YOur barrel was designed to shoot plastic shoes and .50 or .45 caliber bullets, Not conicals. They may or may not shoot well in that fast a rate of twist.
As for shooting round ball, just use less powder. Start with 35 grains and work up by 5 grains to about 50 max. to see what give the best accuracy. YOu are going to plink, and target shoot with the RB, and hunt with your conicals. The RBs will be much cheaper, and will encourage you to shoot more. If you can, trade that barrel off for something designed to shoot round ball. The Round ball has been killing deer for as long as we have had guns( 500+ years) and those folks pushing these new guns and telling everyone that the Round Ball is ineffective and cruel to animals obviously don't know what they are talking about, or have a commercial interest in their lies. ( Toby Bridges comes to mind.) Finally, no matter what you shoot, you are not going to create a 200 yard rifle. Forget that bit of nonsense. White tail deer hunting is basically a 50 yard deal, in spite of all those long range shot stories you read in the hunting magazines. Ardhers routinely kill deer at under 25 yards. My closest shot was a about 6 feet! ( 2 yards) My longest shot to date has been a little less than 40 yards. Deer are cautious creatures, and only during the night do they venture out into open fields, or during the rut. Otherwise, they stay in wooded areas, in tall grass, or in ditches and creek bottoms, where they are out of sight, but can use their ears and nose to alert them to approaching hunters.
I think people who buy guns to " qualify " to hunt in special Muzzle Loading seasons, but refuse to learn how to hunt, and understand the challenges that restricting yourself to using Traditional ML rifles and Smoothbores for this kind of hunting place on your hunt, drives most of us tradional ML shooters nuts! If you want to shoot deer with some gun that shoots flat to 200 yards, Get a regular season permit for modern rifles and have at it. Stay the heck out of our ML only seasons, where we are working a lot harder to fill a tag! The satisfaction we get taking a deer with a firearm that is similar to that used more than 150 years ago adds to the pride all hunters take in successfully taking any deer. Taking a deer with a tradional Bow and Arrow, rather than with something that looks like an escapee from a spaghetti factory with wheels, also adds to the pride of accomplishment for traditional archers.
If that is not the experience you want to have, then please buy another gun and stick to the regular gun season when you hunt.
