When I was very young, maybe fourth or fifth grade in grammar school, my buddy and I built us a pistol. We referred to it as a "pirate's pistol."
Using a coping saw, we cut some semblance of a stock out of the end of an orange crate. (Orange crates supplied most of our toys. The ends and center partition were 3/4" wood, sides and bottom 1/4" wood. Crates were free for the asking at the neighborhood grocery store.)
The barrel was 1/2" copper tubing we found in the garage, along with a soldered on cap. Thin gage galvanized sheet metal bands attached the barrel to the stock. With nails and rods, we attached a trigger and spring to the stock. More sheet metal and we had a trigger guard. The hammer posed a problem. It would not hit the end of the barrel. (These parts were salvaged from cap-pistols) As we tried to bend it, it broke in two. After a search, we located a hammer with the right crook to it.
We drilled a small touch hole in the barrel breech, using an old hand drill. We had a supply of steel ball bearings for bullets, which took newspaper wadding to patch. We had a .38 S&W cartridge cas for a measure to measure out the blackpowder. Taping a paper cap over the touch hole readied us for firing.
The first shot hit our target board, a piece of 1 x 12 pine maybe three feet long. And penetrated it, too. So too, did the second shot. On the third shot, I felt the gun kick sidways, and saw no hit.
Our commode pipe barrel had let go. Too dumb to be scared, we thought about barrel replacement, but finally gave up on the whole project.