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.