A D.I.Y. semi-automatic rifle, brought to you man behind 3D-printed handgun

The creator of the world's first 3D plastic handgun has unveiled his latest invention: a pre-programmed metal-milling machine that enables anyone to easily make the core component of a semi-automatic rifle.

Within a matter of hours on Wednesday, libertarian Cody Wilson of Austin, Texas had collected more than 40 pre-orders for the computer-controlled Ghost Gunner, which his firm Defense Distributed is selling online for US$1,199.

"I'd say it's a desktop machine that can mill aluminium," Wilson said by email when asked to describe the black cube device in layman's terms. "We've programmed it to easily mill guns for the uninitiated user."

Wilson whipped up a furore last year with the Liberator, a single-shot, all-plastic handgun that anyone could make with a simple 3D printer. The US State Department forced him to pull the blueprints off the internet, but not before copies appeared on offshore file-sharing websites.

The Ghost Gunner is programmed to mill the lower receiver of an AR-15 type rifle - the key section that holds the weapon's moving parts, such as the trigger, firing pin and magazine.

A promotional video shows the plug-and-play device - which ships with software and instructions - carving a lower receiver out of a block of aluminium with a mechanical burr.