American 3D printing anarchists Defense Distributed have caused a bit of a flap in media and official circles with the release of the Liberator, a 3D-printable handgun. But how disruptive is this thing really?
What is the Liberator?
It’s a single shot handgun, completely 3D fabbed from plastic except for a metal firing pin (aka: a nail). The model demonstated so far was in .380 calibre. It’s the spiritual descendant of nasty self-maiming tools the FP-45 Liberator and the Deer gun. The manufacturers claim that it democratises access to firearms, by allowing anybody to fabricate a real gun at home. I’m going to tell you why that is a really, really bad idea.
Can you make a gun out of plastic?
While many modern firearms do make extensive use of polymers, they use tough high-impact plastics properly formed by processes like injection moulding that guarantee strength. They don’t use 3d printing, for a good reason. Crucially, they also don’t use plastic for any of the actual working parts of the weapon exposed to high stresses.
The Liberator has a plastic frame and trigger mechanism, which is absolutely fine IMO. Unfortunately it also has a plastic barrel and chamber, which is just stupid. This is made worse by the fact that’s it’s constructed using additive manufacturing (aka 3D printing) where parts are built up by extruding layers of thermoplastic. This combination of process and materials is inherently weak, meaning the weapon will be inaccurate, underpowered and dangerous to use.
Inaccurate and underpowered
Firearms are gas-operated. When the primer of a cartridge is struck it burns the propellant inside the cartridge and this generates expanding gas. This gas pushes the bullet out of the cartridge and down the bore, where spin is imparted to stabilise it once it leaves the barrel.
The Liberator’s plastic chamber is in fact more elastic than the brass of the cartridge it holds (brass elastic modulus = 100+GPa, ABS = 2.3GPa) so the chamber will not restrain expansion of the brass due to the rising pressure of the burning propellant. In a normal firearm the brass cartridge and lead bullet are constrained by the much less elastic steel chamber. This process is called obturation and is important for forming a tight gas seal so that as much energy as possible is imparted to the projectile.
On top of this, the Liberator’s extremely short barrel means that any gases that do start pushing the bullet along the bore will only have a very short time to transfer energy. Short barrels result in lower muzzle velocities, and since stopping power (ie: kinetic energy) is proportional to the square of velocity this means that short barreled firearms lack stopping power. Half the muzzle velocity will only carry one quarter the kinetic energy. And the Liberator’s barrel is really, really short, robbing the .380 cartridge of any stopping power.
It’s interesting to note that Defense Distributed have not published any chrono readings from their test firings. Were they to so I suspect you would find the Liberator is severely underpowered and dangerously useless for self-defence. Or crime, for that matter.
To make matters even worse the barrel is unrifled, and even if it were rifled the soft plastic would be unable to cut into a soft bullet to impart spin. This means the bullet emerges slowly in a pretty random direction, probably starts tumbling all over the place, and goes anywhere except where you’re pointing it. Not too useful given that you only get one shot.
But a crap gun still beats a knife right?
It should be noted that the original FP-45 Liberator from WWII (built to a higher spec than this one) was estimated to have an maximum range of no more than 25ft, and effective range was more like 10 feet. That’s about spitting distance. Police forces teach their officers that a knife-wielding attacker is dangerous to a gun-wielding cop at around 21ft, a figure the Mythbusters seem to have backed up with some playing around of their own.
Bottom line, the Liberator is no more effective than a knife, and probably somewhat less than an axe, a baseball bat, or any number of seriously lethal devices you can pick up completely legally, such as a chainsaw. Besides not being able to actually do its job, there’s a strong likelihood that it’ll blow up and plant bits of plastic in your eyes and face when you pull the trigger. Indeed, when Defense Distributed tried to fire a rifle calibre cartridge (5.7x28mm) from one it blew up on the first shot, which just goes to show these jokers have no idea what they’re doing. Did they even run the numbers on the chamber pressures before building it? I’m guessing not.
Should it be banned?
Not because it subverts firearms laws or allows criminals to tool up. Personally I’d be quite happy with criminals 3d printing themselves a Liberator if it meant they ween’t carrying better weapons, such a knife (or maybe a spoon).
However, I predict that some fool will fab one and injure themselves badly with it very soon. It’s dangerous to fire and good only for making a loud noise. You could build a more effective weapon with hardware from your local DIY store. 3D printing mongs Defense Distributed claim this gun is a revolution in civilian access to firearms. If that’s true then Lego is a revolution in building houses.
By all means, download and print one for a laugh if you want, but whatever you do don’t fire it.