That may not get you very far, as I understand the powder being used in the GMM is not sold as a canister powder (meaning you and I cannot buy the stuff), so you have little chance of replicating the exact burn rate and cartridge volume without fairly considerable experimentation.
As we speak I've been trying my best to duplicate the 175 GMM performance for my .308, I have a couple of good possibilities, but consistency seems to be lacking from loaded lot to loaded lot (it might be the high humidity in Houston, but I'm not really sure)
I agree with jeffvm, but in reality, all you need to do is replicate velocities (and accuracy) of the GMM. i.e. You already know the exact bullets (Sierra MatchKing 168 and 175gr) and you know the exact velocity at the muzzle (its printed in the federal ammo catalog at 2600fps) so you need a chronograph and lots of time to get the load that will launch the bullet at that velocity (of course, differing atmospheric conditions need to be considered) and then you are golden.
The powder they are using is RL15. They used to use a powder that closely resembled IMR4064. But they have sinced switched to the RL15 powder. Not sure what they are loaded to, I've never pulled one apart and weighed it. However there are much better loads out there than the Federal recipe, IMHO trying to duplicate it isn't the thing to do. By a little experimenting with both powders and seating depth you can work up a FAR superior load. Hope this helps
I don't what they are using if the GMM, but I've been devbeloping 600 and 1,000 yard loads for my Patriot Arms .308 using both Varget and Reloader-15 (for 155, 175, and 178 A-MAX grain bullets by Carteruccio, Sierra, Hornady, and Lapua). Almost without exception, the groups shot with the Reloader-15 are tighter and contain less vertical dispersion, notwithstanding some interesting velocity spread within each group.
In fact today's 5 shot groups from 100 yards averaged .300 and never exceeded .6 inches, and were spread from 45.1 grains to 46.3 grains in .3 grain increments. The problem with days like this is deciding where to zero in and fully develop a load. :lol: