LOL, you can own a cannon now. No permit needed. A friend of mine was going to build a reproduction civil war mountain cannon for me. Unfortunately he passed away.
He made nd sold cannons as a hobby. He dud some amazing work and incredible carriages.
The mountain howitzer is a nice cannon. Small and lightweight. We were in some reinactments with units that fielded them,
I think the carriage on a large gun is the hard part. The iron fittings are somewhat intricate and getting the wheels correct is time consuming. A 12 pounder Napoleon weighs over 1,000 lbs and the wheels must be right in order to move them.