History of the Monolithic Polymer AR: From Colt to KE Arms

Today we are taking a look at the history of the monolithic polymer AR-15 lower receiver. By “monolithic” I mean a design which integrates the receiver, grip, and buttstock all into a single unit, rather than the various attempts to simply make a standard AR receiver out of polymer. This is important because the original design of this part does not allow for it to be simply copied in polymer, as the result will be too weak. However, polymers (specifically glass-filled Nylon) have many beneficial properties including light weight, flexibility, and rapid manufacturability which can be harnessed for an AR lower when the design is made to properly accommodate the material’s reduced strength compared to aluminum.

This concept began with Colt in the late 60s or early 70s, and we have one of Colt’s original prototypes to take a look at. Unfortunately, Colt’s material was not up to the task, and the idea was quickly abandoned. It was brought back by the Cavalry Arms company in 2000, who would build a successful line of monolithic polymer receivers in two major configurations until 2010. At that time legal problems forced the owner to surrender the company’s FFL, and the tools to make the receiver were bought by GWACS Armory. GWACS left the design unchanged and restarted production briefly, and their inventory of receivers lasted until 2018, when the new interest in the product form the “What Would Stoner Do” project on InRangeTV caused them to sell out.

At this point, GWACS was unable to restart production, and eventually KE Arms decided there was sufficient market demand to justify the cost of developing a new monolithic polymer receiver that would finally fix the problems inherent to the Cavalry Arms design (as produced by both Cavalry Arms and GWACS). Their new KP-15 lower has now provided the benefits of polymer material that were unavailable to Colt 50 years ago with the engineering that was never properly done on the CavArms/GWACS receivers.


  1. Did COLT bought “intellectual property” to all ArmaLite designs or only AR-15 specifically? If first this would also include very first AR, namely AR-1
    which sported furniture made of fiberglass, stuffed internally with foam. Could this be used in Colt’s prototype monolithic considering its properties?

    • They sold the AR-10 and AR-15 design to Colt in 1959. (The design originated in 1956/57)
      At some point before that they also licensed the AR-10 to the Dutch company Artillerie Inrichtingen.

    • This sounds like something made just for stock, as there are no other parts of AR lower that can be filled with foam.

  2. It looks like the original “polymer” lower is not a damn thing polymer, but an epoxy-fiberglass composite.
    Not surprisingly, when they tried to replicate this polymer casting, it turned out to be crap.
    Exactly the same story was with AK mags.
    And with a Tavor shell.
    And … substitute what you want.

    • Initial Australian AUG frame/body production. Three complete runs rejected due to cracking.

      Furniture of Enfield L86 rifles. Needed to be held together with 100MPH tape, tended to melt when exposed to standard issue mosquito repellent.

      Early M16 buttstocks and handguards. Also required 100MPH tape, especially the handguards.

      Making “stocks” out of polymers is a very exacting business. If the choice of material and its chemical formulation isn’t exactly right, no matter how good the design is, it’s going to fail under load.

      The parallels to making the skeletons of large structures like sports stadiums from wood rather than metal are obvious;


      Metal is considerably more forgiving of mistakes than most “softer” materials.



      • “Polymer” is a very generic term.

        Some polymers can be recycled – particularly the thermoplastic ones.

        Some (but not necessarily all) of the thermo setting and the catalytic polymerised stuff – much less so.

        Then there’s the thorny issue of what fillers and or reinforcement might have been added.

        The actual polymer tends to be more expensive than some mineral, ceramic (including glass) or even vegetable materials

        And those filler materials can contribute useful physical properties, as well as being cheaper than the polymer

        Even materials like precipitated calcium carbonate, can provide useful reinforcement, more flaky or fibrous materials can be even better reinforcement, so long as the polymer wets and forms a bond to the surface of the mineral particles.

        Fibrous material, such as cellulose fibres, can be particularly useful for imparting fracture resistance. Phenol formaldehyde resins alone are too brittle for most uses
        However reinforced with a wood dust filler, “bakelite” is reasonably tough and durable
        With linen or cotton cloth reinforcement/filler, “Micarta” is extremely durable.

        Phenol formaldehyde resins have a lot of cross linking, and once the exothermic reaction to polymerise the mix has occurred, theres not much that can be recycled.

        Epoxies (it’s the epi-oxygen bond that forms the cross linking and allows the polymerisation) likewise tend to be a one shot thing.

        Now add in some directional reinforcement, for example ceramic or carbon fibre threads or woven cloth

        And the object becomes almost impossible to recycle.

        Actually, tyres tend to be almost impossible to recycle economically
        The steel and cloth reinforcements in the structure, render the rubber too difficult to recover at any sort of reasonable price.

        Hence the use of bales of tyres for erosion protection on river banks.

        I’ve even seen the tackle at a cement plant, to sling old tyres into the appropriate part of the rotary cement kiln, to burn completely and fuel the kiln.
        That was one of the few ways to get something useful from old tyres
        Heat, and a little bit of iron that combined to produce tri calcium ferrate, one of the components of cement.

        I think that the cement plant either got the tyres free of got paid to take them, along with things like waste solvents from paint manufacture.

  3. If it was nylon, they almost certainly used ultrasonic welding. If it was ABS, they could have easily used solvent welding. For a prototype, they may have just used epoxy.

  4. Those Sabre lowers made me Salesman of the Quarter @ my LGS when they blew out their remaining stock of the majority (perhaps all) of the Sabre lowers produced – 5 lowers/$100. I put the special on ARFCOM, and their phones went crazy. They then blew out all the remaining blems – cracks, rotating buttstock nuts, or missing takedown pins – 20 lowers/$100. I felt like Oprah that year at Christmas – You get a lower! You get a lower!

  5. The whole point of polymer casting is to reduce labor intensity and cost.
    And here, in addition to the cost of the casting mold itself, the extruder, the polymer itself and other things, you also need welding and so on.
    All together, too long and expensive. It doesn’t matter if it is a small series or a large one.
    Perhaps for mass production, you can develop a form from which the finished product comes out immediately.
    But the cost of this form can only be justified by really large volumes.
    And it will still be plastic and not metal.

  6. And everything could have turned out differently if they had not tried to accurately reproduce the external contours of the prototype…

  7. While the idea might have been great in 1970 when Colt was the only manufacturer and cranking out lots of rifles for the military where the cost and weight savings would have been multiplied over many units it seems that in today’s consumer based market the limitations of a set design for the butt stock and grip would limit the desirability of a fixed design. Today’s consumer wants to customize their AR-15 and often re-customize it over time and this design limits that – Barbie doll syndrome. Unless KP can offer a significant cost reduction and/or ways to offer variations it may find that they are stuck in a niche market.

  8. The first thought in this regard is “why an integrated handle?”
    This makes the molding form noticeably more complex and reduces the custom settings, Don L talks about.

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