Monolithic Polymer AR-15’s (KP-15)

Apparently I am destined to speak on Polymer today more than any other topic.

Polymer80 Kits, took direct legal fire last night and I got further confirmation that my hypothesis (that it is the fact P80 BBS is sold as a ready to complete kit) is the source of the complaint. There are a few ways to ‘solve’ this depending on what the ATF is driving at but that is for a different discussion.

Right now let’s join Ian on Polymer AR-15’s, ones with serial numbers and that are firearms from the factory.

I jumped into the polymer lower game a few years ago when New Frontier Armory released what was a very fair but unsuccessful attempt at making it viable. They broke, mine personally didn’t but several bought on my recommendation did and I very quickly went back to 7075-T6.

Polymer is obviously a viable firearm material. It has worked in handguns for decades and rifles that were designed around it, like the SCAR or G36, work very well too. The problem came in when shoehorning materials in place of other ones without accounting for where a firearm takes stress, like why we cannot use aluminum for gun barrels. Shape isn’t the only thing a material is required to maintain.

So AR-15 Polymer never really caught on because the parts were load bearing, aluminum could withstand it that load, and the cost savings simply wasn’t there between the two materials as a ‘Mil-Spec’ lower.

But, as Ian shows us in the video, Colt knew some of that. Not like we know today, but even back then the goal wasn’t just make the lower polymer, it was to simplify the lower assembly into a much smaller number of parts. Less parts equals less failure points (if the simplified part holds up) and less logistical complexity. It means whatever parts get rolled into the simplified part are no longer a cost factor or a supply liability. Its for those reasons that companies consistently try and ease the cost burdens of manufacturing in ways that do not, or do not within acceptable margin, compromise the product. This works out with varying degrees of success (or lack).

What Would Stoner Do?

There was a bit of kerfuffle on the Social Medias about this being the end of the WWSD project and people adamantly (and accurately) point out that we have an answer for ‘what would Stoner do’ from after the AR-15’s development and sale to Colt.

Eugene Stoner went on to work with Knight’s Armament Company, and the SR-25 and SR-15 resulted. So that’s obviously what Stoner would do because he did, right?

Not so fast friendo (and yes it was a friend who raised the KAC banner) I think we are under representing the point of what the WWSD project looked to do. It was recreating the original AR-15 concept in modern terms and materials, not playing off the heavily evolved M16 and M4 iterations. Yes, Knight’s is what Stoner did. But I believe the KP-15 is strongly in line with what Stoner, Fremont, and Sullivan would do from a blank slate perspective and not a product improvement perspective.

It’s tinged heavily subjectively because we are both allowing and omitting certain tech. Current trends suggest the AR-18 type operating mechanism to be, internally, what is desired and we are not going to divorce ourselves from ancillary equipment like PEQs and lights any time soon. WWSD was a thought exercise, and good one, and this was a concise answer. It is not the only answer but it is a logical one.

So should you avoid buying the KAC SR-15 and get a KP-15 to build out instead?


I encourage getting one of each to cover your bases. However from a cost efficiency perspective, building out a KP (even adding some Knights parts) is going to be a very attractive base. The compromise is basically limiting yourself to a fixed stock and pistol grip, minor items when considering a generically efficient light fighting rifle.

Keith Finch
Keith is the Editor-in-Chief of GAT Marketing Agency, Inc. A USMC Infantry Veteran and Small Arms and Artillery Technician, Keith covers the evolving training and technology from across the shooting industry. A Certified Instructor since 2009, he has taught concealed weapons courses in the West Michigan area in the years since and continues to pursue training and teaching opportunities as they arise.