Wednesday, May 22, 2013

Why The Next 3D Printed Gun Should Be .45ACP

Earlier today, Borepatch linked to a story on Forbes about further experimentation done with a 3d printed gun, plastic barrel and all. 
One evening late last week, a Wisconsin engineer who calls himself “Joe” test-fired a new version of that handgun printed on a $1,725 Lulzbot A0-101 consumer-grade 3D printer, far cheaper than the one used by Defense Distributed. Joe, who asked that I not reveal his full name, loaded the weapon with .380 caliber rounds and fired it nine times, using a string to pull its trigger for safety.
When I first heard about the idea of printing a gun, I thought the barrel would be the hard part.  Plastics just wouldn't hold the pressure, or so I thought.  But a few weeks ago, it popped into my head that anyone knows that to make a vessel hold higher pressures, you just increase the wall thickness.  The gun might not end up looking like other guns, but it would indeed be functional.  Here's the barrel they used.  Doesn't look like your typical pistol barrel, but it worked.  This is after 8 shots.  They pulled it after that number, out of caution.  (Forbes)
 
There are limits, of course.  To make a scuba tank that would hold 70 cubic feet of air at 2000 PSI, I don't think you'd want a plastic tank the size of a small room.  Sorry - don't remember how to do the calculations off the top of my head.  (Bad blogger!  Lazy blogger!!  Why, I ought to rub your nose in your Marks Handbook!!). (Whaddaya mean schizo?  Who's schizo?  Us??)  I'm sure a real M.E. would know.

When I saw that Cody Wilson ran his first tests of the Liberator with .380, I was impressed.  I thought for sure he'd run .22LR.  But I never bothered to do what I did I today, look up chamber pressures for various common cartridges. It turns out the SAAMI chamber pressure for .22LR is 24,000 PSI, but .380 is 21,500 PSI.

And the SAAMI pressure for .45ACP is 21,000, even lower than the .380 they've already demonstrated. 
Screen capture of the "Lulz Liberator" that fired nine successive shots. 

The original FP-45 Liberator of WWII fame was .45 ACP.  Smooth bore, so it was inaccurate.  This one has a rifled barrel (you can print rifling in place!), so it has the potential to be more accurate - though bigger because of being plastic rather than sheet metal.  So what are you guys waiting for? 

13 comments:

  1. I didn't know it was rifled already. That's very promising. Have there been any quantitative accuracy trials?

    I wonder if anyone's tried a destructive test with a single barrel, and I wonder if firing rate is more important than number of rounds fired in predicting barrel failure. If you can keep the rate down that might keep the temperature down overall and tame the fatigue stress threshold somewhat.

    It's an exciting time for us gun nuts.

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    1. No accuracy tests so far. We were happy to just get chronograph results on it (just under 500 fps).

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    2. ...And bookmarked.

      Thanks for what you're doing. Looking forward to future results!

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    3. Thanks for dropping by, Have Blue. The 500 FPS number is interesting - quite a bit lower than the normal. Is there too much loss of pressure from the barrel expanding?

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  2. I'd guess that printed rifling would wear quickly? Might want pretty soft lead bullets. Reloading for this might be a good thing so as to tailor loads and lead.

    Very cool.

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  3. The original M-16 barrels were a composite barrel, small diameter steel tube with a fiberglass wrap. On air tanks, I believe the current firefighter Scott air cylinder is a composite wrapped construction.

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  4. indyjonesouthereMay 23, 2013 at 1:47 PM

    An interesting comment I read is that we should be looking at using the plastic printed parts to create sand molds from which we could cast metal parts. If someone would make a metal barrel from a printed part I think we could look at Holder or Schumer collapsing in a total sh#t fit.

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    1. Very, very possible. Jewelers have been using 3D printed models to make investment casting molds for lost wax casting - essentially the same thing, except instead of a sand mixture, it's something that looks and feels a lot like plaster of Paris (but isn't!) That's been done for years, now.


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  5. That's interesting about the pressure of the .45 ACP. Not entirely surprising, looking at the muzzle velocity. I'd expect lower velocity maps to lower pressure.

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    1. I'd expect muzzle velocity to be a product of pressure, area of the bullet and barrel length, undoubtedly with weird coefficients or other curve-fitting terms to get the units to work out right.

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  6. Of course it is going to "wear quickly."

    The original "liberator" was also a 1 shot gun. It wasn't supposed to be your weapon; it was supposed to be how you obtained a weapon - i.e. shoot that sentry in the back of the head and liberate his firearm and ammo belt.

    The point of the new version... to stick it to the Left as far as I can tell. You can make better weapons in you garage if you have some machine tools.
    http://wheelgun.blogspot.com/2007/06/homemade-weapons-part-2.html

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    1. You can make better weapons in you garage if you have some machine tools. We speak machine tools around here. Not like a 30-year experienced machinist, but enough to make some chips.

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  7. I have witten a book just being printed on a homebuilt 5 shot .45 ACP Carbine; it uses a manufactured barrel and a machine shop built "Bar Magazine" (like a revolver cylinder only a bar which ratchets through the gun and falls out the bottom when done. The other parts are done with drill press, files, angle and bench grinder and Dremel tool... and a wire welder.. garage tools. Book is 140+ pages, with 80 photos and drawings, large format 6.7" x 9.6" size.
    it will be out soon, "Homebuilt .45 ACP Carbine" and available from Amazon, bookstores, Ebay, etc.
    Thanks..
    Gary F. Hartman

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