gumboman,
Danny Caywood offers a jug choking service. I don't have any firsthand experience with his work, but some google searches will give you an idea of the results that you might expect. Also, I don't know what you want to do with this gun but a Colerain 20 gage turkey choke barrel loaded with 2 ounces of shot and 100 grains of powder shoots as tight a pattern as I have seen from any shotgun. I agree totally with smallpatch regarding the shorter barrel length and running or flying game. I am a rookie with this gun and moving critters, but I wish I had my rabbit hunting experience caught on video, it would have bee hilarious to watch. Grinslade's Flintlock Fowler book is a great reference if you are interested in historic guns, or placing a design in a specific time period or location of origin.
Tiswell