In Neal's "Great British Gunmakers 1540-1740", there are photos of a wheellock pistol (inside and out) that has the pyrite coming at the wheel horizontally, from the front. Apparently this was done because it was a double barrel, over/under, and the maker wanted to keep the overall height down. Interesting design. The wheel rotates counterclockwise, so the sparks are thrown up, away from the primer. The pyrite is inside a box that keeps the sparks confined to the pan.
It would be a fun one to build.
It would be a fun one to build.