Polymer Lowers, Good Or Bad?

This subject has been argued and rehashed many times on here and the general feeling is always that they are only good for a lightweight range plinker, and/or a dedicated .22 build. I have to think that S&W did their homework and would never have risked using poly if it was the least bit risky when they designed their 15-22. There are millions of those out there and you really don't ever read of those breaking. I personally own one and feel it's perfectly suited for what these rifles are used for. For a battle rifle, not so much...
 
I agree. I love the weight of the 15-22 for new shooters. I would prefer it to be a little heavier for myself. Of course I would like to not have a pinned stock either.


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They are no longer shipping lowers to Massachusetts as evidenced by the second round of the group buy

I got my poly from Palmetto State last February. They shipped it to me without issues. They called me and asked me for my FFL information gave it to them and it was shipped.

I personally think some of these (in general) breaks are from over torquing (not the proper torque) the buffer tube.

If they are GenII that should tell you something ;)
 
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I am in NH. I bought some metal lowers last time and plan on buying the group buy Blems. I was just curious about how polymer lowers hold up because I saw one in the store and have not personally dealt with them yet. I will (hopefully) never have to live in Massachusetts.
 
Any reason why they stopped shipping to MA? I would think that a lower wouldn't have any problems, even with the AWB.

I know it seems to fly in the face of common sense but MANY online vendors refuse to ship ANYTHING firearm related to MA at all, let alone something such as a lower that can be made into a baby killing black stick of doom. PSA will still sell accessories and even uppers to inmates of MA, just no lowers or ammo.
 
Hmmm. Interesting. I can't figure out why they didn't make some sort of adjustable stock mount instead. This is 2022. I have mixed feelings about hte permanent pistol grip as well. I like having the option to remove one, but do I ever WANT to remove it?? No. Not really.
 
My nephew got to take it out with a .22lr upper on it and he loved it.
i totally get the idea of using it with a 22lr upper, but it escapes me why anyone would put that on a proper .223 or, AR10 build. i hope ar10 plastic shit does not even exist, it better not.
i would also think the trigger pins will not stay on those holes for very long, it has to develop play as holes will eventually be pushed out of shape.
and also do not get it - for how long will be handle buffer tube stress - if used in a proper .223? looks like a total BS to me, to be honest.
 
Hmmm. Interesting. I can't figure out why they didn't make some sort of adjustable stock mount instead. This is 2022. I have mixed feelings about hte permanent pistol grip as well. I like having the option to remove one, but do I ever WANT to remove it?? No. Not really.

I have a couple of AR's that had Magpul furniture on them. I picked up a DDM4A1 and liked the furniture so much that I replaced the Magpul stuff on my other ARs with the DD parts.
 
i totally get the idea of using it with a 22lr upper, but it escapes me why anyone would put that on a proper .223 or, AR10 build. i hope ar10 plastic shit does not even exist, it better not.
i would also think the trigger pins will not stay on those holes for very long, it has to develop play as holes will eventually be pushed out of shape.
and also do not get it - for how long will be handle buffer tube stress - if used in a proper .223? looks like a total BS to me, to be honest.
Polymer frame handguns don’t have an issue with trigger pins walking out. And there are a number of military carbines with polymer lowers. KE Arms claims mil-spec fire control groups will work just fine. But if you use a cassette-type drop-in trigger, they recommend one with it’s own retention clips. The receiver is slightly thicker at one of the trigger pins and therefore standard anti-rotation pins/pins with screws on the ends won’t work.

And the buffer tube/stock is heavily reinforced, it’s a sturdy receiver. This receiver’s durability isn’t a con.

There is no KP-10 receiver for 308 and they don’t intend to make one because of the costs to make good molds. There are polymer AR-308 lowers, but they try to be the same shape as aluminum lowers and therefore are crap.

KE Arms does have a KP-9 though that takes Glock mags. But it is only designed for direct blowback 9mm uppers and last round bolt hold open is dependent on the upper. The lower has nothing to enable it with the Glock mags. CMMG radial delayed uppers would require modification to the ejector in the lower.
 
Hmmm. Interesting. I can't figure out why they didn't make some sort of adjustable stock mount instead. This is 2022. I have mixed feelings about hte permanent pistol grip as well. I like having the option to remove one, but do I ever WANT to remove it?? No. Not really.
It was all done strictly for durability and to prevent weak points in the receiver. I think it was a smart decision. Other rifles with polymer lowers don’t have to worry about a section coming up in-line and behind the action and potentially creating a narrow section of polymer.

But the fixed stock and grip are definitely cons to the receiver.
 
KE Arms claims mil-spec fire control groups will work just fine
an interesting statement, i cannot truly see how it can be true, but, ok.
in none of polymer pistols you'd have a bolt smacking like that straight at the hummer that itself sits on a rather stiff spring and all that sits on a pin that get stressed down into the frame through this process. just from mechanical engineering standpoint it has to develop a play in the plastic, eventually. perhaps that 'eventually' is quite a big number, then, according to the KE. dunno.
but, good to know, anyway.
 
i've done a polymer 80 lower...maybe 10 years ago. they beefed up the rear of the lower to combat the cracking that happened at the threads for buffer tube installation. i've shown mine before and will add a pic below. one detail they didn't mention is since there is more lateral meat in the vicinity aft where the take down pin is, your pin that comes with the lower kit will not sit flush with the frame. it still works fine and is all esthetics but i then found out after it was put together polymer 80 sold a longer pin on their website to fix the situation. i've circled the misfit pin size in my photo. but i've got many thousands of rounds through this lower without signs of stress. it's not my main rifle so it's not one of the ones i'd grab first to go off and shoot. it's usually an after thought. and i built it on the skinflint cheap to see if i could. the upper is a $225 bravo co. blem 2nd. i think the larue rear sight was maybe half the build cost. but the handguard was a freebie. it turned out very nicely and is surprisingly accurate. runs like a champ on 55gr 5.56's which is good cause i got a ton of 'em. inside the red circle you can see the pin doesn't come thru fully.

80%25B.jpg
 

in none of polymer pistols you'd have a bolt smacking like that straight at the hummer that itself sits on a rather stiff spring and all that sits on a pin that get stressed down into the frame through this process. …

No, but you do have such things in the various polymer receiver service rifles around the world.
 
Hmmm. Interesting. I can't figure out why they didn't make some sort of adjustable stock mount instead. This is 2022. I have mixed feelings about hte permanent pistol grip as well. I like having the option to remove one, but do I ever WANT to remove it?? No. Not really.
Strength.

The rear of the lower if it was built to the standard AR dimensions would fail. Apparently lots of Cavalry Arms lowers failed in that location. The KE Arms lower is significantly beefed up in that location (and in other locations like at the pin holes).

Plastic molds are expensive. Really, really expensive. A collapsible stock would cost more to design and manufacture while being weaker than a fixed stock.

And KE has been defending itself from what appears to be a frivolous lawsuit from GWACS Armory over this design for the past couple years.
 
Forged vs billet polymer. The latter is stronger...
??

billet polymer?

I'm not sure what you're trying to say here.

We don't "forge" plastic, we injection mold it. We don't tend to talk about machined plastic as "billet" since that's mostly a term that's been glommed onto by the commercial firearms industry for marketing purposes. A billet is just a chunk of material.

When talking about aluminum lowers, forged parts are generally stronger than "billet" (often, extruded) parts. The commercial preference comes from the fact that the CNC process makes it easier to quickly produce new, complex designs - allowing them to add flared mag wells and custom trigger guards without expensive investments in custom tooling. That extra machine time is costly though, so they pass that on to the customer via premium marketing.
 
Polymer lowers if done right are fine. Even though a little different than AR15, FN Scars have polymer lowers and not an issue. Sure they can break but they can take a lot, a lot of abuse.

I don't disagree, but would toss out there that the SCAR lower has no buffer tube. That's a critical point of failure in a polymer AR lower. With a scar, the upper just sits on top of the lower with no parts of the lower protruding into the upper space going perpendicular to the direction of the action. So the stress points are mainly the front pin hole and the rear tab section that slots into the stock. I'm assuming it would be easier to reinforce those sections over a buffer tube housing.
 
I don't disagree, but would toss out there that the SCAR lower has no buffer tube. That's a critical point of failure in a polymer AR lower. With a scar, the upper just sits on top of the lower with no parts of the lower protruding into the upper space going perpendicular to the direction of the action. So the stress points are mainly the front pin hole and the rear tab section that slots into the stock. I'm assuming it would be easier to reinforce those sections over a buffer tube housing.
Reportedly the KE Arms folks did a lot of design and testing in order to ensure durability of the buffer tube. This was addressed on one of the InRange videos, IIRC.
 
Reportedly the KE Arms folks did a lot of design and testing in order to ensure durability of the buffer tube. This was addressed on one of the InRange videos, IIRC.

I'm betting more modern polymer AR lowers are fine these days. Lots of the more recent models I've seen are either rather beefy from the selector to buffer tube span, or some even have metal reinforcement parts. I think that might be an issue of the past.
 
??

billet polymer?

I'm not sure what you're trying to say here.

We don't "forge" plastic, we injection mold it. We don't tend to talk about machined plastic as "billet" since that's mostly a term that's been glommed onto by the commercial firearms industry for marketing purposes. A billet is just a chunk of material.

When talking about aluminum lowers, forged parts are generally stronger than "billet" (often, extruded) parts. The commercial preference comes from the fact that the CNC process makes it easier to quickly produce new, complex designs - allowing them to add flared mag wells and custom trigger guards without expensive investments in custom tooling. That extra machine time is costly though, so they pass that on to the customer via premium marketing.

It was a joke. For some reason I couldn’t add an emoji to that effect, so I opted for three dots. Hopefully you can now enjoy my attempt at humor.
 
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