Federal GMM In Lake City brass

S

Stats Shooter

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A while back I posted a thread about trying to duplicate federal GMM ammo. And for the most part it was a successful endeavor. Here's the link to that thread.

But, alas, I have worn out the federal premium brass. After 8 loads the primer pockets are loose. So I needed to try and duplicate the load in different brass since federal premium is hard to find without buying factory ammo.

So I decided to try and duplicate the results in lake city since I have about 2500 or so pieces of lake city.308 brass. I decided to use Lake City 12 since that is the year I have the most of.

Case prep included annealing, sizing pushing back the shoulder 0.004", trim and camphor.

Primers CCI-BR2
Powder IMR 4064
Brass LC-12
Bullet 175 gr SMK
Seated to OAL of 2.800 or CBTO- 2.230 (SAAMI)

If you'll recall, Federal GMM uses Fed 210m, fed premium brass, 41 gr IMR 4064 and 175 smk's.

In my gun, with this lot of powder, it took me 41.3 gr 4064 to duplicate gmm velocities in federal once fired brass

In lake city brass it took 40.8 gr to achieve the same results. My groups at 200 yards with Federal GMM was around 1-1.5". With my gmm clone load I tweaked it down to a consistent 1" at 200 yards. With this load I was able to achieve about 1-1.5" groups at 200 yards.

Velocity in my 16.125" AR-10 is about 220fps below the 2600 fps federal GMM is supposed to achieve in a 24" barrel. With this load I had best results closer to 2400 fps than the 2380ish I got from the factory Federal

Hopefully the pockets in LC brass stay tight longer. This isn't a very hot load, but neither is GMM factory ammo. However, even at 2400 fps, these 175 gr smks stay above trans-sonic beyond 700 yards, which is more than enough out of an AR-10.
 
I use LC brass almost exclusively . It really can be hit and miss with it . It all loads well but some years seem to be better then others . I have a bunch of LC-14 and am not impressed with it . It seems to be softer then other years causing sticky bolts on loads other years or brands of brass do not .

To be clear this is with all other components being the same and velocities the same or lower as well as case volumes averaging with in a grain or less . So it appears the brass is just softer . I have to use a small base die for the first sizing ( first time since I started using LC brass ) which is now a least a couple thousand including multiple years . Right now I load LC 09 / 10 / 12 /14 . This also includes primer pockets already blown out from the original firing . 1 or 2% of the LC-14 cases I prime there is almost no resistance when seating .

That all said . when prepped right most LC brass loads very well for me . I have several loads that shoot consistent sub MOA with a few shooting 1/2 moa . Unlike you I've never been able to get my reloads to shoot as well as GMM . Or at least as good as my rifle shot it when new . My barrel has close to 4k rounds through it and has lost .075+ of it's throat . I shot some GMM about 700rds ago and it did not shoot well in my rifle any more . Best group at 100yds was 1.35 moa .
 
I'd generally shied away from mil brass, just didn't have much luck with it. Them I saw some LC Nat Match brass and tried it out. Stuff was super! Few weeks ago I needed some 243 brass and found some LC once fired range brass and decided to try it. All LC but a number of different date's. I didn't seperate them by date, just loaded them up. It is 308 stuff necked down to 243, I think it would work well for me anytime, I sure won't hedge at getting anymore! I've got a bunch of FA 49 30-06 brass but have never tried it with jacketed bullet's. Have only used it with cast bullet's and id did very well. I got the stuff ffrom a very good friend when he died and must have some 300 of them. Someday I'll out haow they do with jacketed bullet's.
 
Unlike you I've never been able to get my reloads to shoot as well as GMM
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As you have seen. There isn't any secret to GMM ammo. Have you tried a load workup with the same components?
And annealed the brass so that it is like new? I'm actually surprised that you can't do as well or better than GMM. Especially since you can easily get the exact same barrel time using a chronograph and Quickload.

One point though, I have not tried to duplicate the 168 gr GMM load. Mainly because the 175 shot about 1/3" better in my rifle so I went with that bullet/load.

In the 30 cal division of XTC matches my 175 GMM clone load is my go-to
 
Actually no I've never used all the same components . In fact not even close not the same bullet , case or primer . The first time I shot the rifle I used 168gr GMM and never used a 168gr bullet again . I load 175 , 178 and 190gr bullets . I've come pretty close to duplicating the accuracy with 178gr A-max , IMR 4064 , Rem cases and Win LR primers . Point of fact though is that I've never even bought 168gr SMK bullets to load which is what shot those truly incredible groups the first few times I shot the firearm .

I guess the moral to that story is I should stop saying I can't duplicate GMM because I've never actually tried it turns out . :rolleyes::(:)
 
I guess the moral to that story is I should stop saying I can't duplicate GMM because I've never actually tried it turns out .
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Uh, yea! The thing I really like about SMK's is, that their tried and true tangent ogive design makes them almost impervious to jump. For the shooter facing a magazine length restriction, this is excellent...and why I use them in my AR's (.556 and .308). I have also used them in a .300wm and in a .338 lapua and got the same boring 1/2 moa accuracy.

The one issue with them though, and it really isn't that big a deal, is that I have found there is no way to improve accuracy beyond adjusting powder. What i mean is, with Bergers, and other secant ogive bullets I have tried, you can adjust powder and seating depth to get to the "one bughole" accuracy assuming your rifle is capable. However, with SMK's, I have found that once you find the magic powder charge, adjusting seating depth won't make much difference. So if 3/4 MOA is the best at a given powder charge, it won't improve much by moving into or away from the lands...Again, this is a benefit when facing a mag length restriction, but could be a curse if you are loading single shot competition rounds. Also, the very same thing that makes the jump mostly irrelevant, makes the BC lower compared to secant ogive bullets.

But, you have to remember, Sierra's origional 168gr SMK was designed for 300 yard competition and was fortunate to find it also shot well out to 600 yards...The heavier bullets follow a similar design and it hasn't changed much in over 50 years.

But the point here is, I think you absolutely can duplicate Federal GMM accuracy and really the only components you need to stay the same are powder and bullet...The others like cartridge and primers will only adjust the amount of powder you need to achieve the same results. But the powder and bullet thing are kind of critical.
 
Awhile back I did a little science experiment which included Federal Gold Medal Brass and Lake City Brass (LC 13). There was some other brass included but I looked at case volume. I should have done neck thickness but omitted it. Anyway here are the results.

Case%20Volume.png


All the brass was sized and trimmed to uniform length. The average volume of LC 13 was 3.541cc and the Federal GM Match stuff was 3.550 which is not a heck of a lot of difference. I am not sure how much LC brass varies year to year or lot to lot? I have been loading quite a bit LC 13 and WCC 10 as I got a pretty good deal on several thousand of them. :)

Ron
 
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