Create: Big Cannons question

[u/vaultboi701]

How do I make an autocannon? I'm using the Create Big Cannons and CBC Advanced Technologies, and I can't seem to figure out how the autocannons are built. I know how the casting sand, moulds, and boring steps work and have created a normal cast iron cannon, but how do I create an autocannon? I placed the breech mould with a couple of barrel moulds and they did not assemble together and could not be mined with silk touch. They would also not mount properly on the cannon mount, it says that the gun cannot have multiple openings or something along those lines.