Polymer lower for PCC

[Kestryll]

I built a 9mm upper with the plan to swap it out with one of my regular lowers but I had a thought. I have an older polymer 80% lower kit I've never done anything with and i got to thinking maybe I should finish it out and use it for the 9mm upper.

I know all the arguments against polymer lowers for 5.56/.223 and frankly I'm not inclined to ever use it for a rifle caliber which is why it's still in the original wrapper.
However I'm wondering if the poly lower might be okay for a 9mm carbine. The recoil forces, pressures and such should be far lower than with a rifle caliber and while they're not exactly the same thing polymer pistols have become a proven tech by now.

So....

Any experience or thoughts on using the polymer receivers for 9mm uppers, good idea, bad idea, so crazy it just might work or just plain crazy?

[kevins750]

I am not going to say yes or no, but I had a poly lower on a X39 for about 300rds. I don't remember any ill effects.

[AlienHobo]

I use an ATI Omni Hybrid Polymer AR15 Lower on my 9mm PCC. I've got about 800 rounds through it and it's still working fine. Brought it to the last SSZS and had no issues.

I use the EndoMag 9mm insert and have not had any issues after the first 100 rounds.

[DrewTheBrave]

Short answer: I would only use a polymer lower for a .22 caliber AR.

The recoil of a 9mm may feel less than that of a 5.56, but the blowback system most pistol caliber carbines use means the carrier is a lot heavier than a standard carrier. I would worry about all that extra reciprocating mass slamming back and forth in the tube, as the receiver extension tube attachment point is typically where polymer lowers fail.

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[jeremyro]

As said above the shock to the lower is greater with 9mm than 5.56 because it is straight blowback. I would not do it.

[edgerly779]

I RUN A COUPLE NFA POLYMER AND HAVE HAD NO ISSUES.

[Oldmandan]

I’ve never had issues with any of my NFA lowers.

All the cracked lowers I’ve seen on the www are the Plum Crazy Lowers, never seen anything else crack...

[sigstroker]

I built a 9mm upper with the plan to swap it out with one of my regular lowers but I had a thought. I have an older polymer 80% lower kit I've never done anything with and i got to thinking maybe I should finish it out and use it for the 9mm upper.

I know all the arguments against polymer lowers for 5.56/.223 and frankly I'm not inclined to ever use it for a rifle caliber which is why it's still in the original wrapper.
However I'm wondering if the poly lower might be okay for a 9mm carbine. The recoil forces, pressures and such should be far lower than with a rifle caliber and while they're not exactly the same thing polymer pistols have become a proven tech by now.

So....

Any experience or thoughts on using the polymer receivers for 9mm uppers, good idea, bad idea, so crazy it just might work or just plain crazy?

They aren't. Bolt/carrier speeds are much higher in a 9mm than a 5.56. Usually heavier too. Then you have to dick around with a mag adapter too.

[69Mach1]

I built a 9mm upper with the plan to swap it out with one of my regular lowers but I had a thought. I have an older polymer 80% lower kit I've never done anything with and i got to thinking maybe I should finish it out and use it for the 9mm upper.

I know all the arguments against polymer lowers for 5.56/.223 and frankly I'm not inclined to ever use it for a rifle caliber which is why it's still in the original wrapper.
However I'm wondering if the poly lower might be okay for a 9mm carbine. The recoil forces, pressures and such should be far lower than with a rifle caliber and while they're not exactly the same thing polymer pistols have become a proven tech by now.

So....

Any experience or thoughts on using the polymer receivers for 9mm uppers, good idea, bad idea, so crazy it just might work or just plain crazy?

It depends on the lower. This is a first gen. Built as a dedicated 9mm. The replacement i received is "reinforced ", and I've put another 200 rounds in it so far.

[zhyla]

You can’t actually build a polymer lower in CA now though can you? Not legally I mean.

[plumbum]

80% rifle, yes
80% pistol, no

[edgerly779]

^^^ How do you add the 3.7 ounce stainless plate on polymer 80% rifle?

[zhyla]

^^^ How do you add the 3.7 ounce stainless plate on polymer 80% rifle?

[Sequencer60]

80% rifle, yes
80% pistol, no

So, THIS wouldn't be legal?

http://www.calguns.net/calgunforum/showthread.php?t=1633692&highlight=80%25

[ar15barrels]

So, THIS wouldn't be legal?

http://www.calguns.net/calgunforum/s...ighlight=80%25

That's not legal to assemble into a semi-auto firearm in CA.
He must be selling it to someone who is going to move it out of CA before they finish the reciever and assemble it.