While the details of the gun are minimal, 50 cal muzzleloader, it is not unreasonable to assume a MLer projectile could go half a mile (880 yards). The 1853 enfield that was used in the cival war has a ladder type rear sight that is marked for up to 1000 + yards. The load was only 60 grains of powder and a 600+ grain bullet, the drop on the Enfield is something like 165 feet at 880 yards. The energy at half a mile would be enough to go through a couple of sheetrock walls for sure (around380 fpe). The exterior wall would be the toughest to penetrate in most houses but if it was only vinyl siding and tyvek on the exterior wall, no problem. More modern style smokepoles would shoot flatter but may not haveany more energy that the old CW style guns at that range due to lighter bullets. For instance, a 200 grain SW ahot at 2300fps (150gr load) would only drop about51 feet but would have similar energy (around 330 fpe) at half a mile.

The problem is that the shooter would have to be shooting somewhat up hill with no backstop for the bullet to go that far, or the bullethit a rock or something and went that far (I would think the energy would be much less if that happened). This is not a good practice and it is discouraged in all hunter safety courses. The shooter needs to be sent back to get or review his hunter safety certification, at the very least.