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Polymer AR-15 lower


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Old 05-19-2012, 11:39 AM   #21
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Apparently H&K is satisfied with the strength of polymers. Example the XM8 platform.

I fully expect that the majority of new small arms development will rely very heavily upon polymer construction moving forward.
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Old 05-19-2012, 11:56 AM   #22
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Apparently H&K is satisfied with the strength of polymers. Example the XM8 platform.

I fully expect that the majority of new small arms development will rely very heavily upon polymer construction moving forward.
"which would start to melt after firing too many rounds." Not too sure about H&k
I don't like some of the issues the internet has shown in regards to polymer in high stress areas.
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Old 05-19-2012, 04:46 PM   #23
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Apparently H&K is satisfied with the strength of polymers. Example the XM8 platform.

I fully expect that the majority of new small arms development will rely very heavily upon polymer construction moving forward.
That rifle was designed from the ground up to be made of polymer, and that makes all the difference. You CANNOT (in most cases) simply make the same part in the same form factor using polymer and expect it to perform the same or better. Unless the part was made from inferior materials to begin with. I.E. too heavy/strong or too weak for the intended job. When someone redesigns the AR-15 lower with the intent to build it from polymers, it might be worth a look. Until then, I'll pass.

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Old 05-19-2012, 04:48 PM   #24
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Apparently H&K is satisfied with the strength of polymers. Example the XM8 platform.

I fully expect that the majority of new small arms development will rely very heavily upon polymer construction moving forward.
No doubt this is true but those arms will be initially designed for polymer like the Glock was. So far it's been difficult to reverse engineer polymer receivers for the AR. Not saying it can't be done but I'm sticking with 7075 T6 for now.
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Old 05-19-2012, 09:29 PM   #25
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Every time this subject comes up, I spend a lot of time thinking about why it can't be done like they are trying it now. So Today I spent some time thinking about how it can be done. From what I have seen on the internet about polymer lowers failure mode, they seem to fail at the area between the rear take down pin and the buffer tube attatchment. To me this says that that area stresses enough to fatigue the polymer and cause a failure. So as I see it, the way to make this idea work, one would need to strengthen that area and stop the flexing. The best way to do that as I see it would be to incorperate the entire buffer tube in the lower. This could be done by incorperating something like the magpul UBR stock design into the lower. Add to that beefing up the backstrap area where it curves from the grip up to the buffer tube. Like incorperating what many of the aftermarket grips add to that area. The sidewalls of the lower in the FCG area would need to be thickened outward as well. All of these changes would obviously make the lower less customizable and maybe even cost prohibitive. But thats how I would skin that cat.

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ETA the charging handel is the primary resrtiction to doing it other ways. Change the upper to side charging and a whole world of opportunities opens up.
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Old 05-19-2012, 10:51 PM   #26
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Originally Posted by EW1066 View Post
Every time this subject comes up, I spend a lot of time thinking about why it can't be done like they are trying it now. So Today I spent some time thinking about how it can be done. From what I have seen on the internet about polymer lowers failure mode, they seem to fail at the area between the rear take down pin and the buffer tube attatchment. To me this says that that area stresses enough to fatigue the polymer and cause a failure. So as I see it, the way to make this idea work, one would need to strengthen that area and stop the flexing. The best way to do that as I see it would be to incorperate the entire buffer tube in the lower. This could be done by incorperating something like the magpul UBR stock design into the lower. Add to that beefing up the backstrap area where it curves from the grip up to the buffer tube. Like incorperating what many of the aftermarket grips add to that area. The sidewalls of the lower in the FCG area would need to be thickened outward as well. All of these changes would obviously make the lower less customizable and maybe even cost prohibitive. But thats how I would skin that cat.

EDUB

ETA the charging handel is the primary resrtiction to doing it other ways. Change the upper to side charging and a whole world of opportunities opens up.
Sounds like magpul needs a poly lower , that stuff is very strong, very durable and would prob be better than the rest of them out all
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Old 05-20-2012, 01:58 AM   #27
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^ its been done... search Calvery Arms Lower
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Old 05-20-2012, 02:20 AM   #28
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Originally Posted by EW1066 View Post
That rifle was designed from the ground up to be made of polymer, and that makes all the difference. You CANNOT (in most cases) simply make the same part in the same form factor using polymer and expect it to perform the same or better. Unless the part was made from inferior materials to begin with. I.E. too heavy/strong or too weak for the intended job. When someone redesigns the AR-15 lower with the intent to build it from polymers, it might be worth a look. Until then, I'll pass.
EDUB
That sounds like the best advice yet.
Problems with pins getting loose? Build a sheet metal cage like the H&K G3 /91 uses.
Weakness in the take-down pins? Redesign the interface, perhaps even completely do away with the front pin so that when the rear pin is punched out the front just levers away.
Lack of strength in the receiver extension? Design a completely different one, if it's strong enough mfg's will make parts for it. No one offered accessories for Glock when they first came out, did they?

Don't expect a copy of an aluminum receiver built from polymer to perform as well as a receiver purposely designed to be build from polymer. Accept that there will be certain things that can't be switched from one to the other.
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Old 05-20-2012, 02:59 AM   #29
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I just bought one and i got some mags for it and well let's jus say it's pretty tight the only one that fits right is the one that came with it
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Old 05-20-2012, 10:22 AM   #30
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There is the rub. When you reinforce the weak areas in a polymer design you end up with the same weight or more than you had with an all aluminum build.
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