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Can You Build a Plastic Gun?

May 10, 2013

liberator-plastic-gunThe State Department told Defense Distributed to stop releasing plans for its plastic gun made with a 3D printer.  That is silly.  Any competent mechanical designer could build, and any third world dictator could buy, a weapon that is hard to find with x-ray machines or metal detectors.  The weapon could be detected by advance imaging techniques and pattern recognition equipment, but small airports don’t have those machines.  None of this is news.  The latest action by the US government is simply more security theater.  The real question is how much money does a terrorist group want to spend to get a weapon past security.  Two thousand people were killed and the World Trade Center building was brought down for a few thousand dollars and $3 box cutters.  Even today, the aircraft cleaners and baggage handlers are often uncleared and working for third-party contractors.  They steal I-pads and don’t make much money.  They can be bribed or blackmailed.  Why do we see this security theater at this time given those facts?

We pretend that we can control violence by controlling the tools of violence.  The recently publicized case of the 3D printed plastic gun is noteworthy because 3D printing demands so little technical knowledge.  What took a competent first-world engineer $50k can now be done almost anywhere in the world for $30k.  The first gun is $30k; the next one is $40.  It would take more money to design non-metallic ammunition, where the primer/percussion cap is the hard part to solve.  I’m not going to go into details here, other than to say it can be built by conventional means rather than using 3D printing.

It is not difficult to design a one-shot firearm and we use 3D printers every day.  You won’t stop a dedicated designer by outlawing 3D printers.  Gun free zones were always a joke to the average machinist or student of history.  Now they are a joke to everyone else as well.  Printed weapons are not good guns, but they work for a few shots.

What is involved in building such a weapon?  You would design a non-metallic gun rather than execute the design of a metal gun in plastic.  The hobbyist uses plastic because the 3D printer is versatile.  The terrorist chooses plastic because some plastics don’t show on conventional x-ray machines.  Ignoring the ammunition, you can easily build a smooth-bore gun.  You can also build an accurate gun that spins the projectile by using polygonal rifling and polygonal bullets.  It was done a hundred years ago.  Let’s look at the problem of an undetectable gun and home-made gun one piece at a time. 

  • Likely candidates for the frame are molded or machined epoxy with Kevlar or carbon reinforcement.  The glass in fiberglass shows up slightly with x-ray scans, but there are alternative materials.   You could almost use wood and epoxy if you’re a green terrorist, but plastics are less visible by x-rays.
  • Use machined nylon or polycarbonate plastic for the internal components.
  • Springs can be made from laminated carbon fiber/epoxy or polycarbonate plastic.
  • The hammer can be cast from silicon-carbide in epoxy.
  • The firing pin could be an alumina rod or silicon-carbide/carbon fiber tube.
  • The barrel could be a polycarbonate/ fiber composite.  The liner is an engineering plastic with an over-mold of tensioned carbon fiber/Kevlar.  The high-tech version is rifled with a twisted hexagonal internal diameter.
  • You don’t need a cartridge if you build a muzzle loading firearm.  You could use an engineering plastic to machine your custom cartridge cases if you want cased ammunition.
  • Projectile can be made from epoxy molded silicon, silicon-carbide or alumina.  It is easier to use a silicon-carbide slug if you’re using a smooth bore.  Coat the bullet with Teflon.

The real cost is not for the firearm, but to bribe third-world airport officials so you can get a test-look and see what your weapon looks like on airport scanners.  The recent political theater is for the new media and the low information reader.

Designing a semi-automatic firearm is harder.. but could be done.

Now, tell me again why you believe in gun control?




Rob the design engineer

6 Comments leave one →
  1. Dave permalink
    May 10, 2013 3:54 pm

    Can’t stop the signal…


  2. WAIN permalink
    May 13, 2013 5:23 pm

    I know severl competent machinist. And I am sure that this could be done with only a drill press and some hand tools.


  3. KA9VSZ permalink
    May 16, 2013 2:22 pm

    Were the nested bearing components printed separately and then assembled or printed as one unit or other?


    • May 16, 2013 2:41 pm

      Printed in one assembly. You can put a ball inside a hollow box with solid walls. Sometimes you need a vent to wash out an inert spacer material used during fabrication.

      To speed assembly time we will glue sections together.


  4. KA9VSZ permalink
    May 16, 2013 2:48 pm

    Wait, does “You can put a ball inside a hollow box with solid walls.” mean you can print a box with a ball inside it in one go? Not printing a box part-way then dropping the ball in? If so, OMG, I’m living in the future.


  5. May 16, 2013 2:50 pm

    Welcome to the future.


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