Polymer AR-15 lower receivers

[shootstraight57]

Do they really hold up under normal conditions?
I am in the middle of my build and came across a polymer lower. The AR will be of carbine length and used for plinking and home defense.
My question is has anybody have any experience with polymer lowers and were they negative or positive.
Forgive me if I posted this in the wrong section.

 

[dogmush]

Define normal use.

I have two poly lower AR 15's. (both built from 80% lowers) They shoot at the range just fine. I have about 3000 rds through the 5.56 one and maybe 1000 through the .300blk. Accurate and reliable (not that those are functions of the lower in an AR) I would not hesitate to grab the .300 to go on a hunt, or for that matter the 5.56 if something goes bump in the night. I also don't baby my guns. I'm not dragging them behind my truck, but they've been dropped, thrown in a soft case and thrown in the truck, dropped on a sling to bounce around, stuff like that.

If I was going to a Combat zone I think I'd rather have an Aluminum.

For most of us here, yeah I'd say (mine at least) are holding up to "normal use".

My question to you would be why? I did it specifically because a poly 80% lower is easier to machine and finish then an Aluminium one. If you are going for a super light weight build you can save a few ozs. (But only a few. You'd be surprised) Other then that, why bother?

 

[USAF_Vet]

I've got one of the ATI omni polymer lowers mated to a DPMS upper. I've put it through more than just range time. Its held up pretty well, but I do want to replace it with aluminum and maybe use the poly for another project, like a 9mm or .22lr.

I got this one in October of 2012, just before Newtown. None of the pins have walked, hammer is kinda junky but it hasn't failed to ignite primers.

For a range rifle, they hold up just fine. I've seen failures, just never in person. With the cost of ARs being so low, I wouldn't choose a new build from a poly lower unless I just had one laying around.

 

[dogmush]

I've got one of the ATI omni polymer lowers mated to a DPMS upper. I've put it through more than just range time. Its held up pretty well, but I do want to replace it with aluminum and maybe use the poly for another project, like a 9mm or .22lr.

That's funny, I specifically didn't use a poly lower on my 9mm because I've heard they are rougher on the hammer pin and didn't want to egg that hole.


ETA: FWIW, I like mine enough that when JMT offered a poly AR10 lower at pre-sale prices I picked one up.

 

[briansmithwins]

I don't have a problem with poly, as long as the item in question was designed for it. SCAR, ARX, AUG, or Tavor are all fine by me.

But polymer and forged aluminum have very different mechanical properties, and I'd be very hesitant about just substituting one for the other in any application where there is stress.

Besides, 7075 aluminum lowers are running from $40 on up, so the cost savings can't be that much.

BSW

 

[Ed Ames]

... polymer and forged aluminum have very different mechanical properties, and I'd be very hesitant about just substituting one for the other in any application where there is stress.

This is a good example of a plastic lower "done right":



Notice that they didn't follow the standard design for the buffer tube/stock-to-receiver transition. From what I read that was part of the reengineering they thought was required to avoid cracking at the buffer tube mount ring. Basically they didn't trust plastic there and instead permanently attached a fixed stock, giving them a much stronger finished product.

The stated goal was to be able to sell entire assembled lowers for $100 or so. The ATF shut them down but another company bought the tooling and still makes them (though not at a reasonable price from what I've seen).

That, plus a standard 16" carbine upper, will give you a 6lb AR without even trying. Swap a few lighter parts onto the upper and you can shave another half pound without heroics, or more if you want.

 

[Jackal]

Stand alone poly lowers are not suited to any serious use. They break. Simple as that.

 

[dogmush]

Stand alone poly lowers are not suited to any serious use. They break. Simple as that.

I love broad brush absolute statements. They so further the discussion.

What do you consider "Serious use"?

I shoot more 5.56 then a lot of folks I know, I have a poly lower that is doing EXACTLY what the OP is asking about, not only is it not broken, it doesn't actually show any noticeable wear. I even gave an approx round count for him to think about.

So when will my lower break? At what round count? Or should I go ahead and fix a bayonet to beat it into submission?

 

[BSA1]

I likewise looked at polymer receivers for my first build and could not find any advantages in it.

Aluminum is more durable, stronger and gives the owner a wide variety of finishes...anything from Ceracoat to Hard Chrome and colors from Pink to Camouflage at the same price as polymer.

 

[Jackal]

So when will my lower break?

When you drop it, trip, fall down, falls off tailgate, etc. Actual field situations. Serious use. Accidents happen and polymer lowers break. Poly lowers snap at the buffer tube and poly uppers let go at the barrel extension. I'm not making it up, there are hundreds of threads online showing these exact situations.

 

[cfullgraf]

I've had one polymer lower and have broken one polymer lower.

Data point of one but good enough for me to steer clear of them.

 

[Sunray]

Glocks et al are polymers. Stand up just fine to neglect by cops and others. No reason to think a polymer AR would be any different.

 

[SuperNaut]

I'm seeing sub $50 aluminum lowers all over the place. Makes it tough to justify paying more for polymer.

 

[Olympus]

My question is why buy a poly lower when you can get a forged aluminum Anderson for like $35 at AIM?

 

[Inebriated]

Glocks et al are polymers. Stand up just fine to neglect by cops and others. No reason to think a polymer AR would be any different.

Hardly comparable.

 

[Jackal]

Glocks et al are polymers. Stand up just fine to neglect by cops and others.

As previously stated in this thread, guns that are DESIGNED to be made of polymer generally work great. AR's however were not designed to use polymer receivers and as such, there are severe weak points at the stressed areas. Some companies have addressed this with bulked up stress points or metal reinforcement. But honestly, when a forged lower runs $40 and a billet can be had for $120, why even bother?

 

[chicharrones]

Do they really hold up under normal conditions?
I am in the middle of my build and came across a polymer lower. The AR will be of carbine length and used for plinking and home defense.
My question is has anybody have any experience with polymer lowers and were they negative or positive.
Forgive me if I posted this in the wrong section.

Home defense? No way I'd use a polymer lower in an AR that would be relied upon for home defense.

As I understand it, when the AR is fired the buffer bottoms out at the end of the receiver extension. The receiver extension mount on the lower is taking all the load when the buffer bottoms. Since the receiver extension is only attached at the lower, and has no upper support, the receiver extension tries to flex downward in recoil. Sure, the buffer and buffer spring soften the blow when bottoming, otherwise an aluminum AR lower might not last a long time either*.

https://youtu.be/WSqYvWib1og

In my view, it's like standing on a cantilevered wall shelf or standing on a ladder rung. The shelf only has support on one side, the ladder rung has support on two sides.

I've seen that pistol ARs with poly lowers break faster than rifle ARs with poly lowers. Why? Probably because the rifles are shouldered and the shoulder helps take the load when the buffer bottoms out. Pistols fired free hand have no extra support.

*Compare to a worn and battered break open shotgun here. http://www.americanrifleman.org/articles/2015/3/4/are-your-guns-tired-and-stressed/

 

[chicharrones]

This is a good example of a plastic lower "done right":

The one piece Cav Arms lower is one I would be willing to try. http://www.gwacsarmory.com/

 

[Walkalong]

I'm seeing sub $50 aluminum lowers all over the place. Makes it tough to justify paying more for polymer.

This right here.

 

[Ed Ames]

... But honestly, when a forged lower runs $40 and a billet can be had for $120, why even bother?

Weight.

I have a forged lower with a fixed ultralight stock that is literally an aluminum buffer tube with a foot on one end. It was built to be light, including weighing receivers in the store to find the lightest, and a ready-to-run Cav-15 beats it by half a pound.

Maybe to remove temptation.

If my small amount of googling a few minutes ago is correct, I can get a stripped cav-15 for $90. Add carbine buffer/spring and a parts kit for $55ish and you are done at $145.00. In contrast, to get exactly the same fixed stock configuration with a $40 forged lower will need the same $35 parts kit, a $63 stock/buffer, and another $5 for a pistol grip for a total price of $143.00 . . . but . . . going this route I can just as easily spend $20 on the grip and $150 on the stock for a total price of $245.

 

[dogmush]

When you drop it, trip, fall down, falls off tailgate, etc. Actual field situations. Serious use. Accidents happen and polymer lowers break.

Except that I have dropped, and it's fallen off things (Hood of my truck, little half wall at the range). I've used one in actual field situations, and it works, and doesn't break.

Which is not to say I couldn't break it. Hell I've seen people break Aluminium M16 lowers. Sure it'll break eventually. Possibly before an AL one. Dunno, Poly lowers these days are beefed up and thicker in the failure areas, so without testing them to failure it's hard to guess.

Also, sure I can find stories of Plum Crazy lowers breaking, as well as the Carbon 15 ones. I can also find stories of early M16's being unreliable. Designs got tweaked, and lots of those issues got fixed. Build what you want. I have metal and poly guns both. It just irks me when I see "It WILL break" with little data and no discussion of which design might be better or worse. [shrug] I'll let you guys know if mine breaks, then we'll have data.

As to the why: Weight, or ease of machining, like I said in my first response. I think most Poly lowers are actually MORE expensive then Al ones these days, what with the glut of AR parts. So unless you want the features that Poly can give you, it's probably not worth the cost. But those features are there.

Either way the OP can build whatever. That's what makes America great. I'm going to a buddies house to run a couple thousand rounds down range, and a bunch of them will be through my Poly AR-15 pistol. We'll do some running and shooting before Fireworks. (Fire works will include some Star Clusters from my RV85) It DEFINITELY will not break.

Happy Fourth.

 

[kwg020]

I have 4 polymer lowers from this company. I put a light weight upper from Del Ton on one. It's now my son's everyday shooter. The other 3 are in transition to various calibers and barrels. I have confidence they will be around long after I am finished with them.

http://tnarmsco.com/

 

[Dr.Rob]

I ran one (New Frontier) pretty hard at a tactical rifle match mated to my Colt upper. Worked just fine though the trigger is lousy for long range shooting. I got it for a hundred bucks assembled and complete with stock, buffer tube etc. It's mated to a dedicated 22 upper now, and I think I got my $100 worth out of it.

I have a couple other AR's for 'serious' work.

 

[Skyshot]

I've got a Plum Crazy lower on a dpms oracle upper. Use it for range plinking and coyotes. I've had it for several years and its run several K rounds through it. It hasn't broke yet, but I don't treat rough either. I realize its structural weak points and don't push them. It's a nice lightweight carbine and when it does breack ill swap it out with something else.

 

[shootstraight57]

Thanks for all the information and personal comments. I was looking for some true life experiences with the polymer lowers and you guys have had a gambit of ups and downs with them.
Thanks for the info.
Well after reading all the comments I went out and bought a aluminum lower receiver. I was trying to build a light weight carbine but didn't want to sacrifice on strength.
With all the pros and cons of polymer and aluminum lowers I made the choice.
Thanks THR community.