Can't say for sure if you "need" one, I wouldn't think you'd have much to worry about unless you're really working over the muzzle crown. That said, I've heard enough horror stories of ruined accuracy caused by worn crowns (allegedly from brass/fiberglass/aluminum/steel cleaning rods) that I do use one of the plastic bore guide bushings on my rifles. Picked it up at Friendship last fall for a buck or two, but pretty sure the usual suspects will have ones that fit muzzleloader rods- Midway, Natchez, Track of the Wolf, October Country etc. Tack one on to the next order you make from any of those places, and you'll have cheap insurance against muzzle wear.