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Topical TV

Print Your Own Guns


Surfing channels tonight looking for something new to watch ... flipped onto a new episode of CSI-NY just after it began. In the scene, the detectives find the body, shot through the heart. A few feet away are computer cables but no PC, and a dirty table with a clean spot in the middle, surrounded by piles of what looks like dust or dirt. “And what was here?” asks one CSI, “his printer?”

And with that, I had the whole mystery solved. 1 minute into the show.



They were doing the print-a-gun thing. Very topical. I’m doing the old eye-roll expecting more idiotic “TV science” like the episode they did a while back with the homing bullet that managed to reverse it’s own flight path while being fired and still inside the gun barrel.

But, actually, they went about it mostly right. I don’t think you could use this technology to print an assembled firearm. You could print the parts, and then put them all together. And I have real doubts that the device can print a coil spring that actually works as a coil spring. But I’ll allow Hollywood some slack this time, because they had the grace to do the shooting part in a way I’d agree was feasible.

The guy used his computer and a special metal powder 3-D printer to build himself a .38 Special revolver. Ok, it’s a S&W model 642, but that’s not important. What’s important is that it’s a .38 Special, which is one of the lowest pressure “modern” cartridges out there. And no ammo company sells ammo loaded right up to maximum pressures (duh, lawyers!). And since it was a revolver, there’s that gap between the front of the cylinder and the back end of the barrel, which is usually about 0.0035”. That lets some of the powder gases (and some of the bullet too!) squirt sideways out of the gun when it gets fired (which is why the police shows are always checking the suspect’s hands for “GSR"). If the gap is bigger, more gas escapes, and bullet velocity drops. But velocity drops because pressure is lower. So we’ve got a low pressure cartridge being fired in an even lower pressure environment.

And the producers tried to create a mystery by showing us bullets with no “ballistics” on them - no rifling engraving. In other words, the pistol was a smoothbore. A tube. And if it wasn’t exactly the world’s tightest fit, bullet wobbling down the barrel on firing and all that, then once again there would be far less pressure. Would it be accurate? Hell no. But it was only used at a distance of 2 feet, so that doesn’t matter. The bullet would tumble too, “keyhole” is the shooter’s term, if it was loose in the barrel or not stabilized by the rifling. But that happens at 25 feet or so. At 2 feet you’d never know. But now we’re talking even lower pressures.

And they went out of their way to have the lab guys discussing how the guy who had built the gun had then oven cured it for some time. I’m pretty sure that’s what you’d have to do even with a laser sintered metal form as depicted in this episode; it’s just powdered steel and epoxy dust, so you’d have to heat cure the glue over time. The laser just gets it hot enough to barely stick together while printing.

So the bad guy gets the gun, loads a round, and shoots the fellow who designed it and built it.  Then he gets another round, and shoots the lawyer his ex-wife used in their divorce. And while he kills that guy too, the gun blows up in his hand and injures him with shrapnel. The CSIs track him down through hospital records (so much for patient privacy, huh?) and bust him. Case closed.

But I will give the producers a respectful tip of the old hat, because for once they’ve done a pretty decent job with something concerning firearms. They found a scenario where this just might work. What the guy built on the show was little more than a zip gun, but zip guns can still be lethal. I still think that a printed gun will still blow up on the first firing no matter what, but you might get a poorly designed one with big cylinder gaps and over sized bore to last two, maybe three or four shots. Let’s go for two as being at least plausible. And that’s what CSI-NY did.

Now, should we all wet our pants in panic and demand pre-emptive laws about such a thing? Hell no. Do you have any idea what a 3D printer costs? Cha-ching bay-bay. Mucho. No criminal will ever bother; it’s much easier to steal a real gun or to buy one on the street. And it’s no crime for any US citizen to build their own firearms at home. Seriously. It’s legal. Just don’t even think about trying to sell one of them. That’s when 10 truckloads of laws, permits, MIB, licenses, regulations, zoning, and black helicopters come into play.

And they’re always going to blow up on the first or second shot, no matter what. So don’t bother. Now, if you happened to have a CNC milling machine in your basement and some 4150 bar steel and a gas forge and some case hardening powder



Posted by Drew458    United States   on 01/04/2013 at 10:01 PM   
 
  1. Awhile back, I saw a special which showed how comedian Jeff Dunham made his latest dummy (Achmed Junior) using a CAD program and a plastics printer. Thing took hours to print the head, but it was almost ready to be painted and start talking when he was done - just need the eyes and speaking mechanism.

    Soon, there will be no need to go shopping - you’ll just print what you want. Not sure how they’re going to handle biological items like food - but eventually Geeks will be able to print real girl friends!

    Posted by jackal40    United States   01/05/2013  at  07:17 AM  
  2. That,s funny because my friend has a cnc mill in his garage for hotrod work and we use 4150 on a rare occasion for piston pins and such but your right that its way more trouble than its worth to invest the time for a damn gun.

    Posted by Rich K    United States   01/05/2013  at  09:41 AM  
  3. 3D printers are getting cheaper all the time. I’ve even seen some home-built versions. You just need the parts from a couple of old scanners and a microcontroller board like the Arduino. I’ve not seen one of those do the metal sintering process though… mostly they use melting plastic.
    I saw a youtube vid of one of those printers printing a crescent wrench prototype, complete with moving parts. Not practical, but cool.

    Posted by JimS    United States   01/05/2013  at  01:46 PM  
  4. Exactly - they can make you a parts prototype, but not the real thing.

    Posted by Drew458    United States   01/05/2013  at  03:35 PM  
  5. Well, I imagine for some products, like those made from plastics, you could produce the real thing from a 3d printer.

    Posted by JimS    United States   01/05/2013  at  05:33 PM  
  6. I would use a 3D printer to make a model as in ‘lost wax’ casting. The process is 1) print a wax or plastic model with sprues added 2) Dip the model in a ceramic slurry, let dry, dip, let dry, repeat until a ceramic shell has been created around the wax. 3) Fire the mould in a kiln at high temperature (around 1600C) the mould is positioned so that the wax or plastic will drain out the bottom sprue early in the firing process 4) With the mould still hot, pour molten steel in through the top sprue and let cool. 5) Chip off ceramic from steel casting, cut off sprues, finish machine and heat treat.

    Ruger firearms have been using this technique to make receivers and internal parts since the 1960s. This reduced the need for extensive machining which made Ruger’s guns less expensive to build without reducing quality.

    Consider this. The Pennsylvania rifles used by minutemen during the American Revolution were all hand-made including the rifling. With a credit card and a phone you can have better machinery and better steel than Samuel Colt or John Moses Browning had delivered to your door. The only hard part of building a gun is the rifling and there are several youtube videos showing how to build them.

    Posted by Al_in_Ottawa    United States   01/05/2013  at  10:34 PM  
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