Here are 2 project 1/2 scale medieval guns. The barrels were made from oil well tubing, and the breech plugs are pinned and welded in. Here is the pile of lumber I used for one of the carriages:
Here are the finished pieces. The one with the big wheels was built by George Silva, who is a retired movie prop builder and armorer for Paramount Studios.
I shoot #4 sinkers, lightly patched, and about 250 grains of fg powder to send them projectiles down range. They are about 4 feet in length. With the wheels being removable, they can be put into my Scion xB and transported easily.