When Fort Macon was built, the intention was to mount a carronade in each of the casemates. This would have been to fire on any attacking party that had made it into the dry moat, as it would have been nearly impossible to aim any sort of cannon at such an angle as to fire above the lip of the outer wall.

These carronades were never installed, but beneath the opening of each casemate is a horizontal opening just above the floor. The carriage of a carronade would have extended into this triangular opening, and locked into place with an iron pin, which would enable the gun to be swiveled from side to side. Fort Macon expert Paul Branch tells me that there was no exterior barrack, and since soldiers stationed at the fort had to live in the casemates, there was really no room for the carronades anyway.