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: