Nick it will most likely not shoot both barrels to the same point of aim with a modern shell. There have been a couple of articles written in Double Gun Journal about these guns. I've owned two. The first thing that you need to determine is the rate of twist. This will tell you if the gun was made for round ball or conical bullets. Next the weight of the gun will tell you if it was made for light or heavy loads. Try and find the articles I believe they were written by Mr. Bell. Good luck.