A man has figured out a way to create a 3D-printed gun that can fire actual bullets, a step toward weapons printed at home.

Michael Crumling, a 25-year-old machinist in York, Pa., said he has figured out a way to print a weapon that can contain an explosive blast by encasing the round itself in metal, according to a Wired report.

Ever since the possibility of 3D-printed guns has been raised, many doubted the idea, as cheap plastic material can’t contain the explosive force of a bullet. But by putting the ammunication in a thicker steel shell with a bullet inserted an inch inside, the bullet’s explosion won’t transfer to the plastic body or barrel of the gun.

The development allows the home-printed gun to be fired repeatedly without cracking or deformation, despite being made from very cheap materials.

The drawback is that the design can’t easily be replicated because the rounds are individually machined, but it marks a step forward to practical printed guns.

Crumling said he actually fired 19 rounds from a gun of this design used a $400 Printrbot printer.

However, the weapon is not entirely printed. He had to use some metal screws and an AR-15 trigger and firing hammer, which cost him about $30. The gun had a few misfires, but didn’t cause any internal damage in the weapon.

Crumling believes the weapon could be made semi-automatic if someone were to add revolved components and an auto-loading mechanism. He said that is the main reason he started building the weapon.

Law enforcement agencies are wary of such 3D printed weapons, which would place guns in the hands of anyone for an extremely low cost. There is also th econcern about their safety and reliability.