Polymer Lower Recievers

[Ben64]

Guys,

I am in the process of choosing and buying items for my AR built. I would like to use every possible way to reduce weight (carbon fiber hand guard, titanium bolt carrier....).

One of the ways I am considering is to use polymer lower receiver like this one:

Lower Receivers | Receivers at Brownells

Brownells is your source for Lower Receivers,Receivers at Brownells parts and accessories. Shop our vast selection and save!

www.brownells.com

This one is just an example and by no means I am endorsing or advertising it. Anyone here has had experience with polymer lowers? How are they in terms of durability and functioning?

 

[oldfatguy]

NO. The softest aluminum lower is much better then any polymer and weighs 8 5/8 oz (finished). If you have a drill press finishing an aluminum 80% is not difficult. Save weight elsewhere.

OFG

 

[D̷e̷v̷i̷l̷D̷o̷c̷A̷Z̷]

I’ve got a Plum Crazy Polymer lower. It’s lasted longer than the company.

Also have a New Frontier Armory poly lower (I think that’s what Plum Crazy later became)

While they get a lot of flack I’ve not had a problem. Both are “truck guns” and live a pretty disrespected life. They get loaned out and abused. Many 1,000’s of rounds have been shot through em. Never had a problem with either.

Bought em post Sandy H and just needed something.

Hope that helps.

 

[triumph001]

Guys,

I am in the process of choosing and buying items for my AR built. I would like to use every possible way to reduce weight (carbon fiber hand guard, titanium bolt carrier....).

One of the ways I am considering is to use polymer lower receiver like this one:

Lower Receivers | Receivers at Brownells

Brownells is your source for Lower Receivers,Receivers at Brownells parts and accessories. Shop our vast selection and save!

www.brownells.com

This one is just an example and by no means I am endorsing or advertising it. Anyone here has had experience with polymer lowers? How are they in terms of durability and functioning?

I started down the same rabbit hole once. Stopped once I saw what it was going to cost for carbon fiber and titanium. Best durability for a plastic lower is a cavalry arms cav-15/gwacs armory lower. I got as far as buying a cav-15 for my lightweight build. Plenty durable and lightweight, I have fired mine quite a bit with different uppers and its been reliable with all of them. To me one advantage was I didnt need to buy a stock for it. That feature is what makes it more durable than the traditionally shaped plastic lowers.

Cavalry sold out to GWACS which looks like it has been shut down but there are still a number of both brands of lowers out there. Some more reasonably priced than others.

 

[The DFC]

Aren't SCAR lowers poly? They seem to have a pretty good track record durability wise no?

 

[bfoosh006]

KE ARMS LLC AR-15 KP-15 COMPLETE LOWER RECEIVERS AMBIDEXTROUS POLYMER | Brownells

What makes this lower different than its counterparts? The answer is simple… the KE Arms KP-15 is a monolithic polymer AR-15 ambidextrous ...

www.brownells.com

I'd be tempted to try one of these.

That said.. aluminum just works.

 

[triumph001]

Aren't SCAR lowers poly? They seem to have a pretty good track record durability wise no?

Never handled a scar but from what I have seen they do come from FN with a poly lower. But they don’t have the buffer tube boss molded into the back like the ar. Screw a 12” lever into a relatively small piece of molded plastic and you have created a potential failure point. That is where the ogriginal style plastic ar lowers seem to want to fail. You can buy a aluminum aftermarket for the SCAR. Funny how what was originally made from aluminum we are trying to make from plastic and what was originally made from plastic and we are finding aluminum solutions to replace with.

I hadnt seen the KE arms mk3. I like it and for 90 bones at brownells it might be worth looking into once they prove not to be vaporware.

 

[Ben64]

The KE MK3 I posted is a continuation of the cav-15/gwacs design, and I would preorder one if I didn't already have a 5 pound "AR".

Aren't SCAR lowers poly? They seem to have a pretty good track record durability wise no?

True, however, I am not sure if these are made with the same high quality material. Glock, HK G36....they all use polymer extensively.

 

[Ben64]

KE ARMS LLC AR-15 KP-15 COMPLETE LOWER RECEIVERS AMBIDEXTROUS POLYMER | Brownells

What makes this lower different than its counterparts? The answer is simple… the KE Arms KP-15 is a monolithic polymer AR-15 ambidextrous ...

www.brownells.com

Thanks for the link, but I am planing to get a carbon fiber stock. Something like this

Carbon Black STOCK - Brigand Arms

Reduce weight and improve cheek weld with the Carbon Black buttstock for AR-15. At only 4.3 oz (locking nut and plate not included), the Carbon Black Stock is an excellent choice for lightweight builds. Formed from continuous carbon textile, the seamless composite has no failure points and no...

brigandarms.com

Or this

LANCER SYSTEMS AR-15 LANCER ROUND CARBON FIBER STOCK FIXED | Brownells

The Lancer Systems Fixed Round Carbon-Fiber AR-15 Stock is designed for use on AR-style .308 and AR-15 rifles, giving them a solidly built buttstock that fits on any standard rifle-length buffer tube. The stock is available in both A1 (10.25-inch)...

www.brownells.com

And this

https://brigandarms.com/wp-content/uploads/2018/01/Brigand-Arms-Product-Photo-Template.png

I realize they are more expensive but every ounce counts when you have physical limitations.

 

[triumph001]

Seems like you have done your research. What is your intended use and target overall weight?

 

[loveha]

Rather have a V7 or F1 Firearms receiver set than what is essentially plastic.

Also have a look at Smoke Composites.

Carbon Fiber Smoke Composites

Smoke Composites makes advanced carbon fiber AR, PCC and 308 components. Free-floating hand guards, butt stocks, and more. Lightest in the industry.

www.smokecomposites.com

I have the 17" Faxon Firearms carbon fiber hand guard with a V7 titanium barrel nut. I wish I had gone with the Smoke hand guard at a custom length. The two nut clamp on the Faxon just gets in the way of a mag well grip, but it's just nitpicking.

I have the Smoke stock with the closed shoulder, cheek rest, buttpad upgrade, in rifle length. They sell a carbon fiber spacer that goes in for carbine buffer use. Also use their castle nut and carbon fiber buffer plate.
The other two buffers lack things, like a place to mount a QD cup for a sling, or need a buffer tube which adds weight. I looked at both of those when I built mine.

With all that said, with the F1 Firearms skeletenized receiver set, skeletonized Cryptic coatings BCG, Master of Arms adjustable titanium gas block, 12.5" Proof carbon barrel and the afformentioned stock and hand guard. It's just a stupid expensive range toy or hunting rifle IMO. Nothing I would feel comfortable grabbing if my life depended on it.

Take the bipod and RRS rail it's 7 lbs 10.3 oz. Remove the Sandman Ti can it's 6 lbs 6.9 oz, but then I would need a shorter hand guard. Can I make this lighter, yea sure, but not at the expense of comfort.

 

[diablodawg]

I have 3 Tennessee Arms lowers for some lightweight builds. Metal reinforced sections on high stress points, lighter than aluminum and durable so far. Took one on the SAC twice, no issues. Looking to get an AR10 sized for a lightweight hunter build,

 

[Yondering]

I bought 4 Tennessee Arms lowers at one point. They are junk, and the customer service revealed pretty quickly that nobody at the company knew all that much about ARs, and all their development work at that time appeared to be based on one rifle. I got rid of them and would not recommend them to anyone I liked.

The P80 lowers are better (if you don't mind the DIY thing) but still, it doesn't save all that much weight and I prefer an aluminum lower.

 

[NighthawkCG]

I’ve got a Plum Crazy Polymer lower. It’s lasted longer than the company.

Also have a New Frontier Armory poly lower (I think that’s what Plum Crazy later became)

While they get a lot of flack I’ve not had a problem. Both are “truck guns” and live a pretty disrespected life. They get loaned out and abused. Many 1,000’s of rounds have been shot through em. Never had a problem with either.

Bought em post Sandy H and just needed something.

Hope that helps.

Pretty much the same. Have had a New frontier for about 8-10 years. Like said above - it is my beater. Never had a problem with the lower iteself.

It came with some plastic parts (pins, detents, hammer). Hammer eventually wore down enough from BCG that it would just not engage the sear when fired so it went into an unintentional fun mode. Changed hammer and other parts to real metal and no problems.

The only other problem I could potentially see (guessing here - nothing that I know of to back this up) is egging out of the hammer or trigger pin hole. Mine is holding up like a champ, but its something I am watching as in my mind, the polymers are still "new". Older dog, newer tricks...

 

[krw]

I’m sure there are different blends of polymers, and some would be better than others. I wish some “name” brand would come out with a “quality” polymer lower. Hello Glock!! Dont see why it could not be as good as an alum lower, cheaper, and lighter too

 

[The DFC]

I’m sure there are different blends of polymers, and some would be better than others. I wish some “name” brand would come out with a “quality” polymer lower. Hello Glock!! Dont see why it could not be as good as an alum lower, cheaper, and lighter too

I can't imagine how many Glock lowers would sell-it would be an insane number I'd bet. I'd buy one just to have.

 

[ddavis]

From the research I've done it's tough to design an "AR" lower in the form of a Mil-spec aluminum receiver out of plastic because the buffer tube area just wasn't designed to be made of plastic. I ordered one of the KE Arms lowers from Brownells months ago. I emailed KE and they said they lowers should ship sometime second quarter. By all accounts the GWACs/etc lowers were pretty well made. This rifle will pretty much just be a lightweight toy. Not doing any wonder materials other than a CF handguard and pencil barrel to save weight. Basically the Inrange WWSD build idea.

-Dan

 

[E. Bryant]

From the research I've done it's tough to design an "AR" lower in the form of a Mil-spec aluminum receiver out of plastic because the buffer tube area just wasn't designed to be made of plastic.

That's the area which would scare me from a strength standpoint, and it furthermore would be a bitch to mold properly. Assuming that the part is gated somewhere around the mag well or trigger well, there would be a nasty knit line formed around the top of the receiver extension boss.

Given the fact that the part typically operates at/near normal temperatures in a typical semi-auto application, there are some resins which would be interesting to consider. Take some Mitsubishi Reny with 50% glass, design some extra cross-section around the receiver extension boss, get the tool design spot-on; it's possible to make a decent part that would work well for most users. But the design and tooling expense would be considerable, and I'd be hard-pressed to call it a superior part to a typical 7075 receiver. Reny is about 40% lighter than 7075, but some of that weight savings would be lost to beefing up the cross-section in certain areas, so ultimately I don't feel like it'd be a worthwhile activity.

And if people insist on continuing to mold the same cross-section using Tupperware-grade plastic, well, these things will continue to be a disappointment.

 

[Slab74]

Guys,

I am in the process of choosing and buying items for my AR built. I would like to use every possible way to reduce weight (carbon fiber hand guard, titanium bolt carrier....).

One of the ways I am considering is to use polymer lower receiver like this one:

Lower Receivers | Receivers at Brownells

Brownells is your source for Lower Receivers,Receivers at Brownells parts and accessories. Shop our vast selection and save!

www.brownells.com

This one is just an example and by no means I am endorsing or advertising it. Anyone here has had experience with polymer lowers? How are they in terms of durability and functioning?

I’ve run a polymer lower on my 6.8 hunting rig for 6 years. Never had an issue. I also own several glocks, so there is that.

 

[Yondering]

That's the area which would scare me from a strength standpoint, and it furthermore would be a bitch to mold properly. Assuming that the part is gated somewhere around the mag well or trigger well, there would be a nasty knit line formed around the top of the receiver extension boss.

Given the fact that the part typically operates at/near normal temperatures in a typical semi-auto application, there are some resins which would be interesting to consider. Take some Mitsubishi Reny with 50% glass, design some extra cross-section around the receiver extension boss, get the tool design spot-on; it's possible to make a decent part that would work well for most users. But the design and tooling expense would be considerable, and I'd be hard-pressed to call it a superior part to a typical 7075 receiver. Reny is about 40% lighter than 7075, but some of that weight savings would be lost to beefing up the cross-section in certain areas, so ultimately I don't feel like it'd be a worthwhile activity.

And if people insist on continuing to mold the same cross-section using Tupperware-grade plastic, well, these things will continue to be a disappointment.

Or people can do dumb stuff like Tennessee Arms setting the rear lug off to one side in their lowers. I went back and forth with them for a while on that, and they couldn't understand why it was an issue that my bolt carrier was dragging against one side of the buffer tube, since their one test rifle didn't do it. Those lowers were a disappointment and not even worth the $25 transfer fee to my dealer.

 

[E. Bryant]

Or people can do dumb stuff like Tennessee Arms setting the rear lug off to one side in their lowers. I went back and forth with them for a while on that, and they couldn't understand why it was an issue that my bolt carrier was dragging against one side of the buffer tube, since their one test rifle didn't do it. Those lowers were a disappointment and not even worth the $25 transfer fee to my dealer.

Molding a complex part like an AR lower with acceptable dimensional tolerances is not an easy task, especially if one is using cheap tooling and the wrong resin. With some work, it'd be possible to turn out a quality product for a few dollars per part, but the up-front costs to get to that point would be quite formidable. It doesn't take long to get into the six-figure range by the time the design and analysis is completed, the tool is built, and the process is perfected. in a world where aluminum receivers retail for $50, that makes for a tough business case.

 

[Yondering]

Molding a complex part like an AR lower with acceptable dimensional tolerances is not an easy task, especially if one is using cheap tooling and the wrong resin. With some work, it'd be possible to turn out a quality product for a few dollars per part, but the up-front costs to get to that point would be quite formidable. It doesn't take long to get into the six-figure range by the time the design and analysis is completed, the tool is built, and the process is perfected. in a world where aluminum receivers retail for $50, that makes for a tough business case.

Agreed, but in the case of TNA, it wasn't a mistake, they set the rear lug to one side on purpose to put more material around the detent hole for the rear takedown pin. It wasn't the right fix to the problem of course (especially given they are still prone to blowing out that detent hole), but that was their solution.

 

[Blutroop]

Check out fostech. They bought the rights of mag tactical that made magnesium lowers.
I’ve owned cav-15, pof (bought out by bushmaster) and plum crazy. I’m still using my plum crazy lower with a hyperfire trigger and a 26” 17 Remington barrel as a winter coyote gun. I’m plenty rough on it and used it to break my fall on the ice plenty and it just hasn’t let me down yet. I have a mag tactical for if/when it does.
also something to think about is as you lighten the rifle recoil will be more.