anyone using the 120gmx?

[rasp65]

Sneaky 1
According to the Hornady web site "Compatible with conventional reloading data ". is one of the descriptors for the GMX.

[JASmith]

Ja smith, your quick load is hopefully up to speed on the gmx, it's a long bearing surface bugger!...

I hear you!

I've had a little trouble with the 120TTSXBT in QL -- but got some suggestions on how and what to tweak. Should be interesting to see how the GMX works against real data in the Grendel!

[sneaky one]

Good luck JA, hope you can find decent speed.,, I'm going for 2700 fps to help expand the 95's more than the 100's I made. I was handed a few 140 hot-cors to try,, even that unit is shorter than the gmx. Have fun. Let us know, pm me if you have a Ques. or 2.

[sneaky one]

Rasp. I saw that on the hornady site too, but 2300- 2350 like the 129 sst speed is pretty low for good expansion on this new unit. To reiterate, I maxed out for a safe load with my 100grn. over 28.8 x-term with a speed of 2550,, with decent expansion. I want a bit more tho.. I'm tryin to get these photos up on here, yet something's not connecting.

[LRRPF52]

here it is 1.403"
I have some loaded right now waiting to shoot for test loads, I loaded them to 2.25 or 26 cant remember right now.

Is this the 120 GMX in the picture? I saw earlier on here that it mic'd at 1.300", so I'm a little confused now. Is that a solid bullet? Looks like it would great in a 6.5x47 or .260 Rem at that length. I bet I could push that at over 2900fps in my AR10. The tips would probably provide more consistent BC's from projectile to projectile, and maybe help resist barrel extension/feed ramp damage to the ogive.

LRRPF52

[toolsofthetrade]

Is this the 120 GMX in the picture? I saw earlier on here that it mic'd at 1.300", so I'm a little confused now. Is that a solid bullet? Looks like it would great in a 6.5x47 or .260 Rem at that length. I bet I could push that at over 2900fps in my AR10. The tips would probably provide more consistent BC's from projectile to projectile, and maybe help resist barrel extension/feed ramp damage to the ogive.

LRRPF52

Yes that is the 120gmx, it is basically almost the same as a barnes, except the material it is made out of, IIRC.

[LRRPF52]

Gents,

I just looked up the posted BC for the 120 GMX on Hornady's site, and they list it at .480, which has to be a G1 value. The Barnes 120 TSX BT has a posted BC of .381, which makes the GMX a different cat in my book. I wonder how well it bucks the wind at 2890fps and faster? Gonna have to try some in the .260 I think. That could end up being a great mountain rifle bullet out to 500 yds on game if it doesn't deflect too much. That is a very long bullet for its weight...more like a 142 SMK or a 140 Berger.

LRRPF52

[JASmith]

Adding BC info to those posted by LRRPF52, I get:

• 120 GMX -- .480
• 120 TSX BT -- 0.381
• 120 TTSX -- 0.443 (from the JBM Web Site)
• 100 TTSX -- 0.359 (from the Barnes Catalog)

That little chunk of plastic in the TTSX seems to make a big difference! It also looks like Hornady did a lot of work to shape the GMX.

Does anyone have plans to chronograph the 120 in close and at range so we can back out a BC?

BTW longdayjake seems to have had good results with the 100 grain TTSX:

http://www.65grendel.com/forum/showthread.php?54-100-grain-TTSX-load-success

[toolsofthetrade]

I just got my upper back today and should be shooting my test loads this weekend at the latest. I will post the results

[toolsofthetrade]

OK, update...don't bother....at 100yds they were not stabilizing, not BAD, like keyholeing, but definitely not impacting straight.
here is a pic of the entire target, the two groups that are decent are factory 123gr Amax Hornady ammo for a base, the 120gr GMXs are the other scattered holes, shotgun pattern to say the best. this target is at 100yds there were three loads tried with 4 rounds each. all of them were like this.

Here is a close up of the 120 gmx's

here is a measure of the 123 gr hornady factory ammo group, basically 1st group I fired out of this gun.

and here is the 1st group I shot with the 95gr Hornady Vmaxes, this is my starting load of 28.5gr of 8208, this is 4 shots, I then got called away from the range on family drama crap.

[toolsofthetrade]

here is the rifle BTW

[JASmith]

Your twist may be a tad slow for the long bullet. How many inches per turn? (1-10"? 1-8"?)

Per JBM, the stability factor should be at least 1.5. The bullet is dynamically unstable when the factor is less than 1.0 and the bullet will tumble.

Here's what JBM gives for stability factor at the muzzle for the 120 GMX at 2550 ft/sec:

1-10" twist: 0.859
1-9" twist: 1.050
1-8" twist: 1.329
1-7" twist: 1.736

These are for the 1.403" length.

Bottom line, if your rifle has a 1-9" twist, the bullets are marginally stable, meaning that you'll likely see results like what you show.

[toolsofthetrade]

yup, that's what I got 1-9

[sneaky one]

Finally some photos of GMX 's

Here is a start to my Grendel photos. On the left is a 6.5 / 129sst. next is a stock 120 GMX. Next is a 100 gmx. Lastly the 100 gmx I recovered from my first deer in 2010

[sneaky one]

best photo I have of the best group from the 100 gmx. more to follow.

Awesome bullet, just too long at 120 grns.