You keep saying that but being designed for and actually doing it are 2 different things. Just dumping max charges and a bullet down the bore and then thinking that's the best accuracy it can get is nothing less than foolhardy. You should know as well as I that not all rifles are equal. What shoots best out of one may not be the case with another regardless of the brand or model.
Encore I understand that that you have a vast knowledge shooting muzzleloaders but don't be blind to what I am saying. Being desinged to shoot heavy charges accurately does not mean every rifle can do it. Some may reqire a lesser charge for utmost performance.
The OP stated that he is going to use the rifle mostly for deer hunting. To that end 100 gr V of BH209 will kill a deer just as dead as 120 gr and if the accuracy using 100 gr is better then its a win win.
I am not blind to what you're saying. Not at all. But again I'll tell you this, with the recommended charge,
HE IS NOT SHOOTING A MAXIMUM CHARGE! THE RIFLE IS CAPABLE OF MUCH HEAVIER CHARGES. He could be shooting 200grs of BP or substitutes, so the suggestion I gave him is the AVERAGE of what all other owners are shooting and achieving the best accuracy with the 320gr Fury bullets and BH209. Don't believe me? Contact Dennis at Fury and ask him. Or, if you have FB, go to either of the sites and read what owners are using.
I'm sorry but the fact is, you don't understand the UF or RUM rifles. Believe me, I do. I've shot many thousands of rounds through them. These rifles are one of the few, that if you load them as suggested, they can be extremely accurate right out of the box. I'm very familiar with the rifles, having been close friends with the person that invented the UF, Ken Johnston. Ken and I were friends when Remington purchased the rights for his ignition system. I know the rifles like the back of my hand.
As I mentioned earlier, the rifle can be accurate with a lesser charge, or even a heavier charge. But again, no one has shot these rifles more than myself, short of maybe Randy. I KNOW what works and how it works with them. The OP has a 500yd hunting rifle. Now his abilities are another story.
We're not talking CVA, Traditions, Knight, or TC rifles. We're not discussing rather one uses 75grW or 80grs of BP or Subs and/or rather those charges will harvest an animal.