3D printed upper.

Tinman45

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This has some interesting potentials, I would think. Someone smarter than myself might make a workable .22 upper, for example.

 

A&S Conversions

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They have made plastic AR-15s for years. I have never seen a polymer AR-15/M16 at a machinegun shoot. Could one be used, certainly. But it doesn't take many rounds to get the barrel hot enough to melt plastic. That is the "rub", at least IMHO.

Scott
 

Deerhurst

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Rimfire? Not an issue. Any other caliber, not really an issue as long as you can lock it all closed until chamber pressures drop.

Gotta keep heat off the plastic though.
 

A&S Conversions

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Rimfire? Not an issue. Any other caliber, not really an issue as long as you can lock it all closed until chamber pressures drop.

Gotta keep heat off the plastic though.

I am not sure I follow what you are saying. To me, metal parts would be used to contain the cartridge. The least expensive of such parts would be off the shelf. But those parts heat up from the combustion of the powder and the friction of the bullet. Those parts could be aligned to another firearm platform using 3D printed plastic material. What I have found with a machinegun mechanism there is a lot of heat very quickly. Could you dump several mags? Sure and there is lag time transferring heat to the outside of the metal parts to effect the 3D printed plastic parts.

It is my understanding that the home plastic printing materials have a melting point of around 350 degrees. But those materials get soft and can lose their shape well below the melting temperature. So you dump several mags and set aside the "upper". That lag time gets the 3D printed plastic soft and the "upper" deforms. That deformation could be enough to inhibit proper function when the parts have cooled and the "upper" is put on the machinegun again. If it is your design and printer or something that you have the programing for, just print another one. The printing material is cheap enough. But that gets much more complicated if you don't own those things.

With the Tenko adapter, I put somewhere around 5,200 to 5,300 rounds through the 3D printed version. I had five uppers and I would run a Beta-C or Surefire 100 round mag or four 30 round mags and then immediately change the upper. The heat had to go from the barrel to the AR upper, then from the front lug of the upper to the steel front pin of the adapter, then through the steel pin to the 3D printed adapter. I made it a point to always remove the upper from the Tenko adapter as soon as I finished firing the ammo through the upper to limit the transfer of heat from the hot upper.

I used one of PSA FN double chrome barreled uppers to check how hot the front lug would get with back to back Beta-C mag dumps. The front hand guard cap got so hot that the cheap plastic hand guards PSA had shipped on the upper melted into the hand guard cap. The front sight base was 700 degrees.

Could an upper receiver be printed for a Mac style RR, especially in .22lr caliber, I would think so. But I think that full auto fire would need to be very limited. I think that for a machinegun application, metal would be a much better heat resistant material, at least for those who don't own a 3D printer.

Scott
 

mak91

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I went though a number of 3d printed uppers when building my m11/22 prototype. At the time I was using petg filament. My upper mounts the feed ramp on the left side of the receiver. It acts as a feed ramp and also keeps the chamber of the barrel aligned dead center of the receiver. It slips tightly onto the barrel at the chamber. The area where the feed ramp bolted to the receiver distorted over time due to the heat but the thing that failed every time was the area around the take down pin. Every receiver cracked there after a few hundred rounds. There are things you can do in the design of 3d models to strengthen it up if the application allows. In the case of the area surrounding the pin that was cracking there was not much that could be done.
 

Deerhurst

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Petg tends to be pretty soft but decent thermal properties. I've also had good luck with some of the new resins.

Low temp printable thermoplastics can have the temps in which they distort as low as 120F for cheap stuff. With any material it is a balance of the properties.


As long as you can keep heat out of the plastic you are fine. As long as you can keep the chamber forces out of the plastic you are fine. This is why we can do AR uppers and similar so well with home 3D printing. The barrel and bolt so not need receiver to hold the pressures so the receiver can be very weak and not fail. Even AR aluminum uppers are very weak in many ways that a printed one may actually be stronger. Same for aluminum and plastic ar lowers. They both fail at the same spot when they fail. Same design, same weakness.


Rimfire doesn't create heat nearly like a center fire cartridge which is nice for using low temp materials.
 

Gaujo

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In the mac 3d printing subsection, nobody is printing uppers, just lowers, because a regular metal mac upper contains all the important bits that get hot, slam around, and contain explosions.
 

Deerhurst

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In the mac 3d printing subsection, nobody is printing uppers, just lowers, because a regular metal mac upper contains all the important bits that get hot, slam around, and contain explosions.
Barrel should be containing the explosion (not actually an explosion unless you run black powder) out you get a OOB detonation.


Mac uppers are cheap and not the firearm part. Same reason why people don't print AR uppers much. Not worth it when that is not the regulated part and can easily purchased and shipped to your door.


There are successful printed AK receivers that show you don't need all of it to be neutral, just the bits that hold pressure, barrel, bolt, trunnion. Keep it fairly cool and no issues until it physically wears out.

Also, thin printed things tend to be flexy. Welded sheet steel, not as much.
 

ecestu

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Same reason why people don't print AR uppers much. Not worth it when that is not the regulated part and can easily purchased and shipped to your door.
AR uppers are printed all the time. Look at companies like Hoffman Tactical. He's pumping out files for 3d printed uppers that uses less and less metal parts. He's getting pretty close to creating a metal-less AR-15.
 

Deerhurst

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AR uppers are printed all the time. Look at companies like Hoffman Tactical. He's pumping out files for 3d printed uppers that uses less and less metal parts. He's getting pretty close to creating a metal-less AR-15.
People have been doing mostly plastic ARs for decades.

The point I was trying to make is a significantly lower number of printed uppers exist when compared to printed lowers because there is not much point when the upper is not the regulated.

Use a roller cam if you want to run 556 in a plastic upper. Often the standard can will eat an aluminum upper.
 

Gaujo

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Some people get tatoos with ground up tires or pen ink, it doesn't happen much though. I've yet to see anyone 3d print a glock upper either, but that doesn't mean you can't. Back to the topic at hand, there is a gulf between the majority of the 3d gun printing community and people who really understand firearms and firearm design. They make guns with allthread running through them because their print bed isn't big enough for a single piece design, fundamentally weakening the whole thing. There are two groups. People trying to use 3d printers to see what kind of gun they can 3d print, and people trying to use the abilities of a 3d printer to make better guns, prototype new guns, or include features that aren't available on a retail gun.

I realized this after making a poison sumac. A ultra cool looking gun, but a weak firearm design. I personally wouldn't mess with a mac design that had a printed upper as there is it would only be substituting inexpensive and well working metal parts for much weaker plastic ones.

For example the lower I'm working on now I am pursuing because it's one piece, uses glock mags, and has an ar-15 trigger group. You can't get that anywhere.
 
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