120 grains of loose Triple Se7en and that projectile like already stated... I would consider that a max load. You will know when you fire it and check the accuracy. As for the projectile, if any of them will hold with that kind of power behind them that dead center 300 grain will. I shot them in my Black Diamond XR with 120 grains of Pyrodex and the accuracy was excellent. That would be a real long range load in my opinion.

Be sure and keep an eye on your breech plug for seizing.....

Read your owners manual. Many times they place a limit on the size of sabots or conicals they want you shooting out of your rifle.... CVA has limits.