I built a much more primitive version, a scrapyard special if you will. I used a threaded breech with a male stud that accepts a percussion cap. Press cap on stud fill breech with 500 gr of 1F, install breech, drop projectile down tube...ka whump. I used beverage cans filled with cement. Great accuracy, I once had a 100 yard, 3 shot group. Fish ducks hated my 'mortar'. All things are possible with a scrap pile and a lathe.
