Making a semi-automatic pistol using a 3D printer and parts purchased on the net couldn't be easier. If I can do it, so can you.

You will need:

1) A 3D printer. Ideally, a big one capable of printing large objects. If not, you can print the receiver in sections and glue the pieces together with Krazy glue, super glue, or in the case of ABS, acetone weld. This is what I did the first time around.

2) Strong filament. ABS, HIPS, nylon, etc. are top choices, but believe it or not PLA works. It just doesn't last.

3) A CAD file for a Ruger 10/22 or Ruger Charger receiver. There are plenty floating around. The first pistol I made (the neon green one) used a CAD file designed by Todd Aho of Taho Designs. It was designed for CNC milling, but it worked okay with some Dremel and sandpaper fitting. The one I designed with iron (plastic) fixed sights prints ready to go. Unfortunately I cannot release it because of ITAR. Find something similar that fits with what kind of gun you're after, or design your own. Like I said, there are plenty of files floating around in the aether.

4) A full set of parts for the Ruger Charger or 10/22 (parts are compatible between the two weapons). This will include:

Barrel (1)
Bolt (1)
Charging handle / recoil spring / recoil spring guide rod assembly (1)
Fire control group or FCG (1)
FCG-receiver mating pins (2)
Large pin (1)
V-block (for barrel retention) (1)
Barrel retention bolts (2)
Stock (1)
Stock screw (1)
One set of brass balls

Get a threaded barrel if you can. This would be a great gun to use with a 3D printed silencer (all NFA rules apply - be sure to fill out a Form 1 with $200 tax stamp payable to the ATF before printing any silencers).

Step 1: Do Legal Research

Ascertain that it's legal in your area to build the sort of firearm you want.

Some suggestions:

Visit ATF.gov
Ask a local law enforcement chief
Hire an attorney specializing in firearms law
Write a letter to the ATF's Firearms Technology Branch

Step 2: Print Receiver

Print the Ruger Charger receiver vertically (standing on end) with the barrel orifice pointed upward. This will help keep the barrel channel and retention bolt holes concentric for easy installation of the barrel. Print at 100% infill with the strongest material available. If properly built, the receiver won't have to contain any pressure. It's basically just a box.

Step 3: Remove Support Material

Experienced 3D printing folks will already know how to do this. Use diagonal cutters, flush cutters, and needle-nose pliers.

Step 4: Acetone Process (optional)

Wiping the receiver down with acetone, or putting it in an acetone vapor chamber for awhile, will melt the striation lines together, creating a smooth surface finish. This may help reduce cracking, which tends to happen along the striation lines. It also may allow the bolt to slide more smoothly (although if you've sized everything correctly, this shouldn't be an issue). Optional step.

Step 5: Assemble Pistol

The Ruger Charger and 10/22 have been around forever, so there are plenty of resources online already. Just in case you have any trouble, I made you a video in which I complete the whole process before your very eyes.

Step 6: Test Fire

Get someone you don't like to hold the gun and fire it a few times, just to make sure it doesn't explode. Just kidding: it probably won't explode. But if you're concerned about that, you can always clamp it in a vise and pull the trigger with a rope. Just make sure the vise is secured well, or this could actually make things more dangerous for you... In any case, eye and ear protection are a must.

Step 7: Enjoy Your New Pistol Safely and Responsibly

Remember that all of us who design and develop printable weapons are ambassadors for our cause. As of this writing, there have been no reported injuries or deaths from 3D printed guns (despite their popularity). Let's keep it that way.

Unless somebody is trying to kill you. Then let 'em have it.