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Usmc To Buy Polymer-Cased Ammo


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Trying to figure out which polymer they're using sent me down an hours-long rabbit-hole.

 

Judging from MAC LLC's patents, looks like it might be a 15/85 blend of PPSU (Radel) and plain old polycarbonate.

 

Strength, stiffness, thermal insensitivity and ductility are all important, but it's surprising a polymer that weak is suitable (about 9000 psi tensile strength).

 

I suppose all it has to do is seal the chamber seams during firing and then survive extraction, and there's a metal base to help with extraction, with the polymer case nested deeply into it, with gripping thread.

Edited by TTK Ciar
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All that really matters is the case head doesn't split, and the body obdurates the chamber. As long as the shooter doesn't get a facefull of gas, and the bolt face doesn't get gas cut, the case has done its job. I'd be more concerned about the thermal properties, is it more likely to cookoff? is it an effective heat sink to remove heat from the chamber, or a good insulator to keep the heat out of the chamber in the first place.

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From my lack of deep understanding on the matter, as the program is for 12.7x99mm, .50 cal ammunition, there is a big potential to reduce weight because it is a large round, and less possibilities of cook offs when firing from an open-bolt machine gun. Also, there is about an inch of brass in the cartridge head. It is remarkable that the ejected cartridges are not so hot, according to the video. Seems the polymer avoid heat transmission to the chamber.

 

Perhaps they used PC for strength, and the PPSU is intended to provide temperature resistance.

 

Probably aluminium is a better solution for 20mm, and up, calibers.

Edited by sunday
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CCI has made aluminum cased handgun ammo (CCI Blazer) for about 30 yrs. Didn't seem to be full powered, and Winchester White Box or Remington UMC wasn't much more expensive and reloadable as well. Big difference between loading a handgun case to 20k psi, and a rifle cartridge to 50k psi +. I don't know of anyone loading AL to .223 pressures, much less 5.56 lvl.

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So stop tossing them into the environment.

 

Denying our civilization the use of some of the most useful materials in history is not the right solution.

 

Keeping waste plastic out of the ocean shouldn't be that high a bar to reach.

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And it's not us doing it, in the main. Some statistics suggested that Chinese rivers were dumping in tonnes what ours were in kilogrammes.

India, too. For less-developed regions, the use of large rivers for garbage disposal is a given. For the locals, there are more important things.

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