Building your own gun can be a rewarding and therapeutic pastime. Most gun kits provide the barrel and lock parts, while requiring you to build the stock and assemble all of the pieces. However, the true DIYer can make every piece of a gun from scratch with enough ingenuity. As one of, if not the most important part of a gun, the barrel is an integral part of the overall gun making process and thus a good place to start your gun making adventure.
Cut a piece of thick-walled (.25 inches or more thick) iron pipe to your desired length. Make sure the diameter of the pipe fits your bullet snugly, as too tight of a diameter runs the risk of blowing the gun up, while too loose is not as accurate.
Mount the pipe on the lathe and find a metal scribe that has approximately eight teeth. This will give you eight evenly spaced rifle grooves in the barrel. Set up your lathe so that there is only one dull twist of the scribe every 28 inches; most black powder weapons have this twist or slower. Run the scribe through the pipe two to three times in succession to make sure the grooves are deep and smooth.
Use another scribe to machine threads into one end of the barrel so it will screw into its end plug. Run a deburring head through the barrel and threads. Use sand paper to smooth down the outside of the barrel and prepare it for dyeing.
"Blue" the barrel using a dye kit from any outdoor retailer. Let dry for at least 24 hours and move on to the next phase of gun construction.
Have an experienced machinist help with this project and be patient. This is a slow but rewarding process.
Test fire your gun by itself first to make sure any problems are worked out and no safety issues exist.