I'm in total agreement with eldeguello.
150gr of 777 is WAY too much juice for all current muzzleloaders, with the Savage being the only possible exception.
Since 777 is 15 to 20% hotter than any other powder........that would would make a 150gr load of 777 the equivalent of 170 to 180gr of Blackpowder or Pyro <img src=icon_smile_shock.gif border=0 align=middle>.
Such a load is gonna stress the metal of the barrel and the threads of the breech.......not to mention all of the blow-back that's gonna be flying back in your face when the cap or primer is obliterated and blown in your direction.
Using magnum 777 loads has to be about the cloest thing there is to single barrel Russian Rulette.
"Every moving thing that liveth, I give unto you as meat" (Gen 9:3)
Trust God..........but keep your powder dry!