You Can 3D Print A Heavy-Caliber Gun -- And It's Totally Legal

(CBS SF) -- With a 3D printer and enough thermoplastic, you can mass produce plastic assault rifles from the convenience of your own home without going through a rigorous background check.

Advanced 3D-printing technology now allows for people to make durable guns. And as far as current federal laws are concerned, it's totally legal.

Medium writer Keith Mizokami documented his experience building not just any regular firearm, but a full-on assault rifle.

All it took was three hours and some light tools.

"I was an AR-15 grease monkey," Mizokami wrote. "During the course of several projects, I'd built an entire rifle from scratch. But I'd never built the lower receiver of an AR-15. By U.S. government standards, I'd be manufacturing a firearm."

The missing 20 percent he needed to make a functioning assault rifle is controlled by the Bureau of Alcohol, Tobacco and Firearms. Buying what's known as the lower receiver requires a background check. You can build your own, free from government oversight, but it's a tedious process that requires expert knowledge and precision.

Now, a group dedicated to 3D-printing firearms announced the development of a design for a Colt CM901 rifle's lower receiver -- and it's available for download off the Internet.

For those who haven't picked up an assault rifle in the last few years, this Colt is a big, powerful weapon that has a design allowing soldiers to swap out parts, including the "lower receiver" which allows the weapon to fire various sizes of ammunition.

Colt writes, the "CM901 is a multi-caliber platform that offers the modern warfigher much needed versatility without sacrificing function."

The group PrintedFirearm.com used a $500 XYZ Da Vinci printer--which is cheap compared to most 3D printers--to build the lower portion that loads and fires the bullets.

CM901 is a step above the AR-15, capable of firing the more powerful 7.62 millimeter bullet for greater range and killing power.

A video shows the thermoplastic gun undergoing a few seconds of rapid fire, but it's not clear if the lower receiver would hold up for any longer than that.

Regardless, printing lower receivers is a huge step for gun enthusiasts looking to simplify the gun building process in their own home, completely undetected by the government.