US Arms Polymer Lower

AR/M4 AR General Discussion
1

Last year, I was poking around on a high traffic firearms site when a company rep came on asking members for volunteers to run a polymer lower through it’s paces. I contacted the rep by PM and told them I’d be willing to buy one and run it as hard as I would a forged aluminum receiver and would report the results honestly. The rep got back to other members who volunteered but my request was ignored and I griped about it here on m4carbine.net. Brian at US Arms saw my complaint and contacted me to ask if I’d like to evaluate their new plymer lower. He said I was welcome run it hard and report the results- warts and all. Though skeptical about plastic lowers, I agreed to give them a fair shake. http://usarmsllc.com/Patriot-15.html

I expected a stripped lower, but they sent me one that was complete. Everything is polymer except the FCG, pins, springs, castlenut and end plate and buffer. That’s right, the FCG is metal, including the hammer. The receiver extension is also polymer and is molded to the commercial pattern. I think US Arms would do better if they used the mil-spec dimensions.

The receiver seems stiffer than other polymer lowers I’ve looked at. The fence on the right side that runs from the front receiver pin to the mag release has been made thicker for added strength and rigidity. There is also a fence running around the mouth of the mag well which is flared without being too big. The lower comes with an integral trigger guard which has a large opening. Stock is of the M4 style and has a surdy polymer sling loop. The RE has six positions. Buffer has no markings so I assume it’s carbine weight. I assume the action spring is of the standard variety.

Standard AR triggers run from atrocious to decent. This trigger has the usual gritty creep, is a little on the heavy side but has a surprisingly crisp break. I haven’t taken the time to pull the FCG out and grease it up but I think it will be fairly nice once I do. As tested, MSRP for a complete lower is $199. It’s $89 for a stripped lower. PSA is offering a complete polymer lower for $129

I borrowed a 16" upper from a PSA carbine to test this lower with. The receiver pins are a little stiff and need a tool to push open. Fit around the back of the upper is a little off. There is a small gap at the curve but where it’s vertical, it fits a bit snug. The good news is that for those who worry about such things, there’s no rattle!

The complete lower M4 style stock weighs in at 1 lbs, 12 oz. In comparison, a PSA lower with a S&W made M4 stock weighs in at 2 lbs, a weight savings of a quarter pound. A PSA upper with an Aimpoint H1 Micro, Surefire x300 weapon light, Mossie Tactical light rail and round mid-length handguards was used to test the US Arms polymer lower. The whole package weighed in at 6 lbs, 11 oz. The same upper on a PSA lower with M4 stock weighted in at 6 lbs, 15 oz.

There was a little binding towards the end of the travel when cycling the action. A couple rounds of 55 gr American Eagle did not completely go into battery during firing. However, after I added a few drops of oil to the BCG and the problem went away. Maybe it was the drag, maybe it was a dry BCG, maybe a combination of both. Because of the weather, I was only able to fire one mag. What first struck me was the carbine felt lighter and livelier even with the weight shifting towards the muzzle. I still dislike the duckbill of the A2 pistol grip and don’t like black furniture. I didn’t notice the M4 stock being uncomfortable compared to the Magpul CTR but a longer shooting session might change that impression.

The receiver has clean edges and corners and is without distortion. The surface has a matte finish that matches the PSA upper well. There is more flash at the mold line than there should be and the only mag that drops free is the Lancer L5. Magpuls, Troys and GI mags need to be stripped out. There is more stiction than usual between the stock and RE but nothing to preven the shooter from easily making adjustments.

I contacted Brian at US Arms about my concerns. He said they are tightening up QC and expressed concern the flash and tight mag well made it past QA. He also told me I could return it so they could address the problems. He’s dedicated to making this right.

A few other items of note: Adjusting the windage and elevation of an Aimpoint Micro in a cold rain is very awkward. Removing the small caps with stiff hands was difficult and I worried I’d drop the cap and lose it.

The plastic of the IO cover is stiffer when it’s cold. When I popped the caps off the lenses, they didn’t flip out of the way. I had to snap the covers together to see through the sight. The caps did an excellent job of keeping the rain off when snapped closed over the lenses

Every rifle should have a sling.

Hats with full brims rock. Never leave home without your jacket.

In full disclosure, I did not buy this lower. US Arms sent it to me (via a local FFL, Quantum Guns in Spanish Fork Utah) without charge, for evaluation. Other than them sending me this lower, I have no other connections with the company, financially or otherwise.

As weather and time permits, I’ll continue putting this lower through it’s paces. I won’t baby it, but I’m not gonna set out to see how much it’ll take before it breaks. It’s advantages over other polymer lowers is increased stiffeness and a metal LPK. It’s advantage over an aluminum lower is a weight savings of a quarter of a pound. MSRP is higher than than some other polymer lowers, but street pricing should make them more competitive. Whether or not they prove to be durable enough, only tine will tell. I’ll give updates with my findings

2

Having lost a rifle on a canoe trip I am interested in a cheap, lightweight rifle that would not break my heart if lost. I will follow your reports.

3

Well written report.

For $200, right now you can by a complete lower half with a forged aluminum receiver. I know it’s not the point of your post, but as a purchaser, my first question would be ‘why?’.

That, and the single biggest weakness in lowers like this, the area between the grip and where the receiver extension screws in. I’m fairly sure that a little bit of army style IMT (Individual Movement Technique) would render it inoperative. Feel free to demonstrate :wink:

Having said that, I’ll take free guns any day.

4

Very interested in seeing how it runs after hard use.

5

Nice write up. Makes me think back to when Glocks were called junk. Thanks for the report.

6

Nice going securing a free lower for testing! Good review so far, I’m looking forward to following this thread to see how it holds up after running it hard.

7

I’ve heard from some people that the weak spot on these is where the buffer tube meets the lower if you have the m4 style stock. Any thoughts on that? I have heard good things about the A2 style polymer lowers given the fact that the lower and buttstock are one solid piece.

8

That was the Cav Arms lower. It strengthened the area where the receiver extension nornally mounts but it had the disadvantgage of having a fixed length stock. I’m not sure they are being made any more

9

I’m curious as well to hear the end result…

Sent from my ADR8995 using Tapatalk 2

10

That’s certainly one of the better looking poly lowers I’ve seen to date.

I imagine at some point someone will figure out the right properties and given the proliferation of scaled down 3D printers we’ll be seeing a lot more of these. Progress of some sort is inevitable.

11

Added link to their web page- http://usarmsllc.com/Patriot-15.html

12

My guess would be that they need the added diameter to keep strength up. Sort of the same reason that standard commercial receiver extensions are larger in diameter in the first place, the material isn’t as strong.

Not really the point of your post but I’ve never believed in “balance.” Heavier is heavier, lighter is lighter. Now if the rifle is going to weigh nine pounds is it better that the nine pounds be distributed in a balanced way? Sure. But is balance worth adding a heavy stock to the rear of the gun? Not so much…

13

GWACS Armory is making the Cav Arms lowers…I guess they bought the molds and rights, or there is some other connection between the two. But they are available for $99 at DSG.

14

Very nice write up… Are you just going to be updating this thread over time?

15

Balance is subjective. Some shooters like a bit of weight out at the muzzle, others like the weight closer to the butt. Some like a neutral balance. I agree that adding weight without some gain in performance is a poor practice

16

It wasn’t that long ago that Glock changed the world with “plastic pistols”. We might see a similar impact in the AR-15 market with polymer technology.

The challenge I see for manufacturers is the fact that the lower isn’t a very expensive component as others have noted. Based on this sample-of-one evaluation polymer saves a little weight but not much cost.

However, lf the day ever comes where our 2nd amendment rights fall, and we have to bury our stripped lowers in the ground somewhere, polymer might be a big win from a detection standpoint.

Thanks for the review and I look forward to more results from your evaluation.

17

As said above, none of these lower companies are addressing the real issue. How long will it take to realize that you cannot use a conventional RE setup on a plastic lower?

Now what I would like to see is a completely plastic lower with the Vltor A5-type buffer tube setup. At that point, you can make it completely solid where the threads should be, and the longer length of the A5 (6 position) would give you more solid material up to the first position for the stock. I feel like that would be a MUCH more durable solution even though the buffer tube is made out of plastic than aluminum.

Anybody else see a problem with my idea?

At the same time, I won’t make judgements against this lower until it has proven itself either way. I’ll keep my eye on this brand.

Edit: I also have another idea. Increase the amount of threads and extend the back end portion of the lower. Then, make a slightly longer buffer tube that is also threaded further down the buffer tube (Maybe an A5 6 pos. with more thread?). That way you’ll have more solid material where the plastic lowers usually break, as well as increased surface area on the threads. Having plastic threads on aluminum threads doesn’t seem ideal, so I would guess even doubling the amount of surface area would make a significant difference.

18

These poly lowers are still evolving it seems. I have seen a couple with weak spots and one cracked. But, with prices starting to settle, lowers are becoming more readily available and at decent prices again.

19

Polymer AR lowers are not analogous to Glocks for one big reason: Glock designed his pistol’s dimensions around the material, but polymer AR lowers are still limited by the original dimensions that were spec’d for aluminum. A polymer rifle receiver by itself could turn out to be the next greatest thing, but a polymer AR receiver has extra challenges created by the constraints of “USGI” specs, and this means they deserve the scrutiny they’re getting.

Thanks for the great report!

20

The dimensions of the Glock frame are not that different from one made of steel or aluminum. Glock engineers simply identified the areas of the frame that needed metal for durability and replaced the rest with polymer.

AR polymer lowers will come into their own when a manufacturer designs one with metal inserts where needed