https://www.youtube.com/watch?v=O3SoZ-Ls_HQ

While packing up my desk for a recent move, it dawned on me that my pen holder of the past eight or so years was actually a New Frontier Armory stripped polymer lower receiver this whole time. A day later and an M16 full-auto fire control group, the appropriate federal licensing, and some curiosity combined to find out if a $22.99 AR-15 lower receiver made of fiber reinforced plastic was durable enough to form the foundation of a machine gun.

Coincidentally I had also just purchased a few ATI Schmeisser S60 magazines (available at Brownells HERE) and figured testing ’em out at full-auto speed was just about perfect.

The S60s loaded up 60-rounds-deep more easily than I anticipated, though for sure the spring system is stiff and once you hit about 40 rounds there’s a bit of a thumb workout involved.

If you’re cleaning these bad boys watch out when you pop that baseplate off! The large spring in the quad-stacked section uncorks like a coked out genie. Keep a handle on it, and keep your face out of the way.

With an old tank of a YHM suppressor screwed onto the business end, I proceeded to dump 120 rounds through the polymer wonder with only enough time in-between magazines to move my camera around. The upper was screaming freakin’ hot, and the finish was burned off about 1/3 of the silencer.

The action shots are in the video embedded at top, of course, but the punchline is that, after the upper cooled down enough for me to touch and remove, the New Frontier Armory lower was absolutely fine. 100% just as good as new in every last way.

Which is not a surprise. An AR-15 lower receiver doesn’t typically have much in the way of demands put on it. It holds the magazine in its place in space, it holds the trigger in its place, and it holds the receiver extension and stock where they belong. Your shoulder is supposed to support the stock under recoil, so even that rear threaded area of the receiver has a fairly easy life if you’re shooting the rifle in a normal fashion.

Frankly, you could (and should) make a lower out of wood and it would be totally fine. Yes, I promise I’ll do it.

Likewise, the ATI Schmeisser magazine performed flawlessly. I did have a failure to fire stoppage somewhere in the middle of the ATI-fed 60 rounds, but the round stripped properly and chambered fully, so it was a trigger or hard primer issue and nothing magazine-related. Since this range day I’ve shot the S60s a bit more and have had zero issues. They appear to feed reliably, feed strongly enough to keep up with full-auto, and are very high quality.

If an area on this polymer lower was going to fail eventually, I believe it would be around the pivot pin. After 120 rapid-fire, select-fire rounds the chamber area and barrel nut area of the upper had heat soaked pretty thoroughly and that heat was beginning to migrate into the pivot pin area of the lower. At some point I believe it would soften up and then begin to melt.

That said, it’s possible that under non-stop full-auto fire the gas tube or another component in the upper may well fail first.

Is a polymer lower sufficient for machine gun use? Yes, yes it sure is. Though I may return this one to pen holder duty.

RELATED ARTICLESMORE FROM AUTHOR

48 COMMENTS

      • We have a polymer lower on wife’s rifle. Very light weight..under 6lbs. Not sure I would trust it going full out like that…

      • When I saw it was from Mattel I felt right at home….. my GI Joe had one too! LOL…. Still think the M14 was a better all around weapon. It could have been upgraded…. but it would still have been an anchor!!

  3. I am so sorry to bring this up, but it really, really knots my Hanes up tightly when a guy like this has the balls to ask people to send him some money so he can buy ammo to shoot on a goddamn video for the rest of us to watch. Poor baby. He even mentions that .223 ammo is in short supply and is hard to get. Well, shit fire to save matches, little boy, but I’ll be damned if you get a nickel of my money so you can have all the fun!

    • I think he should send me the gun, I have a few cans of 5.56, plus I could put on a shorty .300 blk upper and see how that works. Then I could tell him how it worked and he could make a video reading my report!

      • “And you are angry about this.”

        What’s galling about it is, it’s a gun we’re not ‘allowed’ to buy or possess, even if we wanted to put our money down for it.

        The commenter has a valid point, Jon. You seem incapable of seeing it because you have the exact same ‘special’ status he has.

        How about making us ‘Remote Testers’ for your registered toys?

        You have my permission to put me on your payroll, trust, whatever the NFA calls it.. No need for a paycheck, just ship me an NFA toy once a month for a testing session… 🙂

        • Why aren’t you allowed to do it too? Is it that you are not allowed to, or just not willing to put the same time and money into it that we have?
          The whining never ends.

        • If you enjoy watching the free videos and would like to chip in so I can afford to make more videos and hopefully increasingly better videos, that’s great. If not, that’s the norm and no worries. It’s optional. I request it because requesting it helps…think of it like the advertisements you see on every other free media you consume, which is only free to you because the ads pay for it because some of the viewers patronize the advertisers. My range trips to test stuff for TTAG reviews and for videos is a net cost to me, even with the $86 a month or whatever it is that I’m grossing via Patreon. I do it because I enjoy it. However, if I can do it without it costing me money that’s a big help to me, and if it ends up in the positive dollar range then I’ll use those funds to make more, better content. I think that about sums it up.

    • Then I suggest you dont send money or watch said videos.

      Or produce your own videos…..then you’d ask for money and we wouldn’t give it.

      But we probably also wouldnt whine about you asking for money.

    • Then don’t freaking watch it. Simple as that. Many people on YouTube produce high-quality content that requires money and time.

    • Above commenters suggest the video was free, or that we shouldn’t watch it because we aren’t willing to fork money over. Well, It wasn’t free. The the purpose of the video is to keep me coming back here to TTAG, and perhaps click on the ads while I’m here. There are ads littered all over this site. The site has a range of traffic that visits this site per unit time, which creates equity in the site itself. Traffic x Ads = Money.

      So by merely visiting this site, we already gave you some money.

  4. I built a carbine with a polymer lower during the panic of 2012. Worked fine for a while, my son laid it down on the bench at the range, and the stock and receiver extension tumbled onto the floor, cracked right through at the takedown pin. Manufacturer offered to replace it, but with transfer fee and return shipping, I opted instead to buy a forged aluminum lower instead for just a couple of bucks more.

    The manufacturer had since added some metal internally into that section of the receiver, but I swore off polymer AR receivers after that. I’ve never heard of a forged receiver snapping in half.

    • Right at the takedown pin is the most common place for aluminum receivers to crack, too. Just Google cracked AR15 lower receiver and you’ll see tons of ’em, nearly all of which will be right through that spot. Whether FRP lowers are more or less likely to break there is a matter of some debate, and there are probably too many variables to make a blanket statement like that anyway.

    • It’s called stocking up for the hard times. Never be the grasshopper. Always be the Ant. if you’re old enough the Hildabeast scare should have taught you. For some POTG they learned during the Slick Willie Regime. Some of Us even before that.

    • Personal inventory. I don’t have crazy amounts but probably have or at least had like 4k rounds of .223 at my house before all this craziness started. No plans to buy more until things normalize. In the common calibers you gotta stay stocked somewhat deep. In more niche stuff you really don’t, as the stores will always have 6mm Creedmoor and whatever other target and hunting stuff. But the commodity and self defense calibers? You should keep enough to last you at least a year, IMHO

  6. “That said, it’s possible that under non-stop full-auto fire the gas tube or another component in the upper may well fail first.”

    I couldn’t re-locate them, but there are videos out there of an early M16 manufacturer (Colt?) destructively testing pencil and “heavy” profile barrels. The pencil barrel drooped like taffy after only ~10 mags of full auto and the heavy barrel’s gas tube blew out after ~15 (IIRC) mags. My numbers are probably off by a smidge but it was really surprising how quickly they self destructed.

    So, unless you have quite a few uppers to literally hot-swap in you’re probably not going to be melting that lower even with this kind of abuse. But I’d still love to try…

  7. Full auto is fun, but do enough of it and it becomes routine. In the real world aimed rifle fire is more effective. Entry, is probably as easily accomplished with a double tap as two round bursts. Belt fed is another story. Infantry squads should have belt fed machineguns. (The BREN is an exception. The best mag fed LMG I ever fired. Browning BAR a close second.) Anyway, riflemen need suppressive fire on the objective while they flank or do a bounding overwatch. (Should be .30 caliber.) Again, full auto is fun. If you can afford to feed it today.

  8. Can’t see myself ever laying down suppressive fire, but I will admit full auto is something I would like to try out.

    • Rusty, there are lots of commercial ranges that will “rent” full auto weapons. Free advice, go ahead and do a full auto mag dump. Get it out of your system. Most people have to. After that, stance. Just like handgun choose the stance you prefer.Lean slightly forward at the waist. Flex your knees. Get on and off the trigger. Two, three round bursts are what you want. Full auto is fun, but it ain’t no death ray.

  9. I’ve also seen the YouTube video of someone shooting an AR with an acrylic lower. It didn’t last too long, but didn’t fail disastrously.
    But what I’d really like to see is a test of an AR built with a lower machined from Aluminum oxy nitride, also referred to as AlON, also referred to as transparent aluminum. Yes, it is transparent. Makes great but expensive highly bullet resistant windows.

  10. Maybe not Kosher, but I would like to ask if you can just move that giggle switch from rifle to rifle, since the switch is the “machine gun”, and if so, could a person who is not a manufacturer do so? Or is it locked into that lower or upper/lower forever once installed?

    • In this case the lower is the registered part. You could register a drop in auto sear or something and move that from gun to gun, yes, but the standard M16 trigger pack with auto sear are not regulated items. Since you have to cut the lower properly for the auto sear and drill the third hole for it, it’s the lower that ends up being the machine gun. Usually when the part can be dropped into an otherwise unmodified receiver, that’s the case in which the part itself is what’s registered.

      • “the standard M16 trigger pack with auto sear are not regulated items.”

        Really?

        Someone who has one and an AR-pattern receiver won’t get busted for ‘constructive possession?

        • The sellers I’ve seen (at least BCM and even Brownell’s have all the parts on their website) say they won’t ship the parts to you unless you give them a copy of your registration.

          Theoretically it wouldn’t be constructive possession since you can’t physically mount the parts in an unmodified civvie lower, but who wants to chance taking the ride for parts that are effectively just paperweights anyway?

        • I haven’t seen that on Brownells. I believe you can purchase them from just about anywhere without restriction. Here’s the auto sear (https://bit.ly/338BmoJ) and the rest of the M16 trigger components (https://bit.ly/3397Zmm) on Brownells. I did not have to provide proof of my SOT or registration when I bought a few, though I didn’t buy from Brownells as they weren’t in stock but I just got ’em from another online retailer without issue. It’s the lower receiver that requires machining and it’s that process that’s regulated. No third hole allowed!

        • I haven’t actually tried to order those parts, so I defer to your knowledge. Maybe I was misunderstanding something; I couldn’t find the warning I thought I saw on BCM’s site.

      • Boy, that helps, but still leaves me confused. So, as a manufacturer, you are describing the current manufacture of a Class 3 weapon, then the, what, “unmanufacture” of same, and I assume you recovered the select fire trigger group. If you do so again, I assume you cannot sell it to me, only to military, police, whatever. Is that correct? A lot of this unconstitutional paperwork silliness ends up seeming like magical processes, also that it changes every day or two.

        • The lower has the “third hole” drilled for the auto sear. It really cannot be reverted into a legal configuration — it basically needs to be destroyed if I want to “unregister” it. You’re allowed to own all of the M16 fire control group components and can purchase them from all sort of places. You are not allowed to modify your lower receiver to accept the trigger parts (the auto sear), though, without going through the legal process.

  12. “…the stock and receiver extension tumbled onto the floor, cracked right through at the takedown pin.”

    My thoughts exactly. I’ve milled out a few polymer AR 80% receivers and built guns on them in 5.56 and .300 Blk. My primary concern in treating them as much more than toys is the threaded extension that the buffer tube screws into and the material directly below. Not very strong in the original aluminum receivers, pretty flimsy in the plastic ones. As far as I know, there is no metal/aluminum support baked into the poly receiver, none that I can see, anyway.

    As a side on the 80% poly blanks, I ended up with 2 where the provided takedown pin holes didn’t exactly match up with those on the upper so the only way to make them work was to slightly” (but noticeably) elongate the holes. Better in the cheap lower than the upper, IMO. In a call to the maker (which would rhyme with “GD Armory), the rep claimed it must’ve been my machining-obviously not since I didn’t drill those holes and they are necessary points of reference for doing the 20%. Additionally, on the first one when disassembling the upper from the lower, the poly material surrounding the detent and spring for the front takedown pin broke out though I applied scant pressure to press the takedown pin past the detent indentation in the pin. Same rep’s suggestion was to use JB Weld to repair it- there’d be no replacement of the receiver blanks for either issue. These things were only $40 but it was a disappointing experience all the way around. The aluminum 80% receivers have caused no problems.

  13. Yes I have 2 of the pos receivers you are discussing with similar results the composite does not machine like aluminum it tends to want to come out in chunks so to speak even when being gentile usually where a detent and spring will end up . I
    wonder if there is a void or pocket at that area . not sure how molded or if spring detent holes are drilled or how formed .you get what you pay for shows up here.As per the auto kits they are unregulated but drill that extra hole can get ya 20 so be ware.

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