Hornady .308 GMX 165 Gr Load problems, IMR 4064

[teeteemongo]

Hey guys could use some help here and I'm sure others are in my boat as well.

I'm looking at the 7th edition of the Hornady reloading manual and it has no information on the GMX lead free bullets that a lot of us have to use down here in SoCal. Powder I'm using is IMR 4064, which incidentally is missing from the 165 listings.

I've read online that people recommend to use SST load data as it should be interchangeable. Just to be on the same side though (as the 165 gf GMX bullets are WAY longer than even the 180gr SST), I called up Hornady and they recommended to follow 165 SST Varget loads except that GMX MAX loads will be two grains less in comparison to its lead core SST counterpart) COL they said was 2.750.

Varget for 165gr SST is 44 gr Max (42 should be max). I used 40gr for my GMX load to start with but would like to eventually move up to 42. My problem is that even at 40 grains, I'm hearing the powder crunching, obviously a compressed load already.

Anyone else know if this is normal for a load 2 grains below max?

Thanks guys, and I'll post up Hornady's response to the compressed load inquiry when Monday comes around.

[mecam]

I load a 175gr .308 Nosler HPBT with IMR 4064 at 43.5gr (compressed) and no signs of over pressure. Have shot over 100rds and no problems and 1/2" moa accurate.

You can use this as a guide
165 GR. HDY SP IMR IMR 4064 .308" 2.750" 42.0 2554 47,700 PSI 46.3C 2767 59,700 PSI

visit http://data.hodgdon.com/cartridge_load.asp



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[teeteemongo]

Thanks mecam, yeah i've looked at that specific load entry with IMR but have also read from somewhere that GMX gilding metal bullets have a longer contact surface and loads have to be adjusted accordingly due to the higher friction. Again, I could be totally wrong though, cant seem to remember where I read this... I've never fired compressed loads below max data so this is a first for me!

[mecam]

Thanks mecam, yeah i've looked at that specific load entry with IMR but have also read from somewhere that GMX gilding metal bullets have a longer contact surface and loads have to be adjusted accordingly due to the higher friction. Again, I could be totally wrong though, cant seem to remember where I read this... I've never fired compressed loads below max data so this is a first for me!

How long is your bullet and I'll measure my 175gr for comparison to get an idea. Probably, the best thing is start low and chrono your way up. Just watch for pressure signs.

[gottarollwithit]

Are you running a 2.8" OAL?

You're on the right track. Just slowly work it up. If it's just a little crunch, don't sweat it. When i called Hornady they said something about these bullets not conforming to the barrel as much as lead, but i don't remember much after that. You might benefit from using a slightly denser powder, which will allow you to fit maybe another grain or two in to your case. Varget might help.

And.... to be perfectly honest with ya, i think these bullets are more intended for use in 30-06 b/c to really get them to expand well you have to push them past 3000 fps. The Hornady rep did claim that they expand at slower speeds than that, but how much slower i couldn't get him to specify. That's not to say i'm not going to use it in 308 though... Twill just have to push it harder!

Here's one of my old theads:

http://www.calguns.net/calgunforum/showthread.php?t=298255

[ar15barrels]

Varget for 165gr SST is 44 gr Max (42 should be max). I used 40gr for my GMX load to start with but would like to eventually move up to 42. My problem is that even at 40 grains, I'm hearing the powder crunching, obviously a compressed load already.

Anyone else know if this is normal for a load 2 grains below max?

Thanks guys, and I'll post up Hornady's response to the compressed load inquiry when Monday comes around.

Here is a Quickload simulation.
This is NOT tested reloading data.
It's simply a computer simulation.
Work up your own loads accordingly...

Cartridge          : .308 Win.
Bullet             : .308, 165, Hornady GMX 30470
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 24.0 inch or 609.6 mm
Powder             : IMR 4064

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.595% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-06.0   99    39.50   2513    2314   45942   6504     96.1    1.280
-05.4  100    39.75   2528    2342   46798   6542     96.3    1.269
-04.8  100    40.00   2543    2370   47683   6580     96.5    1.259
-04.2  101    40.25   2558    2398   48578   6616     96.7    1.249
-03.6  102    40.50   2573    2426   49491   6652     96.9    1.239
-03.0  102    40.75   2588    2454   50423   6687     97.1    1.229
-02.4  103    41.00   2603    2483   51372   6722     97.3    1.219  ! Near Maximum !
-01.8  103    41.25   2618    2512   52340   6756     97.5    1.209  ! Near Maximum !
-01.2  104    41.50   2633    2540   53328   6789     97.6    1.199  ! Near Maximum !
-00.6  105    41.75   2648    2569   54335   6821     97.8    1.189  ! Near Maximum !
+00.0  105    42.00   2663    2598   55362   6853     98.0    1.180  ! Near Maximum !
+00.6  106    42.25   2678    2627   56410   6883     98.1    1.170  ! Near Maximum !
+01.2  107    42.50   2693    2657   57479   6913     98.3    1.161  ! Near Maximum !
+01.8  107    42.75   2708    2686   58570   6943     98.4    1.152  ! Near Maximum !
+02.4  108    43.00   2722    2716   59683   6971     98.5    1.143  !DANGEROUS LOAD-DO NOT USE!
+03.0  109    43.25   2737    2745   60819   6999     98.7    1.133  !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba    105    42.00   2701    2673   58379   6842     98.9    1.154  ! Near Maximum !
Data for burning rate decreased by 3% relative to nominal value:
-Ba    105    42.00   2622    2518   52379   6835     96.7    1.207  ! Near Maximum !

[Fjold]

IMR4064 is a coarse grained extruded powder so it is very bulky. I use it for 165 grain loads in a 308 at 43-44 grains. It is a compressed load so I swirl the powder as it goes down the powder funnel. You can also use a long (12" or so) drop tube to align the powder kernels so they pack better.

I use IMR4064 in my 375 H&H with the Barnes 300 grain TSX bullet and have to compress them a lot to get them to seat.

[teeteemongo]

Mecam, I measured the 165 GMX bullets, and they come out to 1.425". Its a little bit longer than even the 180 SST bullets. I should note that Hornady recommended a COL of 2.75, mine measured in at 2.76.

Thanks to ar15 for the simulation. It makes me a little worried knowing that I'm approaching near max loads like I suspected as well as the fact that you ran the sim with a COL of 2.80, I wonder if my specs are still safe.

Eh... I'm heading to Angeles today with my day off and will report back how the above load works.

Thanks guys for the follow ups, it's just ashame that these GMX bullets need a high velocity to perform yet a lot of powders for 308 wont be able to push it close to 3000 without too much pressure. Hornady needs to come out with something concrete on these bullets too!

[mecam]

Mecam, I measured the 165 GMX bullets, and they come out to 1.425".

Yep, that is long. My Nosler 175gr only measures 1.250"