I agree with everything Triple Seven and Mark Whiz say with one exception. I have a stainless .50 Omega and any combination of 777 powder loose or pellets cause a crud ring in my rifle that is more trouble than I care to deal with. Even with my .25ACP conversion to use rifle primers the crud ring is still about 20% there. If you cannot find Black Mag3 (which is now my powder of choice for my Omega) I would try to find some American Pioneer Powder and I agree use fffg only not the ffg (too coarse). Next choice would be Pyrodex loose or pellets. I would try a 50gr. and a 30gr. pellet if you can get both sizes to give you an 80gr. charge. My rifle shoots that charge under a 295gr. or a 348gr. Powerbelt just fine. I shoot 300gr. Hornady bullets but switch the sabot to Harvester brand as the Hornady sabots are too thick for my rifle and too difficult to get down the barrel.