There are plenty of ways to "do" things without a lathe. When I was a kid, I watched/assisted my uncle in cutting a larger hole through a propeller so it would fit his boats shaft. He used a piece of oak and a cutter forged from a piece of an old rasp. We coated things up with old drain oil and hand turned the wood. I kept brushing the oil on it as He and my cousin turned the wood. We cut the Prop hole to the proper size in a little over an hour. He then fashioned a reamer out of an old piece of pipe and a chunk of that rasp and had it reamed mirror smooth in very little time. A golf ball mortar can be bored to depth with a electric hand drill and then the hole "widened" using a home made cutter and hand turning it if necessary. Or just buy the proper size drill bit and hand turn with a t handle, if your drill isn't large enough. Some where around here, I have a small cannon that was hand bored in a chunk of bronze.
Polishing the bore can be done with a piece of rod and emery cloth, cut a slot across the end and wrap some emery cloth around it and spin it like a hone with an electric drill. In a pinch I have even used a stout cleaning shot gun cleaning rod and wrapped a thin strip of aluminum oxide paper through the loop.
I dislike anything that fits a tube to a pressed, welded or bolted breech.
Near Gettysburg, PA a few years ago at a family picnic, a guy was "making noise" with his home made cannon. It blew up for whatever reason and a family member was killed. The poor guy was charged with some sort of negligent homicide and spent a couple yrs in jail.
