Hornady Superformance GMX?

Melman

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I was wondering if some of you guys with knowledge of reloading could help me out with this question. looking at switching to some monolithic bullets for my .308 for Elk sized game and the nosler e-tip in particular is high on the list. In case my rifle doesn't shoot them well I was looking at the Hornady GMX option since I know my gun likes the 150 and 165g SST rounds. my question is, why does the GMX have a slower muzzle velocity than the same weight bullet in the SST? example .308 150g SST Superformance is 3000fps 150g GMX is 2940fps only 60 fps slower. but when you step up to the 165 grain GMX which I'd like to use for Elk its 90fps slower 2840 vs 2750. from what I can see they have the same ballistic coefficient and same weight. does it have to do with bullet length taking up power space? I've heard the GMX might not expand at lower .308 velocities very well. Does anyone have experience with this round on elk sized game?
 

sagebrush

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No experience with the GMX but I think you are correct in your assumption about the longer bullet being seated deeper.
 

Ben Lamb

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No experience with the GMX but I think you are correct in your assumption about the longer bullet being seated deeper.

And your seating off the lands is different w/ copper as well. I'm not a big fan of the Superformance line. Factory loads are notoriously over-pressure and show signs of it w/ flat primers, etc. I made the mistake of buying an 8 pound jug of the stuff and to date, only my 22-250 seems to like it.

If you are reloading, other less sensitive powders can give you the velocity you are looking for without the danger of being over-pressure.
 

brymoore

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I've had poor luck with GMX on elk and mule deer. Pencil threw hits with no blood for tracking.
 

Melman

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I've had poor luck with GMX on elk and mule deer. Pencil threw hits with no blood for tracking.
I've heard a lot of people say this. then some people say how much they like them.

thanks for the responses. Lets hope my rifle likes the 168g E-tip or I'll just stick with the good old 180 partitions for bigger game. I was just looking to go with a little lighter bullet to get a flatter shooting round.
 

Mthuntr

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You can't go wrong with either the E-tip or the Partition. I'm partial to Partitions although I shoot the 140gr E-tip in my 7mm-08 and have killed things dead with it (no recovered bullets). Don't overlook the Accubonds either.
 

belly-deep

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The lower velocities are probably the result of the bullet having more bearing length, which equates to more friction in the barrel. More friction produces higher pressures. The SST and GMX are probably loaded to the same pressure but the SST can sit atop a bit more powder.
 
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Copper is less dense that lead so to get the same bullet weight copper projectiles will always be longer eating up case capacity for powder at a certain point. As mentioned copper bullets tend to require a long jump to the rifling so that limits powder volume as well.
 

tarheel

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From the research I've done the solid bullets open up better at 2500 and above. The .308 won't be able to maintain that kind of speed much beyond 100 yds and then you're just poking holes through them unless you get a solid hit on bone. More recent testing indicates that they need to be about .150 off the lands for best accuracy and to keep pressures in line. I have a great article on that if I can find it.
 

HighDesertSage

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I've had poor luck with GMX on elk and mule deer. Pencil threw hits with no blood for tracking.

In 2013 my buddy had to shoot a bull 3 times at 70 yards with the GMX. The bullets where fragmenting on impact. I wouldn't use them. If you want a flatter shooting load look at the Barnes TTSX in 150 grain. I use a 150 .308 out of my 300 and I hold on fur out to 350. 400 is holding on the top of the backbone. This method has worked very well for me the last few years.
 
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Guess it all depends on how you define "full"

I'm sure the bullet engineers have a ratio of original diameter to expanded that is determined to be "full expansion" in quantitative terms. In the case of copper bullets they don't grow hugely in frontal diameter with additional velocity above the expansion speed but rather the pedals grow longer with minor gains in frontal diameter.

unleaded-bullets-05.jpg


Clearly more velocity and energy is a good thing and expansion is better until the point of the bullet breaking apart, but the frontal area clearly approaches a limit at some point.
 

belly-deep

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In 2013 my buddy had to shoot a bull 3 times at 70 yards with the GMX. The bullets where fragmenting on impact. I wouldn't use them. If you want a flatter shooting load look at the Barnes TTSX in 150 grain. I use a 150 .308 out of my 300 and I hold on fur out to 350. 400 is holding on the top of the backbone. This method has worked very well for me the last few years.

I think you must be confusing the GMX with the SST. The GMX has a solid rear shank, which would be a about impossible to fragment in a hunting rifle chambering. The petals may break off but the shank should continue to penetrate.
 

JLS

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I can't speak to the Hornady, but I've been using the Barnes TSX for many years and with very good results. If the Nosler E-tip won't shoot (which I doubt that will be a concern) then try the Barnes. They have a proven track record. I've used them in reduced 30-06 loads that were shooting about 2000 fps and they opened up on impact. Your .308 with 150 grain TSX bullets will be fine.
 

GAbearclaw

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Awesome article!

Here in the Socialist Republic of Kalifornistan I have to shoot non-lead in the areas I hunt. I have had amazing accuracy and expansion from the GMX in the Hornandy factory loads for my .270 (130gr GMX).

Accuracy compared to the Barnes non-lead factory ammo has been exceptional. Two buddies have the same rifle (Tika T3 stainless) and both had marginal groups with the Barnes. Seeing that I tried the GMX and have better groups at much longer ranges and have had awesome results on the 200lb wild pig and buck I have shot with them. I will say the same Barnes non-lead factory ammo shoots great from my .243, but the Tika and .270 much prefer the factory GMX.

Good luck, I wish I had room and time for another hobby, I used to love reloading to unwind after a long day. Seeing the home-built pile of quality ammo grow was always a welcome sight and made my happy...
 

nuevo_eph

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Regarding the GMX for a 30-06, I tried them out but could not get them to group as well as factory TTSX. And that picture below absolutely scares me since I would like to see at least the middle expansion (2700fps) out to 300 yards but it will already be under 2400 fps by then out of a 22" barrel. In fact, it drops below 2700 fps BEFORE 200 yards! Barnes supposedly opens up as well as GMX at about 200 fps slower, giving you that much more room to work with.

http://www.hornady.com/store/30-06-SPRINGFIELD-150-gr-GMX-superformance/

hornady_GMX_150.png


"Hornady .30/150 gr. GMX bullet expansion at various impact velocities.
Left to right: cut-away, unfired, 3400 fps, 2700 fps, 2000 fps.
Illustration courtesy of Hornady Manufacturing."
 

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