire this type of ammunition.

It is possible to obtain better accuracy with mil-spec/NATO pressure loads when fired from an AR-15 that has a stainless steel match-grade barrel with a hybrid chamber such as the Noveske NMmod0 chamber or the Wylde chamber for examples. You're not going to make a silk purse out of a sow’s ear doing this, but I’ve previously experienced up to a 20% improvement in accuracy by doing so.





http://www.box.net/shared/static/9jkbf66dd6.jpg



http://www.box.net/shared/static/3bnl8bdr23.jpg


The 16” Colt HBAR is one of the most accurate “off the shelf” chrome-lined, NATO chambered AR-15 barrels that I’ve evaluated. Three 10-shot groups fired from this barrel from a distance of 100 yards using match-grade hand-loads topped with Sierra 52 grain MatchKings had extreme spreads of:


0.85”
1.14”
0.88”

for a 10-shot group average extreme spread of 0.96”. Over-laying the three 10-shot groups on each other using RSI Shooting Lab software produced a 30-shot composite target with a mean radius of 0.32”.




IMI M193

http://www.box.net/shared/static/binxmdj27l.jpg



Three 10-shot groups of the IMI M193 were fired in a row from a distance of 100 yards from the Colt 16” HBAR. Those three groups had extreme spreads of:

2.83”
2.77”
2.80”

for a 10-shot group average extreme spread of 2.80”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The composite group had a mean radius of 0.97”.


The smallest 10-shot group.

http://www.box.net/shared/static/jqz9iexntb.jpg




The 30-shot composite group.


http://www.box.net/shared/static/osl5r38t2u.jpg




American Eagle Tactical XM193

http://www.box.net/shared/static/5oigjl4jts.jpg


Three 10-shot groups of the American Eagle Tactical XM193 fired in a row had extreme spreads of:

3.01”
3.25”
3.57”

For a 10-shot group average of 3.27”. The 30-shot composite group had a mean radius of 0.98”.


The smallest 10-shot group.

http://www.box.net/shared/static/41x28np8kb.jpg



The 30-shot composite group.


http://www.box.net/shared/static/my2ctihg0m.jpg




Prvi Partizan M193

http://www.box.net/shared/static/a1azuheh16.jpg

Three 10-shot groups of the Priv Partizan M193 were fired in a row from a distance of 100 yards. The groups had extreme spreads of:

2.72”
3.89”
3.74”

for a 10-shot group average extreme spread of 3.45”. All three of these groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 1.01”.


The smallest 10-shot group of PPU M193

http://www.box.net/shared/static/fynap95fhq.jpg



The 30-shot composite group.

http://www.box.net/shared/static/64hrapyyj9.jpg




Winchester Q3131A1

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



Three 10-shot groups of the Winchester Q3131A1 load were fired in a row. The extreme spreads of those groups measured:

2.95”
3.73”
3.35”

for a 10-shot average extreme spread of 3.34”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 1.05”.


The smallest 10-shot group.

http://www.box.net/shared/static/k56ny29u1q.jpg



The 30-shot composite group.

http://www.box.net/shared/static/pl19x6ayp9.jpg





Here is a summary of the results of the accuracy evaluation of the four M193 clones.

http://www.box.net/shared/static/e4ckmi2y36.jpg



.....



1:7" twist versus 1:9" twist with 55 grain FMJ Ammunition

Using the Prvi M193 ammunition, I did an accuracy comparison firing the 55 grain FMJ load from both a 1:9” twist Colt HBAR and a 1:7” twist Colt HBAR. Four 10-shot groups were fired from each barrel from a bench-rest at a distance of 100 yards. The groups from each barrel were over-layed to form 40-shot composite groups. The mean radii of the composite groups were nearly identical.


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



....

[Molon]

PMC 5.56mm 62 Grain X-TAC Ammunition


https://app.box.com/shared/static/040no6g34e54yjxuvlmdheqkbniuy4ck.jpg




PMC’s 62 grain X-TAC ammunition is loaded in brass cases that have the annealing iris still visible. The 62 grain projectile has a copper jacket construction with a lead core and a steel insert in the ogive. The tip of the bullet is painted green. The case mouth is taper crimped into the cannelure of the bullet and the case-mouth is sealed with asphalt sealant.




https://app.box.com/shared/static/p22da5k1ethla3jsayott87wkrnfnc5h.jpg




https://app.box.com/shared/static/a121ro4si3jg9cpf4jl4lqq19jgm399g.jpg





The boxer primers are sealed and crimped and the load is charged with “ball” powder.




https://app.box.com/shared/static/0klbaviozk9wa1vjq5kb7tfz7udcnjoj.jpg




(The individual squares in the red grid below are 1/10th of an inch.)

https://app.box.com/shared/static/izmvzhv9hpt9zx2u0230paxjutf2utoq.jpg




After reading the above description of this PMC ammunition, some of you might be thinking, “I wonder how this ammunition compares to M855?” So, let’s compare!


The US mil-spec for M855 (MIL-C-63989C [Amendment 4]) states that the average velocity of the cartridges “shall be 3,020 feet per second (fps) plus or minus 40 fps at 78 feet from the muzzle of the weapon. The standard deviation of the velocity shall not exceed 40 fps.” This specification is for a 20” barrel and depending upon variables equates to a muzzle velocity of approximately 3105 FPS (plus or minus 40 FPS.)

As an aside, after reading the above specification, some of you may be wondering, “Why 78 feet from the muzzle?” The answer to that question is that this specification is simply an historical hold-over from the days when “circuit” chronographs (e.g. Le Boulenge Chronograph and the Aberdeen Chronograph) were used at Aberdeen Proving Ground, Frankford Arsenal and Springfield Armory. These types of chronographs required a significant distance between their first and second screens to produce accurate results.

As an example, when using the Boulenge Chronograph, the first screen of the chronograph was placed 3 feet in front of the muzzle and the second screen was placed 150 feet beyond the first screen. For those of you who might not be aware of the following fact; chronographs determine the velocity of the bullet at a point that is midway between the first and the second screen (i.e. not at the location of the first screen). Therefore, with the above spacing, the velocity of the bullet is determined for a point that is 75 feet from the first screen. So, add the three feet (from the muzzle to the first screen) to the 75 feet (the midway point of the screens) to obtain the “78 feet from the muzzle” distance.



https://app.box.com/shared/static/sj2isxyjw0iqtl0e1mcybqcg1g6hvaa8.jpg




https://app.box.com/shared/static/pj1xtbym3vnov134v10uaa87x5q0ro00.jpg





I chronographed the PMC 62 grain X-TAC ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel.




http://www.box.net/shared/static/h8daj1jhf1.jpg




Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. The Oehler 35P chronograph is actually two chronographs in one package that takes two separate chronograph readings for each shot and then has its onboard computer analyze the data to determine if there is any statistically significant difference between the two readings. If there is a difference, the chronograph “flags” the shot to let you know that the data is invalid. There was no invalid data flagged during this testing.

The velocity stated below is the muzzle velocity as calculated from the instrumental velocity using Oehler’s Ballistic Explorer software program. The string of fire consisted of 10 rounds over the chronograph.




https://app.box.com/shared/static/qecrizgcgxyzqztvq5xvb9gczasq71q3.jpg




https://app.box.com/shared/static/psjsdukng1c4p5efyw096kuka7p2aliu.jpg




Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release. Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.




https://app.box.com/shared/static/rwruh372al3yh9kafscx370ewe74e6el.jpg




Atmospheric conditions

Temperature: 78 degrees F
Humidity: 54%
Barometric pressure: 29.99 inches of Hg
Elevation: 950 feet above sea level


The muzzle velocity for the 10-shot string of the PMC 62 grain X-TAC ammunition fired from the 20” Colt barrel was 3073 FPS with a standard deviation of 14 FPS and a coefficient of variation of 0.46%. For comparison, IMI M855 chronographed from the same 20” Colt barrel had a muzzle velocity of 3110 FPS with a standard deviation of 21 FPS and a coefficient of variation of 0.68%.

For those of you who might not be familiar with the coefficient of variation (CV), it is the standard deviation, divided by the mean (average) muzzle velocity and then multiplied by 100 and expressed as a percentage. It allows for the comparison of the uniformity of velocity between loads in different velocity spectrums; e.g. 77 grain loads running around 2,650 fps compared to 55 grain loads running around 3,250 fps.

For comparison, the US mil-spec for M855 allows for a coefficient of variation of up to approximately 1.3%, while one of my best 77 grain OTM hand-loads, with a muzzle velocity of 2639 PFS and a standard deviation of 4 FPS, has a coefficient of variation of 0.15%.




https://app.box.com/shared/static/lz3su91r4ps75es4s3q97vpm1pdlri73.jpg




….





The accuracy specification from the US mil-spec for M855 (MIL-C-63989C) states that the average vertical standard deviation and the average horizontal standard deviation shall be “no greater than 1.8 inches at 200 yards using an indoor range.” * The accuracy testing is conducted using machine rested, bolt-action, heavy test barrels. All other things being equal (which of course they seldom are) this accuracy specification equates to an average vertical standard deviation and an average horizontal standard deviation of 0.9 inches at 100 yards (the distance at which I evaluated the accuracy of the PMC 62 grain X-TAC ammunition.)


I conducted an accuracy (technically, precision) evaluation of the PMC 62 grain X-TAC ammunition following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear 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. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.




https://app.box.com/shared/static/2hex4netcnq7qqagacf8cy14hvdk36q8.jpg




The Wind Probe.

https://app.box.com/shared/static/lkg47ptc04.jpg




The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel. The barrel has a 223 Wylde chamber with a 1:8” twist. Prior to firing the 62 grain X-TAC ammunition, I fired a 10-shot control group using hand-loads topped with a 62 grain OTM bullet. That group had an extreme spread of 0.83”.




https://app.box.com/shared/static/xac10i5ekkey7ih9ej5a3n6nmv5gy4j9.jpg




https://app.box.com/shared/static/u06kxn74p5b37hm9yad51jdf802jb3jp.jpg




Next, three 10-shot groups of the 62 grain X-TAC load were fired in a row with the resulting extreme spreads:

2.76”
2.24”
3.07”

for a 10-shot group average extreme spread of 2.69”. The average horizontal standard deviation was 0.66” and the average vertical standard deviation was 0.76”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the 30-shot composite group was 0.88”.


The smallest 10-shot group . . .

https://app.box.com/shared/static/xhq71qou0ctix3qjr33kuv015a7dc768.jpg





The 30-shot composite group . . .

https://app.box.com/shared/static/8h4n87v78ae1vfzs3q550bpdtcjjrcj1.jpg




….

* There is also a 600 yard accuracy specification for M855, that is greater than the mathematical equivalent of the 200 yard specification.


....

[Molon]

A PRIMER ON THE MEAN RADIUS

The Mean radius is a method of measurement of the dispersion of shot-groups that takes into account every shot in the group. It provides a more useful analysis of the consistency of ammunition and firearms (accuracy/precision) than the commonly used method of extreme spread.

The typical method used to measure a group consists of measuring the distance between the centers of the two most outlying shots of a group. This would be the “extreme spread” of the group. We are essentially measuring the distance between the two worst shots of a group. Take a look at the two targets below.




https://www.box.com/shared/static/05kmhft6cvk0w96q771e.jpg




Most people would intuitively conclude that the second target shown is the “better” group. Measuring the two groups using the extreme spread method, we find that both groups measure 2.1”. Once again with the typical method of measuring groups we are measuring the distance between the two worst shots of the group. This method tells us nothing about the other eight shots in the group. So how can we quantitatively show that the second group is better than the first? (Yes, we could score the groups using “X-ring” count, but this does not give us any differential information about all those shots in the X-ring.) This is were the mean radius method comes in. It will give us that extra information we need to better analyze our groups, rifles and ammuntion. If I just reported the measurements of the two groups above using the extreme spread meathod, without a picture, you would assume that the two groups were very much the same. Using the mean radius method shows that the second group is much more consistent. It has a mean radius of 0.43” compared to 0.78” for the first group.

Mean radius as defined in Hatcher's Notebook “is the average distance of all the shots from the center of the group. It is usually about one third the group diameter (extreme spread)” for 10-shot groups.

To obtain the mean radius of a shot group, measure the heights of all shots above an arbitrarily chosen horizontal line. Average these measurements. The result is the height of the center of the group above the chosen line. Then in the same way get the horizontal distance of the center from some vertical line, such as for instance, the left edge of the target. These two measurements will locate the group center.

Now measure the distance of each shot from this center. The average of these measures is the mean radius.

Once you get the hang of measuring groups using the mean radius it becomes very simple to do. While being very simple to do, it is also very time consuming. Modern software programs such as RSI Shooting Lab make determining the mean radius a snap.

The picture below is a screen snapshot from RSI Shooting Lab. The red cross is the center of the group (a little high and right of the aiming point). The long red line shows the two shots forming the extreme spread or group size. The yellow line from the red cross to one of the shots is a radius. Measure all the radii and take the average to obtain the mean radius.




https://www.box.com/shared/static/e5h310mx2lw65cuuwrfk.jpg




Mean Radius Demonstration

Let’s say you fired a 5-shot group from 100 yards and the resulting target looks like this. (The X-ring measures 1.5” and the 10-ring measures 3.5”.)




https://www.box.com/shared/static/pn6jf1qeuywk5a42jzcz.jpg




The extreme spread of the group measures 2.83”, but we want to find the mean radius (or average group radius.) In order to find the mean radius we must first find the center of the group. By “eye-balling” the target most people would see that the group is centered to the left of the “X-ring” and probably a little high, but we need to find the exact location of the center of the group.

Locating the Center of the Group

The first step in finding the center of the group is to find the lowest shot of the group and draw a horizontal line through the center of that shot.




https://www.box.com/shared/static/hg77du60v6jwj6qnhsd2.jpg




Next, find the left-most shot of the group and draw a vertical line through the center of that shot.




https://www.box.com/shared/static/qyqecvzn8slmls96199f.jpg




Now measure the distance from the horizontal line to the other four shots of the group that are above that line. Add those numbers together and divide by the total number of shots in the group (5).




https://www.box.com/shared/static/k0uuxzzb1weo3ppgluz7.jpg




2.50” + 1.03” + 2.01” + 1.30” = 6.84”

Divide by 5 to get 1.37”. This number is the elevation component of the center of the group.

Next we need to find the windage component of the center of the group. From the vertical line, measure the distance to the other four shots of the group that are to the right of the line. Add those numbers together and again divide by the total number of shots in the group (5).




https://www.box.com/shared/static/ncg6hkbmcv1kyyvtdua1.jpg




1.76” + 2.54” + 0.45” + 1.19” = 5.94”

Divide by 5 to get 1.19” This is the windage component of the center of the group.

Finding the windage and elevation components of the center of the group is the most difficult part of this process. Once that is done the rest of the process is a piece of cake.

Using the windage and elevation components, locate the position on the target that is 1.37” (elevation component) above the horizontal line and 1.19” (windage component) to the right of the vertical line. This location is the center of the group!




https://www.box.com/shared/static/46cr6kei23k2npjbwopy.jpg




Determining the Mean Radius

Now that we have located the position of the center of the group, the first step in determining the mean radius is to measure the distance from the center of the group to the center of one of the shots. This line is a single “radius”.




https://www.box.com/shared/static/vm7k0jzt5h941pfldlhj.jpg




Now measure the distance from the center of the group to the center of each of the rest of the shots in the group. Add the measurements of all the radii together and then divide by the total number of shots in the group (5).




https://www.box.com/shared/static/lv461k9kjilx3jndshs4.jpg




0.85” + 1.35” + 1.38” + 0.84” + 1.61” = 6.03”

Divide by 5 to get 1.21”. This is the mean radius (or average group radius) of the group!

Using the mean radius measurement to scribe a circle around the center of the group gives you a graphic representation of the mean radius. This shows the average accuracy of all the shots in the group. This demonstrates why the mean radius is much more useful than the extreme spread in evaluating the accuracy of our rifles and ammunition.




https://www.box.com/shared/static/g1480t5ca47zrae1du8i.jpg




The table below will give you an idea of the relationship between the mean radius and extreme spread for 10-shot groups.




http://www.box.net/shared/static/e4ckmi2y36.jpg



....

[T2C]

Informative post as usual Molon. The Winchester Q3131A I fired out of my match rifle(s) would hold just under 6" at 200 yards. I don't believe I have ever fired Q3131A1. The Malaysian M193 was hot, but would hold under 4" at 200 yards.

My rifle(s) had a 1:7.75 twist. Groups were always shot in the prone position with a leather sling and no shooting jacket. A jacket helps a little during a match, mostly in the offhand position. Like you, I would not consider using a group for reference unless it was at least 10 rounds.

[bernieb90]

Molon,
Is there any explanation for the claim made in the article regarding M855, and M855A1 being more accurate in the 1/9 twist barrels?


I posted this one time on a forum and got some people claiming way tighter groups. It is PMC Bronze fired from a BCM ELW 16" barrel at 100yds.

35278

I got some people claiming much tighter groups in the 1"-1.5" range. I am not the best benchrest shooter, and it was a very light rifle with a stock Mil-Spec trigger, but it looks to be on par with what the ammunition is capable of. I am not sure if people are just selecting the tightest group and posting that or if there is something else going on.

[T2C]

Reloading ammunition for a High Power match is time intensive, so choosing readily available practice ammunition is a must. When Radway Green 62g was plentiful on the surplus market people in my area were winning club level reduced distance (200 yards) High Power matches with it. It shot very well out of 1:9 and 1:8 twist barrels, but not very well out of 1:7 twist 20" barrels. I haven't seen anyone do well with M855 or M855A1, but I can only draw from a sample of 40 to 50 shooters.

You make a good point about people cherry picking shot group sizes. Some will shoot 4 or 5 groups and pick the smallest group for reference. I am of the opinion that if you shoot three to four 1 MOA groups at 200 yards, then fire a 3 MOA group, you have 3 MOA ammunition.

That being said, a 1:7 barrel will shoot ammunition with a QUALITY 50g to 80g bullet very well.

[556BlackRifle]

Molon, my formerly 3 MOA Noveske Recce is starting to settle in. I now call it my 1.5 to 2.0 MOA rifle. This is a huge improvement over my previous outings with this rifle. :)

Best groups of the day. Just over 1 to 1.2 MOA with Federal XM193 Lot SMQ13M813S103. Clear, 73F, low humidity, no wind.

35289

[Molon]

I posted this one time on a forum and got some people claiming way tighter groups. It is PMC Bronze fired from a BCM ELW 16" barrel at 100yds.

https://app.box.com/shared/static/rhph1q8o2m03clh7xmf8pjd13eeonikb.jpg

I got some people claiming much tighter groups in the 1"-1.5" range. I am not the best benchrest shooter, and it was a very light rifle with a stock Mil-Spec trigger, but it looks to be on par with what the ammunition is capable of. I am not sure if people are just selecting the tightest group and posting that or if there is something else going on.




I evaluated the accuracy (technically, the precision) of the PMC Bronze 55 grain FMJ ammunition using my 20” stainless-steel Lothar-Walther barreled AR-15. This barrel has a 223 Wylde chamber with a 1:8” twist.

Three 10-shot groups fired in a row from the bench at a distance of 100 yards had the following extreme spreads:

2.22”
1.82”
2.15”

for a 10-shot average extreme spread of 2.06”. The 30-shot composite group had a mean radius of 0.72”.
The smallest 10-shot group . . .

https://app.box.com/shared/static/2af11wqqvyz7sxsl3tpoulg5hqyqs1ws.jpg



I'm willing to bet that not one of the Internet Commandos that claimed that they were getting "1 to 1.5 inch" groups with this ammunition from a distance of 100 yards, have posted verifiable pics of three 10-shot groups fired in a row from a distance of 100 yards using a semi-automatic AR-15 in order to support their claim.



....

[bernieb90]

This is what the guy posted for PMC Bronze out of a Nordic 18"

http://i82.photobucket.com/albums/j275/bernieb90/Group.jpg

[Molon]

This is what the guy posted for PMC Bronze out of a Nordic 18"

http://www.calguns.net/calgunforum/attachment.php?attachmentid=396400&d=1425853680

Pic isn't showing up.

[bernieb90]

I'm sorry about that it might have been the file location. Lets see if what I did fixed it.

[ClearedHot]

Is there any velocity differences between the 1:7 and 1:9 twist barrels of the same length?

[Molon]

This is what the guy posted for PMC Bronze out of a Nordic 18"

http://i82.photobucket.com/albums/j275/bernieb90/Group.jpg



I guess I should sell-off all my expensive Krieger barrels, unload all my expensive reloading equipment and components and just shoot PMC ammunition through a Nordic barrel. https://app.box.com/shared/static/s112hu8p8e.gif


...

[titsonritz]

This is what the guy posted for PMC Bronze out of a Nordic 18"

http://i82.photobucket.com/albums/j275/bernieb90/Group.jpg


My 10 shot groups look just like that...
35328





...@25 yards with an Aimpoint.