View Full Version : Polymer AR Lowers - Again

August 15, 2012, 01:16 PM
Been wanting to do a 458 or 50 Beowulf build for a while now and have ran across some polymer lowers for inexpensive. I know you get what you pay for, but I also know a lot of price is driven by name association too. So this being said, has anybody had ANY experience with some of these polymer AR lowers?


I had read a guy did one of these on a Beowulf build and has held up for a while now too.

Anywho, thoughts? Opinions w/reasons?

August 15, 2012, 01:27 PM
there are some guys on here who do have the plum crazy lowers but alot of them run aluminum lowers.

August 15, 2012, 03:43 PM
Just finished building my lower. Spikes lower, Bushmaster LPK, Spikes m4 stock with buffer tube, st2 buffer, and spring and she weighs in at 2.2lbs. I probably could have done much better with a different stock but for the .6 lbs difference I will stick with 7075 t6. You can easily make up that weight difference in other areas before your done. Just my .02 worth ymmv.


August 15, 2012, 09:23 PM
So what happens if you have to mortar a polymer lower when it jams?

August 16, 2012, 07:01 AM
I had a spare upper and BCG laying around that I had been swapping with the upper on another build. I always figured I would get another lower and complete a second rifle some day.
When I saw the great price and great reviews on the New Frontier lower, I jumped.
I picked up the lower from my rifle clubs FFL and went directly to the range. Snapped on my upper and tried it out...it worked perfectly.
After 500 rounds through it, it still does...I'm pleased.

August 16, 2012, 08:29 AM
I have seen pics of buffer tube extensions breaking on the poly lowers, but knowing polymer, it would take a considerable amount of force-more so than an average man could exert-to break one.

August 16, 2012, 09:01 AM
On my 300 Blackout assembly I wanted to make everything as light as possible so I used a Plum Crazy lower. After around 2200 rounds it has worked flawlessly and the trigger is much smoother than the one that came with my last BCM assembly. Since I reload and have tested out numerous loads for the 300 Blackout from 110 grain to 245 grain bullets some OAL's were not workable and I've had to mortar the rifle 4-5 times without any problems so far.

August 16, 2012, 10:01 AM
I have seen pics of buffer tube extensions breaking on the poly lowers, but knowing polymer, it would take a considerable amount of force-more so than an average man could exert-to break one.

The pics I've seen of busted polymer lowers all broke in the same place- right at the rear takedown pin hole. Presumably, the hole through the lower for the takedown pin detent and spring left those particular lowers weak at that point.

However, from the pics I've seen of the New Frontier lowers, they reinforced that area, so it should be OK. My real concern with the NF lowers is with the plastic fire control group, but I've yet to see anybody complain about a problem with that, so my concern is probably overblown. I still don't know that I'd get one myself, but they seem to be just fine for most purposes.

August 16, 2012, 10:34 AM
I went in with an open mind on the polymer LPK, knowing I could replace it with a standard metal LPK if I didn't like it.
No plans to do that so far...it has a nice trigger pull with little over travel.

August 16, 2012, 10:52 AM
Danger, Danger: I'm trying to recall something, but can't find the reference:
Doesn't the Bushmaster upper info explicitly say to NOT use a poly lower?

I've read/heard/hallucinated this somewhere, but cannot find the source...Maybe ar15.com.
Take this with a grain of salt.

August 16, 2012, 10:53 AM
Since the lower IS the firearm, I'd pay a little more and put up with a few more ounces to get a quality 7075-T6 lower with a rollmark I like. An extra $50 is a drop in the bucket when you consider the cost of the entire rifle. I'd bet you'd lose more on resale, too, if it ever came to that.

August 16, 2012, 06:25 PM
From the people that have or know people that have these they seem like an okay to good deal. The only negative I've seen posted on a few forums are from people that don't have them.

Sounds like I may give this a go.

August 16, 2012, 10:54 PM
If you're looking to run a .50 Beowulf, get a mil-spec lower. Just one guy's recommendation. I know from experience that the Beowulf's recoil can be punishing on other components of the rifle. I had a Trijicon reflex sight that couldn't keep a zero because of the recoil. While optics and the lower receiver are different, the polymer lowers are designed to handle the .223/5.56 round. You may have to spend a bit more money, but buying mil-spec in this instance might be your best bet.

August 16, 2012, 11:01 PM
I have one of the New Frontier Armory polymers on a varmint rifle build and I have nothing but good things to say about them. Trigger pull was very good. So far, two shots fired, two groundhogs retired.

August 17, 2012, 03:31 AM
I'm curious are they making their own FCG? if not the trigger pull will be the same as anyone elses. Me personally it took me plenty long enough to go from steel to aluminum, I have zero intentions to go from aluminum to plastic, on any gun.

August 17, 2012, 10:12 AM
Despite how much I dislike FPS Russia, he is doing a torture test on an FA Poly lower, and I am curious to see how well it holds up.

August 18, 2012, 09:36 AM
My son and I were discussing polymer lowers last night.
I told him I couldn't figure out why they had not become much more popular.

Polymers have proven their durability in the compact carry market. Modern composites are extremely light, durable, and probably less expensive than mil-spec aluminum components.

Some composites can be pretty exotic, so I'm sure their costs would exceed aluminum. But I don't see why a lower would be subjected to those kinds of stresses.

The SCAR platform utilizes a polymer lower...so it's GOTTA be strong enough.

Why it has not caught on more extensively in the AR platform is beyond me.

August 18, 2012, 03:02 PM
Why it has not caught on more extensively in the AR platform is beyond me.

Because it needs to be well done in order to gain much of a following. Most polymer AR receivers have not been. Although this would seem to be changing, it isn't as simple as just changing the material of the lower- there's a few spots that need to be reinforced as well, and if they aren't, well, it's going to break and give polymer a bad name.

It now seems like some are doing them well, but keep in mind it took over a decade for polymer to become a popular choice for handguns, and even then it was generally not done as a replacement for steel or aluminum but as new designs entirely.

Polymer will begin to overtake forged aluminum for AR receivers when they are done well (seems like we're getting to this point finally) and they bring something to the table that the forged aluminum doesn't*, and it does this for an extended period of time.

* It will need to be either cheaper or lighter, and preferably both. Given that forged aluminum lowers can be had for $80 or so right now, I'm not sure just how much room there is to make an aluminum lower that much cheaper. Even at half the price you're still talking only a $40 price difference, and the lower just isn't a major factor in the price of an AR-15. The bolt carrier group alone around almost double the price of a stripped lower. New Frontier seems to be hitting a good price point with their lowers, but theirs include the fire control group (and that's another component that will need to prove itself over time). As far as weight goes, most people don't have weight as a major issue with their AR-15s. Cavalry Arms had a really decent lightweight lower/stock unit, but they weren't able to make a business out of making them... lightweight builds are still a niche market in the AR world and are likely to remain so. There's no point in saving a few ounces on the lower if you're going to put a low end railed handguard on that's going to put all that weight and more right back on the rifle.

August 18, 2012, 07:09 PM
All good points.
Perhaps its use in the SCAR and Bushmaster ACR is because it provides some sort of advantage with the modularity of the weapon system- together with a bit of weight savings.

It sure isn't to meet a "price point".

August 18, 2012, 07:49 PM
My only problem is I can get a stripped quality metal lower around $100 or under by watching for sales. Then pick up a LPK for around $45.00. I have seen videos of torture tests where they do fine then I have seen pics and videos of them break near the front pin, rear pin ,stock near the receiver. and cracks on the front of the magazine well.

Has anybody here had one break? Did the seller replace it or give you a ration of bull that you were abusing it. I know we have this thread. A sticky where just actual users can post their result with them would be interesting. I am not against the idea of a polymer lower and would like to see the actual results from actual users.

August 18, 2012, 08:53 PM
Perhaps its use in the SCAR and Bushmaster ACR is because it provides some sort of advantage with the modularity of the weapon system- together with a bit of weight savings.

It sure isn't to meet a "price point".

No kidding there, that's for sure. Those were what I was thinking of when I pointed out that polymer really came into its own in the handgun world when it was incorporated into new designs. The handgun market was ripe for a rework.

For military rifles, adoption of designs tends to be rather few and far between, so it's just harder to break into that market. The civilian market alone seems to be unable to support a new design on its own and police departments aren't buying enough to make much of a difference. So while there's new designs showing what can be done, they seem to be having a difficult time getting much adoption.

Of course, I think the price issue isn't helping those rifles... when it costs 2-3x a comparable forged aluminum rifle (AR-15 and AR-10 families), the newer designs, even with their assorted advantages, seem to be a tough sell. It isn't enough to be innovative or improved if the old faithful can be plenty good enough at a fraction of the price.

August 18, 2012, 08:56 PM
How did they break, not where but how? Do you have links to those vids?

Let's get this straight. Real world Joe Schmoe buying this isn't taking this into battle. They'll sit in a safe/cabinet and taken to the range or on hunting trips.

I bet mine see's more range duty than hunting duty regardless and that's the unfortunate fact.

I'm betting from what I have seen these are worth the money and will probably end up with a .50 Beowulf less optics for sub $800.00 at this rate, which is great to me.

For the "aluminum stripped lowers" that are this price or cheaper, what guts are you putting in? In what threads would we be cast away or looked down upon because it's not "brand X"?

It seems like it's a loose loose depending on what your spin is, but I suppose that's the internet.

I'll take any more info on 'em that's real world, although I think for the average shooter/hunter/sportsman these will work great.

August 18, 2012, 10:20 PM
"...My only problem is I can get a stripped quality metal lower around $100 or under by watching for sales. Then pick up a LPK for around $45.00..."

The New Frontier lower can be had as a complete lower...that is, lower, fire control group, buffer and stock...for $109. I bought mine from JoeBob Outfitters, which had free shipping. My rifle club FFL does not charge for transfers, so my complete cost was $109.
The Bushmaster upper I used was bought two years ago off ARFcoms equipment exchange, slightly used for $150 (I think).
Altogether, my polymer lower AR came in, as a complete, shooting rifle for $350.
That was before I started buying foliage green Magpul stock components, used, off various traders, for cheap. I will recoup some of that selling off some of my old stock parts.
If, like me, you have an extra upper and BCG to swap on another rifle, for $109, you have a complete second rifle.

August 21, 2012, 06:36 PM
The FN SCAR 16 and Bushmaster ACR also do not have buffer tubes. The buffer tube is the weak point in polymer AR lower receivers. It's the thinnest part, and it has the full force of the bolt carrier group slamming back into it. The SCAR and ACR use a short stroke piston system, similar to an AK rifle. That is how they can have folding stocks.

August 21, 2012, 08:35 PM
The buffer tube is the weak point in polymer AR lower receivers.

I don't know that I'd say it's the buffer tube that's the weak point, but rather it's specifically the area there where the rear takedown pin spring and detent tunnel through the receiver to that takedown pin hole. It's thinner, and with the lower receiver making that angle up to the buffer tube attachment, it's prone to breakage if it isn't strong enough. The few pics I've seen of busted polymer lowers all were broken at that point.

However, as I said earlier, if the maker recognizes this it's easy enough to beef up that particular spot so it isn't near as weak. It looks to me like that's exactly what New Frontier did. If you incorporate a new material to an older design intended for a different material, you can not often do that without slightly altering things to ensure potential fault areas are strengthened. Do that, and you're fine.

August 22, 2012, 05:09 PM
nobody mentioned calvary arms. I have shot few years with no problems. it comes with stock in my opinion makes it stronger.

August 23, 2012, 12:42 AM
They got stung by the BATFE in 2010.

I'd swear I read that someone purchased their assets, but I don't remember who.

August 23, 2012, 09:56 AM
Yeah, Cav Arms made a really neat lower that many folks loved for lightweight builds... I'd not heard one bad word about them, but to my knowledge they are no longer in production and existing stock is really hard to come by now.

Unfortunately, by the time I got around to working up a lightweight rifle, they were long gone. :(