First off let me welcome you to the forum..

300 yards with any rifle is a long way. Even centerfire rifles. If any muzzleloader was going to do it, I would guess that the Pro Hunter might be one of them. Personally I think people are trying to push a muzzleloader too far.

When people ask me about how far they think their rifle is good for, I normally tell them with good optics, 200 yards in not out of the question and that will take some practice and load development.

If I really had to get a muzzleloader and shoot 300 yards, then I would look at; Savage ML-10II,Omega, Pro Hunter, Encore, Knight Long Range Hunter, Knight Extreme, and some of the better top of the line CVA, Traditions, etc.. then I would tell you that you really should not shoot that far. Instead limit your shots to 150 yards - 200 yards max. Although there are people that can and do shoot further then that.

I am not one of them.