Hornady 5.56mm 55gr GMX

[jerrysimons]

Here is some 55gr GMX TAP 5.56 impacting at mid 2300's: https://www.youtube.com/watch?v=jmLFElw3QDQ
Here is some 55 GMX at barely over 2100fps: https://www.youtube.com/watch?v=sukRauELwFk
Here is Barnes 55gr TSX at 2150fps: https://www.youtube.com/watch?v=3Ht5Th0KtBk

Also, no, it is not the Superformance crap.

Stay tuned for Black Hills to release 70gr 5.56 pressure GMX sealed at the primer and case-neck. TAP GMX is only sealed at the primer from Hornady.

That Black Hills load will surely take the cake. Is SSA 556 70gr TSX sealed in either place?
Has anybody been able to figure out what the expansion threshold is for the 70gr GMX, earlier in the thread the numbers from hornady were first errors and then didn't seem right when 55gr GMX was lower than the 70gr.

[Jim D]

That Black Hills load will surely take the cake. Is SSA 556 70gr TSX sealed in either place?
Has anybody been able to figure out what the expansion threshold is for the 70gr GMX, earlier in the thread the numbers from hornady were first errors and then didn't seem right when 55gr GMX was lower than the 70gr.

I had zero issues with expansion when we shot the 70gr from my 10.5" barrel.

[WS6]

That Black Hills load will surely take the cake. Is SSA 556 70gr TSX sealed in either place?
Has anybody been able to figure out what the expansion threshold is for the 70gr GMX, earlier in the thread the numbers from hornady were first errors and then didn't seem right when 55gr GMX was lower than the 70gr.

No. SSA is not sealed or crimped primers.
The above poster got great expansion from an sbr. I believe full expansion at around 2400fps. Noone knows the floor.

[jerrysimons]

No. SSA is not sealed or crimped primers.
The above poster got great expansion from an sbr. I believe full expansion at around 2400fps. Noone knows the floor.

Roger. I like some of the benefits of the GMX, less copper fouling, soon to be available with fully sealed 556 loads, perhapse better performance through barriers but the 70gr TSX is known to expand down to 1800-1900fps which may still be a strength in comparison.

[vicious_cb]

Roger. I like some of the benefits of the GMX, less copper fouling, soon to be available with fully sealed 556 loads, perhapse better performance through barriers but the 70gr TSX is known to expand down to 1800-1900fps which may still be a strength in comparison.

Exactly, there is no free lunch. You want make a tougher bullet to get through glass intact and you are going to have to raise the min. expansion velocity. The 50gr TSX optimized has the highest expansion velocity out of all the TSX bullets. All the other TSXs can expand below 2000 fps.

[WS6]

Exactly, there is no free lunch. You want make a tougher bullet to get through glass intact and you are going to have to raise the min. expansion velocity. The 50gr TSX optimized has the highest expansion velocity out of all the TSX bullets. All the other TSXs can expand below 2000 fps.

Yet I've seen 55gr TSX's impact gel at well over 2000fps and just FMJ. Real-data is needed.

[BufordTJustice]

Yet I've seen 55gr TSX's impact gel at well over 2000fps and just FMJ. Real-data is needed.

Yeah, the 55gr TSX in the above video at 2150fps went FMJ.

Tis true it's a trade off.

[vicious_cb]

Yeah, the 55gr TSX in the above video at 2150fps went FMJ.

Tis true it's a trade off.

If hes using clear ballistics gel Im taking that with a huge grain of salt. Its a very poor medium for anything high velocity.

[Molon]

I also hope it doesn't suffer from the poor accuracy of the Super Performance 75 gr OTM noted in testing by Molon (I believe) over on ARF some time ago.

Hornady 75 grain 5.56mm Superformance: Update







In 2010, I posted a sneak preview of Hornady’s 75 gain 5.56mm Superformance ammunition. When chronographed from a 20” Colt M16A2 barrel, this Superformance load produced the highest muzzle velocity for a 75 grain load that I had ever seen; 2909 FPS. The table below shows the muzzle velocity of the Superformance load compared to other Hornady loads charged with standard powders.









Unfortunately, this increased velocity load came with a price; and I’m not referring to dollar signs. The accuracy of the 5.56mm 75 grain Superformance load was . . . how shall I say this? . . . sub-standard . . . for what myself and others here had come to expect from a “premium” heavy OTM factory load. The smallest 10-shot group that I obtained from a chrome-lined, NATO chambered, 20” Colt HBAR at a distance of 100 yards had an extreme spread of 3.4” and a mean radius of 1.16”. Others here who tested the load using match grade stainless steel barrels faired hardly better.














Since that time, Hornady has made a few changes to the 5.56mm 75 grain Superformance load. For starters (and of no real consequence) the boxes for this load now carry a “match ammunition” nomenclature instead of the original “Varmint” label. Secondly, this load is now seated with the 75 grain “T2” projectile instead of the T1 found in the original load.










Thirdly, the velocity of this 5.56mm Superformance load has been reduced. While the original load produced of muzzle velocity of 2909 FPS from a 20” barrel, the new version had a muzzle velocity of 2863 FPS for a difference of 46 FPS. Most importantly, this new version of the load has shown significantly improved accuracy over the original version.

Following my usual protocol for accuracy testing (which can be viewed in detail here here), I fired three 10-shot groups in a row from a distance of 100 yards from a Lothar Walther barreled semi-automatic AR-15 with the Hornady 75 grain 5.56mm Superformance “Mod 1” ammunition. The resulting 10-shot groups had extreme spreads of:

1.31”
1.93”
1.02”

for an average 10-shot group extreme spread of 1.42”. The mean radius for the 30-shot composite group was 0.48”. For comparison, three 10-shot groups fired from the same barrel using Hornady 5.56mm TAP T2 ammunition had an average extreme spread of 1.09” and 30-shot composite group mean radius of 0.34”.


The smallest 10-shot group of the “Mod 1” Superformance ammunition.






It should be noted that the Superformance powder creates a higher port-pressure for less than full-length gas systems compared to standard powders.








….

[Molon]

Hornady 5.56mm 55 grain GMX Superformance















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