Answer:
Depending on the type of gun used they can shoot in excess of 1000 yards. Most rifled muzzle loaders are accurate up to 300 +/- yards. Muskets, or guns without rifling are able to shoot accurately to about 150 yards +/- though longer shots have been recorded in all cases, the guns used were designed for long range shooting. There is a wealth of information available at the long range muzzle loader forum posted in the related links section of this answer.