A friend of mine recently had an old rifle restored and wants to try shooting it now.
It is of Belgian Manufacture, percussion cap, probably sometime around 1860 and came up to remarkably good condition.

The barrel is 51.9" at the lands, hexagonal, but also rifled. I don't mean that the external profile of the barrel is hexagonal, the inside, however I wasn't aware that this system was used in conjunction with rifled grooved within the hexagonal contours. It also has 13.2mm stamped on the barrel, so I presume that was the nominal caliber.

Where can we get a mold made up and what kind of slug is it likely to shoot best?

Thanks.

Just a thought-You may want to do a web search for Whitworth Rifle. I believe this Briitish firearm used a hexagonal bullet.