Leupold have launched a new scope called the UltimateSlam for shotguns and modern muzzleloaders. The SABR reticle can be adjusted to match your load.
SABR: Sabot Ballistics Reticle
Leupold’s® all-new UltimateSlam™ riflescope is the ideal combination of flexibility, accuracy, and durability for today’s modern muzzleloaders and shotguns. As an example of accuracy, using Hornady SST 2-pellet, 3-pellet and 12 gauge shotgun loads at up to 300 yards, the maximum error of the UltimateSlam is less than 1″ as compared to a 14″ error from the leading competitor.
More info here.