I have long suggested practical homemade guns of the future will only use 3D printing as part of the process. They will be hybrid designs using the strengths of 3D printing and simple metal components to produce practical firearms in the home or in small, unregulated shops.A prominent experimenter of homemade and small shop technology for crafting usable guns, Ivan the Troll (Internet screen name) claims to have made a breakthrough in home manufacture of rifled barrels. Ivan is part of, and often the spokesperson for, the Deterrence Dispensed project. Rifling a barrel has been done for hundreds of...