Rifles & Bullets Are All Different...
Bruce is right, more details about the rifle would help in suggesting a good bullet.
Most modern in-lines, not all but most, have a turn-in-28 inches rifling twist, and saboted .451-.452" dia. bullets of 250- to 300-grain tend to be best performers out of the popular .50 caliber bore. I recently started shooting a T/C Triumph (1-in-28 twist)...and the rifle shoots well with a variety of saboted bullets.
For an elk hunt in the Bob Marshall Wilderness Area of western Montana the middle of next month, I've settled on a 120-grain charge of Blackhorn 209 and the saboted .451" Scorpion PT Gold bullet by Harvester Muzzleloading. This combo shoots great out of the rifle. I tweaked the rifle and load just a couple of days ago...and the 100-yard group I shot before heading home measures barely .500" center-to-center.
This load is good for 2,068 f.p.s. at the muzzle...and 2,850 f.p.e. At 100 yards, it still hits with more than 2,000 f.p.e. - and all the way out at 200 yards, it would hit with 1,500 foot pounds of retained energy.
I'll also be carrying one of Montana's first wolf tags...and would love to be the first hunter in the coutnry to legally shoot a wolf with a muzzleloader.