GMX Load Data?

[Papajoe222]

I'm fairly new to reloading, so please bare with me.
I'm having trouble finding any info on the Hornady GMX bullets. What I have been able to find are references to using the SST data for load work-up. There doesn't appear to be any, easily available info on OAL. Everything I've been able to find refers to monolithic bullets in general and the consensus is to start well off the lands (.050). With this bullet, I end up with a compressed load @ 1.5gr over the recommended staring charge.
If I'm avoiding excessive pressure by seating well off the lands, am I not defeating that with a compressed load? If anyone has experience with these, any insight would be appreciated.

 

[DPI7800]

Well it may help if you list the caliber, bullet weight and powder and then you might get more information.

 

[jmr40]

Copper bullets in the same weight are longer than lead so they take up more space in the case. For a variety of reasons it is advisable to drop down 1 or 2 bullets lighter than you'd normally use with lead.

Because of more bearing surface on barrels and other factors you'll need a lower powder charge to reach max loads with copper compared to conventional bullets.

You could use standard load data, start low and work up carefully. Using a chronograph you'd know when you are approaching a max load. I wouldn't do this without a chronograph.

You might also look at load data for Barnes bullets. It should be VERY close, especially compared to conventional bullet data. There is a lot more info out there for Barnes bullets. Including their website.

http://www.barnesbullets.com/load-data/

 

[T. O'Heir]

You do not require bullet specific data.
Forget the off-the-lands stuff until you have worked up a load. It's just a load tweaking technique that isn't necessary.
"...a compressed load..." Has nothing to do with the OAL. They're nothing to worry about either. Compressed loads just reflect the relative size of the powder kernels and that's all.
Like jm40 says, a solid copper bullet is a solid copper bullet. Load by the weight using solid copper bullet data.

 

[Unclenick]

Uhhh. No. Mr. O'Heir is thinking of tuning bullet jump for accuracy. That is different from just making sure there is some jump to keep the pressure down. You will probably find that 0.030" jump will do that well enough, but 0.050 is fine.

The consequences of compression aren't a gimmie. You can get pressure rise that way with some powders—Trail Boss data warns against it, for example—but it can also reduce effective powder burn rate by jamming the grains closer together so the flame front propagates more slowly through the powder mass. So you can't know which way it's going until you experiment. This is part of why we start with the bottom load and work up.

This plot is for a round nose bullet and the amount of distance from the throat is less to get the same effect with a pointed bullet, but this gives you an idea of the general principle at work. You can see there is a pressure minimum point after which seating deeper raises pressure again due to using up too much powder space. Where this will happen for you is unknowable without experimentation. Since we have no idea what chambering you have, it is impossible to guess. In general, though, the larger the ratio of case volume to bullet diameter, the less effect each additional hundredth of an inch of seating depth has toward raising pressure.

If you are using a stick powder, you can pre-compact the powder considerably by using a long drop tube to dispense it into the case. Just be sure the powder you dispense to work the load up is done the same way to try to even the burn rate out.

In QuickLOAD, in a .308 Winchester, using the pressure and ballistics for a 165 grain cup and core bullet with IMR 4064 powder and then substituting the 165 grain GMX, the load required not quite 5% less powder, so that's a place to start. Final velocity was lower, but peak pressure was pretty close to the same.

Don't get caught up in friction surface area and the like. Hornady puts a couple of grooves in the GMX to help reduce the difference. It's still a harder object than a cup and core bullet though.

When it comes to COL and load data, you can do worse than consult the bullet maker. Call Hornady or email them. They will tell you the nominal COL over the phone and will usually send you some load data for the bullet if they have it for your chambering.

 

[disseminator]

I'm fairly new to reloading, so please bare with me.
I'm having trouble finding any info on the Hornady GMX bullets. What I have been able to find are references to using the SST data for load work-up. There doesn't appear to be any, easily available info on OAL. Everything I've been able to find refers to monolithic bullets in general and the consensus is to start well off the lands (.050). With this bullet, I end up with a compressed load @ 1.5gr over the recommended staring charge.
If I'm avoiding excessive pressure by seating well off the lands, am I not defeating that with a compressed load? If anyone has experience with these, any insight would be appreciated.

Hi,

Hornady doesn't publish their data online because they want you to buy their reloading manual. In the Hornady 10 manual, Hornady lists the GMX right along with the other bullets they make in the various calibers and weights.

If you are new to reloading, and you like the Hornady bullets, why not pick up a copy of the Hornady 10 reloading manual? It will tell you all you want to know about the GMX and other Hornady bullets.

 

[old roper]

Hornady new manual # 10 has same loading /seating depth all bullet same weight.

Nothing in manual about special seating depth for them. I've never shot GMX but I had Nosler E-Tip and Barnes.

 

[Unclenick]

Hornady doesn't publish their data online because they want you to buy their reloading manual.

But if you call Hornady support to ask about a specific bullet for a specific cartridge, they will usually email you the data for that one round and bullet weight. 1-800-338-3220

Hornady new manual # 10 has same loading /seating depth all bullet same weight.

Look again. Almost every bullet has its own COL next to its picture. Page 164 has separate loads and COL for the 50 grain GMX (2.165" COL). Page 167 has separate loads and COL for the 55 grain GMX (2.185" COL). Page 171 has separate loads and COL for the 70 grain GMX (2.235" COL).

The OP has not told us which one he is using.

 

[RC20]

The bullet mfg do not list different loads for the Coppers.

Ergo, any bullet data from them can be used if you start low in their charge range.

With the 150 to 155 Hornady in X, 10 bullets are listed all with the same starting and same ending loads.


Accurate Charts shows a 150 SP (Hornady by coincidence ) with a start load of 41.4 with a max of 46

Hornady X shows the same at 36.8. Max is 43.3
Start at the bottom with any listed charge

Go with the low of any source and I suspect (opinion) you would be fine.

 

[RC20]

If you are new to reloading, and you like the Hornady bullets, why not pick up a copy of the Hornady 10 reloading manual? It will tell you all you want to know about the GMX and other Hornady bullets.

As much as I like Hornady it really does not tell you anything about their specific bullets.

The COAL is generic to some and not others but 5 are the same COAL, two more are within .005.

They are more baize to lower loads than a quick scan of the powder mfgs.

 

[Unclenick]

The bullet mfg do not list different loads for the Coppers.

Please go back up before your own posts and read my second response in post 11. Pick up your copy of Hornady #10 and confirm what I said. The loads for the Hornady GMX bullet ARE DIFFERENT from their loads for their other same-weight bullets. Not much different for some powders and bullet weights, but over a grain different at maximum for others.

Examples for .223 Rem from pages 163 and 164 of Hornady #10:

50 grain lead core bullet maximum loads:
Benchmark: 25.8 gr
748: 28.3 gr
IMR 8208 XBR: 26.5 gr.

50 grain GMX maximums:
Benchmark: 24.6 gr
748: 26.1 gr
IMR 8208 XBR: 25.3 gr.

Some powders are outliers, like TAC with the 50 grain weight, but we all know the limits of precision of the process at the time of the testing , the powder lots, etc., can make that happen. The point is the trend is for the solids to have lower loads.

For a bigger difference in principle, look at Hodgdon's data where they have a lead core and a solids of the same weight and you will get two different tables of load data. The 55 grain Speer soft point and 55 grain Barnes TSX FB in .223 for example. The starting load Varget for the former is 25.5 grains, and the maximum load for the latter is just 24 grains.

M.L. McPherson shot every 130 grain .277 bullet he could get through a .270 Win pressure gun and got over 30% difference in peak pressure using the same load with all. Nearly twice what worst case SAAMI MEV (Maximum Extreme Variation) would allow for cartridges within a lot.

 

[old roper]

I didn't look at 22 cal bullets,my mistake but the 130gr GMX for the 270 is listed same loading data for all 130gr that Hornady makes and same COAL. 7mm 139gr GMX same loading data for all 139gr Bullets Hornady makes. You pick only 2 bullets and they only list it with 223 and 22-250 they list 50gr GMX but not 55gr GMX. It seems pretty selective in 22 cal, again I didn't look and if I did I would mention why they didn't test those bullets in 220 Swift and other 22 cal rifles.

 

[Unclenick]

Some of that is just how the data is organized. If you look at pressure-based data, like Hodgdon's, you find there are maximum charge differences between the bullet types. Hornady's manual is velocity based, usually in 100 fps steps for rifle. So, if I have a listing of theirs for 2700 fps, the individual bullets in the list might actually go anywhere from 2650 to 2749 fps with that charge weight, but still round into the same column. When the column it their maximum velocity, then you can expect one of the bullets approached their trusted pressure limit, but the others were likely lower in average peak pressure. As long as the difference across the span doesn't go over into the next column, then they don't report different load data for the bullet. But if you get a Pressure Trace and a chronograph and all of the bullets on the page for yourself and shoot them all with the same load, you'll be able to identify differences.

In the .223, the difference in seating depth for the longer solids eats up a bigger percent of the powder space, so I think they just didn't find enough matching or close-to-matching loads to keep the bullets in the same data table, even though some powders, like TAC, would have let them do so.

Because the solids are longer for weight than lead core bullets, they need faster twist for good stabilization than the same-weight lead core counterparts do. This is why the heavier ones, like the 70 grain, show up for use in a 5.56 NATO chamber with 7" twist barrel, but you won't find it listed for .223, for which they use the common 12" twist. In the .222 Remington, with 14" twist, you don't see even the 50 grain GMX listed. Too long to stabilize well in that slow twist barrel.

 

[RC20]

Please go back up before your own posts and read my second response in post 11. Pick up your copy of Hornady #10 and confirm what I said. The loads for the Hornady GMX bullet ARE DIFFERENT from their loads for their other same-weight bullets. Not much different for some powders and bullet weights, but over a grain different at maximum for others.

I will do so when I get home, I was using data from the 30 caliber group, and did list the grain of bullet so obvious it was in the (270 and larger?) groups, I didn't say it and should have.

I never figured there was a solid in 223, so much for JTC.