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Home » How to Build a 0% Polymer AR Lower Using a Kit: Is it Worth It?

How to Build a 0% Polymer AR Lower Using a Kit: Is it Worth It?


Plastic Fantastic AR-15 IV Lower Build
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I got back into building AR pattern rifles last year and made a couple to meet my personal desires. As always I like pushing the envelop and thought of manufacturing my own lowers for my personal use.

Research into this lead me to cast epoxy lower receivers. I have heard good things about them.  The cost is reasonale.  However,  I do have some reservations to having a plastic rifle.

In the spirit of exploration and trying new things I want to build a plastic fantastic AR-15 and see just how useful a home cast AR lower can be.

Legal Caveat:

I don’t know your state and local laws and I am not a lawyer.

I do know that this is federally legal as long as you don’t build them for commercial purposes or transfer the guns to someone without having serial numbers and proper federal paperwork.

Since this is my gun to never leave my state or my possession it is my right per the Tennessee Firearm Freedom Act to be able to make a legal semi-automatic rifle.  However, there are regulatory restraints within that law as well.

So please watch the Plastic Fantastic AR-15 I Introduction as the first of a 5 part series.


In this video above I show how I went about molding the lower receiver  using the freedom-15 mold kit. This kit is not hard to put together, and it is a pretty ingenious idea.

It is pretty well documented on their website and the kit comes with instructions.

The only thing I found difficult in the molding process is bending the buffer tube support to fit inside the mold.

It was, without a doubt, the most difficult portion of the process. It is also something that caused blemishes in the final product.

I had places where the metal support touched the side of the mold so that it showed through the epoxy on the side of the finished receiver.

This did not impact the final product in terms of usability, it did hurt the lower cosmetically.

Once again I have my doubts about a plastic AR-15 Lower receiver, but if it works it would be awesome to be able to make my own 100% lowers whenever I want. The price of that is not bad. However, it you are looking at straight cost, there are cheaper ways of getting AR-15 stripped lowers.


In part III I focused on Heat Treating the Polymer AR-15. This is am additional step in making the freedom15 lower stronger and is recommended by the manufacturer.

I also compare the finished lowers side by side to show the various shades of black and grey and tell the corresponding numbers of drops of black pigment per lower.

Additionally, I talk about how I broke one of the lowers in the de-molding process and how that happened so you can avoid wasting one of your lowers.

Making these were pretty easy. You can allot about 2 hours per lower, and the company says and one hour and forty five minutes per lower is average.

I took somewhere between the two, but I was closer to 1:45 than 2.

Heat Treating the Polymer AR-15

  • The manufacturer recommends a 12 hour air cure at 70F+ air temps before heat treating the Feedom15 lower receiver.
  • Set a small toaster oven at 135F
  • Insert the lower into the oven so that it sits upright on the mag well
  • Bake for 2 hours.

Heat Treating the Polymer AR-15 is not required…..however the manufacturer states it will make the lower stronger.


This video is a 10 minute instruction on building and AR-15 Lower Receiver. This lower build happens to be on a Freedom15 Polymer lower, so it is a little different.

Building an AR-15 lower is not hard, and can be done with common hand tools in less than 30 minutes, even by a first time builder.

However, building an AR is pretty simple, but sometimes things go wrong and may take a little more to get functioning.



I took the plastic fantastic to Royal Range for the Polymer AR-15 Test Fire. You may remember I went to Royal Range and did a construction video before they opened.

I did like the range setup a lot, but the rifle did not meet my expectations.

It fired, but would not pick up a second round. At this point I am willing to assume that it is my 1990’s era GI magazines, as they are pretty old and banged up.

My plan is to go get me some new p-mags and try again after working on the gun a little.

Hopefully my next Polymer AR-15 Test Fire will live up to my expectations and I can test the gun until I burn it up.

If I can get 100 rounds out of the gun in a row I will feel like it was a positive test, as some who want an off the books lower would only need it to get a better gun in the event of a total confiscation of weapons. At least that is a thought process of a potential reason to make your own 100% lower.



Okay I bought new magazines, I cleaned up the gun, and I have brand new ammunition.

As you can see from the video it did not go well. After taking the gun back to the shop I found that the pins walked and elongated the hammer pin hole.

Elongated Pin holes can cause the gun will fire more than one round when the trigger is pulled.  As you can imagine that is dangerous if not anticipated.  Additionally, the BATFE has gotten convictions for the possession of an unregistered machine gun.  They have pursued this on occasion knowing that it was the result of an undesired firearm malfunction.

To keep this from happening again I built up one of the other lowers and too my surprise the upper did not fit.

4 out of 5 of my freedom 15 lowers my upper did not bolt on. I could not find an upper to fit them.

The freedom15 company gave me the story that they have loose and tight US Mil-Spec and they make the lower to the tight spec and I needed to find an upper that was made to loose spec.

That sounded like BS, but I asked them if they knew a “loose specification upper” manufacturer. They could not tell me and I could not find any company that advertised such.

The gunsmiths I talked to thought I was an idiot for asking.

Anyway, to try to salvage it I got some anti-walk pins, but even that did not solve the problem on the original lower.

I rule this entire thing a bust. I know that some have had good results with these lowers, but their customer service showed that they are plastic guys not gun guys and they could not answer specific questions about the AR.

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