3D PRINTED GUN!

that's why you start with .22LR or something... i am not surprised that this failed. had they done any research into this they would know that it would fail and that it would fail right where it broke since dozens of guys have already done this very thing and have all experienced issues with the buffer tube.

HURRRRRRR.
 
that's why you start with .22LR or something... i am not surprised that this failed. had they done any research into this they would know that it would fail and that it would fail right where it broke since dozens of guys have already done this very thing and have all experienced issues with the buffer tube.

HURRRRRRR.

Exactly! Even the commercially available polymer lowers have had this issue because that is the weakest part of the lower receiver, and also happens to be the part that receives the most stress. It should work fine for a .22 though.
 
Would a piston upper fix the problem?
No, if anything it actually might exacerbate it even more. relocating return spring would fix the problem

i've seen aluminium lower fail in the spot where buffer tube attaches and it's a lot stronger that any plastic.
it's just quirk of Stoner's design. there better ways to implement that but it wouldn't be an AR if he took different approach or 'fixed' his original design.
problem with stoner's design was that he didn't envision soldiers bashing enemy's heads with butt stock of his rifle. bayonet charge and hand-to-hand combat became obsolete with invention of machine-guns

ArmaLite actually did fix it, with their stamped steel AR-18 and moved springs to a better sturdier location. but that's a different story
 
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Would a piston upper fix the problem?

if you reduce stress on the rear of the receiver... it sure wouldn't HURT! however i think a better design would be like one on the M&P 15/22 where it's a solid piece of polymer with the stock attached to that. you of course will run into issues with the bolt hitting that though if i am not mistaken. i don't own one of these rifles so i can't just go look at one, just going on what i remember from ripping loki's apart.

the key here is to reduce stress on the weakest parts of the receiver. easier said than done, but you can get a reliable model going if you can do that. then again if all you really need is one shot--this works just fine the way it is. modern day liberator pistol!
 
there are ways you can get away by using printed plastic and still have a gun that sorta looks like an ar15 and takes same parts.
but that would take re-thinking/re-engineering entire area of the lower receiver where buffer tube being mounted.
easiest way would be probably using steel insert for where buffer tube screws-in and have enough plastic supporting insert so it doesn't just pop-out after one magazine of shooting.
 
there are ways you can get away by using printed plastic and still have a gun that sorta looks like an ar15 and takes same parts.
but that would take re-thinking/re-engineering entire area of the lower receiver where buffer tube being mounted.
easiest way would be probably using steel insert for where buffer tube screws-in and have enough plastic supporting insert so it doesn't just pop-out after one magazine of shooting.

True, a redesign of the "print" could solve the issue. I would just alter the design to include a monolithic thumbhole type stock that is not a separate part, but rather all one piece with the receiver, that way the obvious stress point where the buffer attaches would have better distribution of the forces. It still would likely shatter if you dropped the gun on the pavement because it is made of resin, but at least it should stay together while firing it.
 
yeah, printing gun parts technology is just not there yet and never will be as long as they use same filament as they do now.
however if engineers come up with some other material for filament that can offer much greater structural integrity, then the day it comes BATFE might want to make those printers or filament material a regulated item.
 
http://www.pagunblog.com/2012/02/15/how-to-cnc-an-ar-15-lower-from-delrin/

of course a more viable option, but not 3D printed. if you can CNC delrin, you can CNC aluminum.

eliminating the stress point is key, otherwise you'll be SOL. it's not so much that these are bound together, well, with something like a stratasys machine it all is melted together. depending on the thickness of the part would be whether it could handle a drop. when it's filled with and attached to metal though--i wouldn't bet on it surviving.
 
They have a machine that will do this but its millions for it. We have a prototype part made by the machine about the size of a soccer ball, this part cost us $20K made out of high temp steel. Not very cost effective....Yet!
 
...eliminating the stress point is key, otherwise you'll be SOL. it's not so much that these are bound together, well, with something like a stratasys machine it all is melted together. depending on the thickness of the part would be whether it could handle a drop. when it's filled with and attached to metal though--i wouldn't bet on it surviving.

When we wanted an FDM part to stand up a little better to abuse, we would brush on some methelyne chloride (I think?) to further fuse the first few surface layers. You couldn't dunk parts in to the solvent or the layers near the surface would bubble up like crazy.
 
If they knew anything about physics, mechanics, and metallurgy they wouldn't have bothered. Even with 3D printed "metal", it's basically sintered. No thanks!
 
If they knew anything about physics, mechanics, and metallurgy they wouldn't have bothered. Even with 3D printed "metal", it's basically sintered. No thanks!


I wonder if adding fibers (glass, carbon nano-tube) mixed into to the plastic filament would make a stronger material. My guess is yes.
 
I wonder if adding fibers (glass, carbon nano-tube) mixed into to the plastic filament would make a stronger material. My guess is yes.

Your guess is correct, but how do you implement fibers to create that matrix? You would need to build the 3D product on 2 planes instead of one and at that point you have 2 perpendicular directions of your fiber matrix where 3 directions I think would be the minimum.
 
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