308 GMM 168/175 gr clone load development

[Jimbeaux82]

Guys,

I recently launched on a load development program to clone the Federal Gold Metal Match loads in 168 gr and 175 gr varieties for my PA-10 (18" barrel) and my son's Aero Precision AR-10 build (20" barrel). Of course, I want to shoot 168 gr and he wants to shoot 175 gr, so double the work here. ha ha.

Anyway, I am using the following components: Nosler Custom Competition Blems in 168 and 175 gr, Federal Brass, CCI 34 7.62 Mil primers, COAL 2.800" to match the GMM lengths. The Federal brass was weight sorted with a max variation of 2 grains and I found them very consistent in weight, with 200 cases out of 300 falling into this weight range.

I tested 4 powders, being AA 2460, IMR 4064, Varget, IMR 4895. These seemed to be about the best powders referenced except RL-15, which I had not been able to find.

My son's rifle is a high quality build, and repeatedly shoots 175 gr GMM at 2615 fps and .8-.9" 5 shot groups. My PA-10 is a stock, low cost unit but shoots pretty well. PPU 168 gr match shoots 1" 3 shot groups and both 168 gr GMM and SSA shoot 2600 and 2660 fps and group around 1 1/4" for 3 shot groups.

It is interesting that my 18" stock barrel shoots a little faster than my son's 20" custom barrel. He clocks 2615 fps and I clock 2630 fps with 175 gr GMM. But his will consistently group considerably better.

So I am trying to replicate the accuracy and velocity of these blue ribbon loads with my handloads.

Here are the results of the testing. All groups for testing were 3 shots

175 gr loads, 2.800" OAL

AA2460 40 gr 175 gr NCC CCI 34 no readings
41 gr 2516 fps 3" grp



IMR 4064 42 gr 2505 fps 3" grp
43 gr 2566 fps 1 1/2" grp


Varget 42 gr 2513 fps 1 1/2" grp
43 grs 2577 fps 1" grp , 2 touching


IMR 4895 40 grs 2430 fps 3" grp
41 grs 2478 fps 1 1/2" grp

168 gr loads, 2.800" OAL

AA2460 41 gr 168 gr NCC CCI 34 2593 fps 1" grp
42 gr 2652 fps 1 3/4" grp


IMR 4064 41 gr CCI 34 2533 fps 1 3/4" grp
42 gr 2600 fps 1 1/2" grp


Varget 41 gr CCI 34 2539 fps 2" grp
42 grs 2594 fps 1 1/4" grp



IMR 4895 42 grs CCI 34 2625 fps 1 1/2" grp
43 grs 2684 fps too hot, primer leaking, only fired 1 shot


With the 175 gr loads in the Aero Percision 20" rifle, it definitely looks like it groups better as I push the velocity toward 2600 fps. I have eliminated IMR 4895 as I do not think I can safely reach 2600 fps with this combo. Varget and 4064 show promise , so I will increase to 43.3 grs 4064 and 43.5 grs Varget and re-shoot both with WLR primer and see what happens. Also, after running the test, I saw where magnum primers are recommended for the AA 2460 (ball) so will try a load of 41.6 grs with a WLRM.

With the 168 gr loads, i am going to reshoot AA 2460 with 42.0 grs and 42.5 grs using a WLRM. I will shoot 43.0 grs Varget and 42.5 grs 4064 using a standard WLR primer.

Hopefully I can increase the velocity slightly to where I want it and tighten up the groups.

The only other thing I was considering was re-shooting the best loads with a Federal GMM primer if I can find them.

Also, regarding reshooting the AA2460 with a mag primer, do you think that has potential to tighten up the groups? I know ball powders require mag primers particularly in cold weather but I have read where mag primers usually slightly open up the groups. Since I was shooting on a 90 deg day, and Louisiana temps seldom get below 30 deg, may not need the mag primers for reliable ignition. I would like your opinions on this.

Also, is there any other suggestions that you guys can offer in developing a GMM clone that I have not already tried? Other than what I have done and plan, I will start breaking down in .5 gr or less increments for the most promising loads.

Your suggestions and comments are welcome.

Jimbeaux

 

[Guy Miner]

I'll focus on the 168's - as I've seldom used the 175's - though they carry better at long range.

Years ago I was doing about the same thing - I was newly appointed to the SWAT team, in charge of our sniper section, and was issued 168 grain Federal Gold Medal ammo for duty and practice. Not much of it for practice. I found that it shot very well from my 24" Remington 700 rifle. Very well.

So - wanting to do more practice, I went about building a load that essentially duplicated the trajectory, accuracy & velocity of the factory match ammo.

Used the Federal brass - it proved to be a tad soft, but otherwise high quality - same as factory
Used the Federal 210 match primers - same as the factory loads
Used the Sierra 168 gr MatchKing bullet - same as the factory loads

Loaded to the same overall length as factory loads

Adjusted my charge of Varget to produce the same velocity as factory loads.

And what do you know? I got the same point of impact, and very similar accuracy. When I started using higher quality (Wilson) dies, I started getting better accuracy.

When I wore out the factory barrel (about 5,000 rounds as I recall) I had a Krieger put on, with the chamber cut for the 168 gr factory ammo. That helped accuracy too.

Found that I could substitute the Nosler bullet for the Sierra and suffer no problems. It was neither more or less accurate and the velocity remained the same.

So essentially I re-built the very good factory ammo with the same components & dimensions except for using Varget powder.

Worth noting that Sierra (at that point anyway) didn't recommend the heavier charges of Varget I ended up using. Hodgdon did, as did Nosler, so I cautiously worked my way up and got the velocity & accuracy I was seeking.

Getting about 2730 fps with the 168's, factory or my handloads, from the 24" barrel and it's produced groups as tight as 2.5" at 600 yards. I'm happy with that. The factory loads were at 2718 fps, my handloads at 2730 fps - figured that was close enough.

Regards, Guy

 

[Dwh7271]

As far as I am concerned, you just got the real deal from the "308 source". :grin: Can't improve on that.

What jumped out at me was this:

Adjusted my charge of Varget to produce the same velocity as factory loads.

That seemed to be what I was seeing from your list of loads, that none have yet duplicated the factory velocity. I'll bet if you get a load that hits that number it'll tighten right up.

 

[Jimbeaux82]

Guy,

that is precisely what I am trying to do. And from the initial tests it looks like Varget is the most promising. So I guess I will round up some Federal 210 M primers and slowly increase the charge of Varget until I get there.

Thanks

Jimbeaux

 

[Guy Miner]

Have also had good luck with CCI BR primers when Federal match primers were really tough to get.

Best of luck!

Guy

 

[Jimbeaux82]

Guy,

Please explain the Wilson dies set up for me as I am not familiar with it. I searched on Midway and found the Wilson seater dies but it said "for mallet or arbor press, not for conventional press". I am not familiar with an arbor or mallet press. The picture of the die does not show threads.

1) please explain your setup.
2) are you talking about the bullet seating dies only, or the resizing die as well? Some experts have the opinion that some resizing dies misalign the neck when the seater ball pulls thru it.
3) Redding and Foster make high quality micrometer seating dies that fit a conventional single stage press. Would they be just as good?
4) all of the loads I listed earlier were done using conventional RCBS 308 dies and seater. I have purchased a small base set but have not started using them yet.

Any other tips are appreciated.

Jimbeaux

 

[Jimbeaux82]

Guy,

did some research yesterday on google and youtube and understand the mallet and arbor press. decided to stay with a threaded die, so ordered Forster Ultra Seater dies in several calibers to try as well as a Forster Concentricity Gauge and will start paying attention to concentricity, something that I have not done before. Also saw a little tip of putting an O-ring below the lock ring on conventional resizing dies, similar to what is done on Lee dies, which theoretically allow the die and expander ball some latitude to self center, allowing the necks to be more concentric. Hopefully these steps, along with using match primers and refining the charge of Varget, will get me where I want to be.

Also working on developing a 5.56 mm 77 gr MK 262 Mod 1 clone. Almost where I want to be on that one as well.

Jimbeaux