Hornady 5.56mm 70 Grain GMX TAP Barrier


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Hornady’s 5.56mm 70 grain GMX TAP Barrier load uses the same 70 grain GMX projectile that is available as a reloading component.  The 70 grain GMX is a monolithic hollow-point, but unlike similar monolithic bullets such as the all-copper Barnes TSX, the Hornady GMX is made from gilding metal (95% copper and 5% zinc).  Hence the “GM” portion of GMX.
 


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The 70 grain GMX has a nominal length of approximately 1.048”, making it slightly longer than the 70 grain Barnes TSX.

 

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The Hornady 5.56mm 70 grain GMX TAP Barrier cartridge is loaded in Hornady 5.56mm brass that has crimped and sealed primers.  The 70 grain GMX bullet does not have a cannelure per se, but the top relief band of the projectile functions as one, with the case mouth crimped into this relief band.  The cartridge also has case mouth sealant that fills this top relief band.  The load is charged with “ball” powder.



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I chronographed the Hornady 5.56mm 70 grain GMX TAP Barrier ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel.


 
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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.

 

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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.

 

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Atmospheric conditions

Temperature:  73 degrees F
Humidity:  63%
Barometric pressure:  29.68 inches of Hg
Elevation:  950 feet above sea level


The muzzle velocity for the 10-shot string of the Hornady 70 grain GMX TAP Barrier  ammunition fired from the 20” Colt barrel was 2912 FPS with a standard deviation of 10 FPS and a coefficient of variation of 0.34%!

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 (and to give you an idea of how good the CV is for this factory loaded 70 grain GMX TAP Barrier ammunition) the mil-spec for M193 allows for a coefficient of variation of approximately 1.2%, 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%.

 

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I conducted an accuracy (technically, precision) evaluation of the Hornady 70 grain GMX TAP Barrier 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 used. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.



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The Wind Probe.

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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.



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Prior to firing the 70 grain GMX ammunition, I fired a 10-shot control group using a hand-load topped with the Hornady 50 grain V-MAX.  That group had an extreme spread of 0.75”.

 

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Next, three 10-shot groups of the Hornady 70 grain GMX TAP Barrier ammunition were fired in a row with the resulting extreme spreads:

1.34”
1.47”
1.16”

for a 10-shot group average extreme spread of 1.32”.  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 0.43”.
 

The smallest 10-shot group.

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The 30-shot composite group.

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Great work.  Thank you Molon!

As always, excellent work.

I didn't even know this round was out there.

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Range Dog is ready for the range . . .





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I've been getting around 1.5MOA from the Barnes loading, using my 16.1" DDM4 and an Aimpoint and later my Nightforce 1-4 FC-2 at 100 yards. Just 5 shot groups prone off the magazine, and seated off the magazine, though. This is some seriously accurate stuff!

Five-shot groups do not provide a true indication of the radial dispersion for a rifle/ammunition combination, unless you over-lay those 5-shot groups on each other from the aimpoint.

The Barnes 70 grain TSX itself is capable of decent accuracy. The 10-shot group pictured below was fired from one of my Krieger barreled AR-15s at a distance of 100 yards using a hand-load of the 70 grain TSX.  The group has an extreme spread of 1.12”




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The next examples pictured below are from factory loaded SSA 5.56mm 70 grain TSX ammunition fired from a 20” Noveske barrel with a 5.56mm Noveske Match Mod 0 chamber.  

I fired two, 5-shot groups in a row with the resulting extreme spreads of 1.22” and 1.91”.  I then fired a traditional 10-shot group, which had an extreme spread of 1.93” and a mean radius of 0.61”.

I over-layed the two 5-shot groups on each other using RSI Shooting Lab to form a 10-shot composite group. The 10-shot composite group had an extreme spread of 1.93” and a mean radius of 0.63”.




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Indeed.


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De rien.


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While I agree with you, sometimes I only bring a box or two of a certain round with me, and use 5 shot groups to zero. Most of my testing is actually me zeroing the weapon. Trends emerge over 2 to 3 five shot groups.

No, they don’t.  “2 to 3 five shot groups” are not statistically significant.  


In your own thread here, you claimed that Hornady 5.56mm 55 grain GMX TAP Barrier ammunition was “extremely accurate” and posted a pic of one 5-shot group from 100 yards that had an extreme spread of 1.35”.

I’ve conducted accuracy (technically precision) evaluations of two different lots of the Hornady 5.56mm 55 grain GXM TAP Barrier ammunition from two different AR-15 barrels at a distance of 100 yards using my bench-rest set-up.  The best combination of barrel and ammunition-lot produced three 10-shot groups fired in a row that had the following extreme spreads:

2.19”
1.47”
1.99”

for a 10-shot group average extreme spread of 1.88”.  Over-laying all three of the 10-shot groups on each other using RSI Shooting Lab produced a 30-shot composite group that had a mean radius of 0.62”.  This is hardly “extremely accurate” ammunition.  

In the graphic shown below, group #3 is the 30-shot composite group of the Hornady 5.56mm 55 grain GMX TAP Barrier ammunition.













1.  Prvi Partizan M193

2.  PMC 5.56 NATO 62 grain X-TAC

3.  Hornady 5.56mm 55 grain GMX TAP Barrier

4.  Hornady 5.56mm 75 grain  Superformance

5.  Black Hills 5.56mm 77 grain Tipped MatchKing

6.  Barnes Precision 5.56mm 85 grain OTM









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From George L. Jacobsen, Assistant Superintendent, Frankford Arsenal (Philadelphia, PA) . . .










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Five shot groups are inferior to 10-shot groups and for the same reasons that 3-shot groups are inferior. The differences between 5-shot groups and 10-shot groups aren't as dramatic as they are between 3-shot groups and 10-shot groups; but the differences are there, nonetheless.


Let’s take a closer look at the inadequacy of using 5-shot groups to evaluate the accuracy/precision of a rifle and ammunition. Utilizing thirty individual shots that I fired in a row on thirty different targets from my bench-rest set-up at a distance of 100 yards, I used RSI Shooting Lab to form six, 5-shot groups. The first 5-shot group was formed from shots 1-5, the second 5-shot group was formed from shots 6-10 and so on. The six, 5-shot groups are pictured below.









As you can see in the graphic above, the 5-shot groups suffer from the same deficiencies as 3-shot groups (albeit not to the same extent.) The 5-shot groups have significant variations in their extreme spreads from shot-group to shot-group. The largest 5-shot group (group number 5) is 2¼ times as large as the smallest 5-shot group (group number 6). The 5-shot groups still have significant differences in the locations of their group centers referenced from the point of aim.

(The Internet Commando’s cousin would have cherry-picked group number 6 to brag about the accuracy of his rifle and ammunition and pretended that the other five groups never existed.)





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Rick Jamison, the author of the Precision Reloading column in Shooting Times magazine approaches accuracy testing in a scientific manner.  He uses a machine rest for testing and fires 10-shot groups.  Here are his own words on the subject from one of his articles . . .

There are stories of a single bullet that for no explained reason flies out of what might have been a tight cluster. This often occurs with a three-shot string and many times with a five-shot string. If you're lucky enough to fire a group without a flier, you can end up with a very tight group. However, usually what happens if another five or seven shots are fired to complete a 10-shot string, other bullets fill in the space between the main group and the flier to make a reasonably rounded group. Ten shots are a more reliable indicator when it comes to predicting what a load is likely to do in the future.

The problem with 10-shot groups is that when you report them, everyone thinks you aren't shooting very well or that the ammunition is not good because the group sizes are so much larger than three- or five-shot groups. Also, when we're firing three- or five-shot groups with a flier, it is only natural to assume that it was caused by a flinch or "pulling" the shot. Therefore, since the flier was our own fault, the tendency is to eliminate it from any reporting of group size.

This is one of the advantages of using a machine rest... The machine rest reduces the human element.
After using this machine rest for several years, I have determined that a 1.5-inch 10-shot group at 100 yards... is a good one.





Rick Jamison's machine rest . . .






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Compared to Gold Dot, would you say that the Hornady is more, or less accurate? I only posted the best groups. However, when ALL of my 5 shot groups were taken into account, the Gold Dot 75gr showed to be roughly 0.5 to 1 MOA more accurate. Pretty similar to what you observed as a trend, no? I'm not saying 5 is as good as 10, or even statistically valid. I'm just saying that it pointed me the same direction.

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What is this 75gr SBR? I don't recognize that bullet

Hornady's newest load, designed for short barrel rifles.


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Rage report sneak preview.







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Molon,

I understand that Hornady 5.56 NATO 75 gr. SBR TAP ammo is designed for SBRs...  Would this bullet design be adequate as a man stopper, out of a 16" barrel, with acceptable accuracy?  I'm desirous of finding the best SD ammo I can find, that is as close to MK318 Mod 0, or M855A1, as possible...  Also in contention, Barnes 85gr ammo...  I've friends that have been many times to the Sandbox, and they relate stories of hitting a Hadji four and five times, without stopping him.  Thru and thru is not a good way to stop 'em...  Tomorrow I pick-up a 500rd case of 223 Rem - 64 Grain Hi-Shok SP - Federal Premium Law Enforcement, to go along with a half case of PMC X-Tac Rifle Ammunition 5.56mm 62 gr Green Tip, as well as another half case of Federal Fusion .223 Rem. 20 Rounds JSP 62 Grain F223FS1.  

Due to health challenges at 66, I've had to go from 7.62X51, down to 5.56X45.  I could no longer lift my rifles...  So, here I am...  However, my new rifle, an LWRCI DI is truly a joy...

Thank-You, Sir, for your time and kind consideration.  Likewise, many thanks for your experience and encyclopedic knowledge...  You've made my selections so much better...

GBY&Y's

CFL

Can we get this pic links fixed?

Bump for this request. Pics are the best part

I'll see what I can do.

Thanks for the efforts, Molon.

broken picture links repaired