I second the mortar for a first gun. But look around. Talk to friends. Things to look for are, steel bar stubs, botche balls, seamless tubes, hydraulic cylinders, hi pressure tanks and such. If you find the right combination, you can build something for very little money. If you go to a cannon shoot. You will see 5 mortars for every howitzer. There are reasons for this. Including cost, time and transportation. Hang in there and enjoy the build. It's part of the fun.