I hunt muzzle loader on occasion and I think you made the right choice. Close or not, with a non-jacketed lead bullet from a muzz, even @ 400+ gr, I think its risky. Modern cartridges are core bonded, jacketed, controlled expansion, ect. . Sabot's, maxi-balls, ball rounds, just arent on the same level as a modern cartridge.
Point #2 - With a muzz, the round is slowing down as it leaves the barrel, opposite of the mod firearm. Deflection is uncontrolable at any distance with a lower velocity/ft.lbs, and un-controlled expansion its even harder to put a perfect shot on anything behind brush
I heard a story in Whitefish Mt. about a muzz hunter that tried to shoot through brush at a buck. He said they filmed it, and when they looked at the footage, he hit the buck in the high shoulder and watch the round trace the spine outside of the skin. Needless to say they didnt take that buck home, they couldnt find blood or the buck, and he had to live with the fact he prob. wounded that buck