Hornady 70gr Gmx - real world bc?

[StainlessSlide]

I'm sold on the new Black Hills 70gr Gmx load. I haven't yet had a chance to shoot it at long range. Does anyone have a estimate of the real world bc for this bullet, at ranges of 400-500m?

Hornady gives a G1 of .350, but this seems a little high to me due to the meplat size.

[WS6]

I do not find it optimistic. More to a BC than just Meplat, by far. I do not have proof one way or another, but check out the Gold Dots from Speer. The 75gr is 0.373, and the 62gr is 0.31, although that is above 3,000fps, I think, and below 3K it's 0.27, still, the 70gr GMX is a LOT slicker than the 62gr Gold Dot at every point, IMO

[StainlessSlide]

In the last few days I have been shooting the Black Hills load of this bullet at ranges from 100yd to 800yd, and measuring drop . My velocities were 2742 From 14.5" and and 2935 from a 20", on an Oehler 35. I input temp, humidity and altitude into a ballistic solver, and my best estimate of G7 bc is the very low .139

My only explanation for this is the meplat, the drag from the driving bands, and the long length of the bullet. The long length is caused by the low density gilding metal alloy. A long bullet gives what drag modelers call a large "wetted area", which means a large area in contact with the viscous atmosphere.

Using similar field techniques, I have estimated the G7 bc of the 62gr TSX at .130. This is consistent with Litz's measurement of the G7 bc of the 62gr TTSX.

[Kansaswoodguy]

I read an article once that estimated Hornady's numbers at about 3-5% high on the bullets they tested. I'd post a link if I had any idea where I read that. I think it was a something for the military if I remember correctly. Don't take this to mean I'm a Hornady hater I shoot a ton of their bullets and love them.

[vicious_cb]

External ballistics aside the report I've been seeing show that the GMX bullets have worse terminal ballistics than their TSX counterparts like shedding petals and having smaller expanded diameters. I'd would probaby move back to the 70gr TSX at this point.

[WS6]

External ballistics aside the report I've been seeing show that the GMX bullets have worse terminal ballistics than their TSX counterparts like shedding petals and having smaller expanded diameters. I'd would probaby move back to the 70gr TSX at this point.

My curiosity is...what happens at longer distances? The 55gr GMX does VERY well at expanding and holding together, in my experience. I think I should like to see some of this 70gr stuff at 100+ yards. It may very well go all MK318 SOST at <100 yards, but beyond? I dunno. It is very accurate and has a decent BC.

[vicious_cb]

My curiosity is...what happens at longer distances? The 55gr GMX does VERY well at expanding and holding together, in my experience. I think I should like to see some of this 70gr stuff at 100+ yards. It may very well go all MK318 SOST at <100 yards, but beyond? I dunno. It is very accurate and has a decent BC.

From what Ive heard the 55gr GMX preforms well and doesnt have the issues the 70gr GMX is having. My concern with 70gr GMX long range performance is that it has a higher expansion threshold of 2000-2200 fps AND a lower expanded diameter vs the 70gr TSX which has been proven to expand down to 1900fps.

[WS6]

Well, I tested both at 100 yards in water filled milk jugs. The 70 fragged the petals and tumbled. The 55 performed flawlessly. The 70 stopped in the 3rd jug, the 55 penetrated 4 full jugs, but was contained within the 4th, thiugh the 4th was leaking from both sides. Didn't quite punch through. Pix when I get home.

The 55gr measured .45" at the widest, and .43" at the narrowest. I did not bother with the 70gr GMX, as I view it as a non-viable failure for hunting.

40930

For whatever reason, the 55gr GMX penetrates like crazy in both my testing, and other tests. My testing shows that it will punch as much or more water-filled milk-jugs as 62gr TSX, and more than 64gr RA556B or 62gr TBBC. Independent testing by ATK (a competitor) shows it penetrates a hair over 20", and expands to 0.438 in 4LD / Gel. Ironically, this is IDENTICAL, statistically, to the expansion I am showing in my tests. Hornady claims 17" and 0.5" in bare gel. All sources I have found show this to be a VERY hot round, leaving a 14.5" barrel at nearly 3100fps, and a 20" barrel at almost 3300fps. Accuracy in my testing, as well as that of others, shows 1.5-2MOA accuracy, and I have noted POI is similar to M193, enough so that training out to 300m should not be compromised leaving your zero set for the GMX load.

Reduced velocity testing from a 7.5" AR pistol shows robust expansion, as well.


https://www.youtube.com/watch?v=jmLFElw3QDQ