Polymer Lower? Anyone tried one?

[kymasabe]

A few years ago, I built a lower with a New Frontier Armory polymer lower receiver but unfortunately sold it before I had a chance to test it, someone I knew at the time snatched it up. I just ordered another from a private seller, but is NOS and carbon fiber reinforced. I was wondering if anyone's had any good or bad luck with polymer lowers. Yes, I've read the reviews online, looking for first hand experience from my fellow members.
The plan? Polymer lower, Spikes build kit and grip, MFT Minimalist stock, pencil carbine length barrel, nice light B5 handguard and no muzzle device, just a thread protector. I wonder if I can get under 5.5 lb?

[Ricklin]

I wonder if anyone has tried doing a "hybrid" polymer lower? I'm thinking along the lines of metal inserts at high stress areas, like the pins for instance.

How much weight is lost with a polymer lower? Perhaps it's a juice and squeeze thing.

[Screwball]

Polymer lowers based off a stripped AR lower are prone to issues. Most happen at the thin area between the buffer tube and pistol grip.

I only recommend polymer lowers that incorporate the grip and stock into the receiver. Currently, KE Arms is the only game in town… and having one of their lowers, definitely a great buy.

If you watch YouTube, InRange did a long series discussing what Stoner would have done if he redid the AR platform in current times. Their original build used CavArms polymer lowers, which resulted in the stock of them selling out. KE Arms made their own lower, and InRange worked with Brownell’s to make the WWSD 2020 rifles. A lot of good testing and information on the subject.

But from someone that tried it early on (Tennessee Arms), and was out the transfer fee when I returned them back to the manufacturer… you’ll get a functional rifle that won’t break in the end by going with KE Arms.

Zero affiliation with them… just have one of their lowers on a lightweight build. Extremely happy with it.

[zukiphile]

Yes, I've read the reviews online, looking for first hand experience from my fellow members.
The plan? Polymer lower, Spikes build kit and grip, MFT Minimalist stock, pencil carbine length barrel, nice light B5 handguard and no muzzle device, just a thread protector. I wonder if I can get under 5.5 lb?

I believe so. That build with a billet lower, prism optic and large Surefure three prong flash suppressor weighs 5 pounds 10 ounces empty.

I did that with a lightweight BCG and no weight buffer (which will require an adjustible gas block). I also used a carbon fiber free float handguard with a Faxon midlength pencil barrel. It's feathery.

I prefer the NF lowers to the aluminium for everything except slinging up with a lot of weight. They are rattle free and not cold to the touch like metal.

Karl's InRangeTV test was problematic. Doing push-ups on an AR isn't recommended with aluminium lowers, and he never does a pushup on an aluminium or CavArms lower the way he did with the NFA item. i.e. with one hand out at the end of the buttstock. That doesn't mean than NFA are indestructible or that CavArms or aluminium aren't great, just that Karl's testing method indicates a preferred result.

[Crankylove]

I’ve got two Tennessee Arms poly lowers.

.223 lower was a birthday present from one of my brothers. Used it, along with a bunch of left over parts from two of my brothers builds, and a barrel they gave me for Christmas, to build a m-forgery-ish carbine. Poly lower, lightweight barrel, and a red-dot made the rifle quite light. I ran that lower for 4-5 years, before I came across a deal (free) on a Aero Precision lower and swapped the poly out. I had zero issues with it, and still have it sitting in the safe for another build.

.338 Federal lower was an accidental purchase by a family member, who after they received it, discovered they had no desire to build an AR10 style rifle. They offered it to me for a screaming deal (free), so I spent the next couple years piecing it together. It’s only got a couple hundred rounds through it, but haven’t had any issues yet.

Both rifles were built with generic upper and lower parts, leftovers from other builds mostly. Both went together with no issues, and have functioned fine so far.

I’ve heard about, and seen pictures of, cracks around where the buffer joins the frame, but haven’t seen any on mine yet.

I don’t know that I would go looking to buy this style poly lower (and would like to swap out the AR10 lower for aluminum), but given the price I paid, and the zero issues I’ve had thus far, I really can’t complain.

[Cyanide971]

I’ve been very happy with my KE Arms KP15 lower that I have paired with an 16” BCA MLOK upper in 7.62x39. Empty weight with a TA44C Mini ACOG riding on a Midwest Industries QD mount sits right at 6.6# (same as my old Czechpoint VZ58 CQB model with irons). Only have a little over 1k rounds through it, but has been very enjoyable to shoot between myself, other family members, and friends.

[44caliberkid]

I’ve done four polymer lowers. I use a modular trigger like a McCormack or Saber, because it is hard to hold tolerance for the pin holes in polymer, and mil-spec triggers will possibly fire bursts or full auto till the mag is empty. Other than that, all function fine and no problems. I haven’t done an endurance test on one, just casual shooting.

[kymasabe]

Originally Posted by 44caliberkid

I’ve done four polymer lowers. I use a modular trigger like a McCormack or Saber, because it is hard to hold tolerance for the pin holes in polymer, and mil-spec triggers will possibly fire bursts or full auto till the mag is empty. Other than that, all function fine and no problems. I haven’t done an endurance test on one, just casual shooting.

Hmmm. I have a JMT Saber I just got that I dont like, was gonna return it. Now I may keep it to drop in the poly lower....just in case.

[7.62 man]

I have had a composite lower for a few years. I have used it on many uppers .223/5.56 & .300 blackout I have even loaned it out to a buddy to hunt with a .458 SOCOM upper.
The only problem was in the hammer & I had to replace it with a steel hammer/trigger set.
A composite lower will last if you take care of it & don't abuse it.

[Geezerbiker]

I'd be more likely to buy (assuming reasonably priced and if available) a steel or stainless lower. While I've never broken one, they do look a bit fragile...

Tony

[armoredman]

CavArms, my very first AR15. Finding the proper pins was a pain, since they have to be longer. Once we got the minor issues figured out, it worked pretty well. This one is now long gone, gifted to another person to make a youth rifle.

[Onward Allusion]

I have 2. One pure poly and one hybrid. Both go bang but I had swapped out the hammer & pins for metal in the pure poly one. Yes, it even came with a plastic hammer! Was getting light strikes. The only think I would worry about would be the stress points - tube area & right behind the grip.

[The Happy kaboomer]

Right on 762man!
I've used a Plum Crazy plastic lower for many years with ZERO problems.

[NeverEnough]

With how cheap metal lowers are, no point in taking the risk on polymer IMO

[viciouskitty]

I have both a cav arms lower and one of those ati polymer lowers much like the new frontier without the metal inserts. The cav arms lower has been great, it’s my primary match rifle and I use it to compete in biathlon’s. I’ve dragged and dropped that rifle across many many miles and it’s held up rather well. I will say when I installed a cmc packet trigger into the lower I had to cut on the bottom of the trigger well as it was not square in the corners. Besides that no other issues have been encountered.

As for the ATI lower it’s on my wife’s gun, I bought it complete and she’s used it for years though admittedly it does not get run very hard. It works for what we use it for.

[kymasabe]

Update: the Tegra lower receiver arrived, put it together with a Spikes Tactical lower build kit and an Anderson stainless trigger and...its not bad!
It's much stiffer than the New Frontier receiver I built a few years ago. It took a little fitting/filling inside the lower receiver to get the rear tang of the upper to fit properly, but otherwise everything else fit properly and seems to function fine. Mounted a slickside upper with pencil barrel and thread protector instead of a muzzle device and the whole rig is surprisingly light. Just might turn out to be my new favorite.

[Nodak1858]

I've done a number for the Polymer 80 ones. All turned out pretty nice, have them on 22LR, 7.62x39, 5.56 and 450 Bushmaster. None have had any issues so far. Granted not have more than a few hundred round through them, but ok so far. I stopped doing them once I got a mill, now it's all aluminum 80s, but don't see an issue using them.

[dvdcrr]

No polymer lowers here, but I have used a few aluminum ones and they tend to work pretty good.

[MarkCO]

Originally Posted by Screwball

Polymer lowers based off a stripped AR lower are prone to issues. Most happen at the thin area between the buffer tube and pistol grip.

I only recommend polymer lowers that incorporate the grip and stock into the receiver. Currently, KE Arms is the only game in town… and having one of their lowers, definitely a great buy.

Yep, 100%.

I built a few using Cav Arms lower, then GWACS, and recently, a KE. There is some common DNA among those three. The first was 6 pounds, the second was 4.5 pounds and the third was 3.9 pounds (which was a little over the top with LW components). But they are good and reliable.

The others, not even if they were free would I build out a stripped lower of polymer. True, the lowers don't take a lot of stress, but I don't handle my firearms like glassware.

[GeauxTide]

A local vendor, and good friend, that chose to manufacturer metal lowers, so that's what I buy.