Michael Crumling, a 25-year-old machinist from York, Pennsylvania, has developed a round designed specifically to be fired from 3-D printed guns. His ammunition uses a thicker steel shell with a lead bullet inserted an inch inside, deep enough that the shell can contain the explosion of the round’s gunpowder instead of transferring that force to the plastic body or barrel of the gun. Crumling says that allows a home-printed firearm made from even the cheapest materials to be fired again and again without cracking or deformation. And while his design isn’t easily replicated because the rounds must be individually machined for now, it may represent another step towards durable, practical, printed guns—even semi-automatic ones.
“It’s a really simple concept: It’s kind of a barrel integrated into the shell, so to speak,” says Crumling. “Basically it removes all the stresses and pressures from the 3-D printed parts. You should be able to fire an unlimited number of shots through the gun without replacing any parts other than the shell.”