The regulars on this site - smokeless powder muzzle loaders - sure do make things difficult and expensive. I won't go into my experiments using Unique in ordinary CVA and Rossi .50 caliber muzzleloaders, so as not to violate the rules here, but just one of my test results using 777 gives energies on a par with GM54-120's "200 gr at 2500fps", which is 2776 fp.
My test rifle in this instance was a Rossi .50, modified to use a 9mm primed cartridge in place of a 209 primer, 85 gr 777 (weighed), a 508gr .451swaged projectile and a 14.4 gr TC #170088252 Sabot. I got 1460 fps, which is 2421 fp of energy. The Rossi is max rated to use 3 Pyrodex 50 grain pellets and Barnes 250 or 300 grain copper projectiles, so hitting 3000 fp shouldn't be a problem.