I never shot muzzleloaders out to 200 yards so this is a tough one. It might be my Renegade with my .45 caliber GMB shooting 200 grain Shockwaves. It shoots them very accurate. I'd change out for the Nikon 3-9x40 Omega scope I have, just to get a better view. Off hand he might have me but off sticks I'd give him a run for his money.
The other rifle that shows a lot of promise is the White Model M97 in .504 Ultra Mag. It shoots the 460 grain conical bullets very accurate out to 100 yards. I think with 2 weeks to practice I could learn the drop out to 200 yards. Those big conicals should be less effected by wind gusts. With the right charge it should be able to hand this. It also has a Nikon scope already on it that is real good.