How to Build a Polymer 80 Pistol

Posted by 80-lower on Jun 24th 2019

How to Build a Polymer 80 Pistol

Polymer 80 pistol builds have become a popular alternative to simply buying a Glock® or pistol at the local gun store. Thanks to its polymer construction, fabricating a Glock frame is pretty easy to do. Just like the 80% lower receiver, these 80% pistol frames have allowed shooters to build virtually every series available at home. Thanks to our friends over at Polymer80, now you can build your own, too! Here's a guide on how to build a  pistol with a Polymer 80 frame.


If you're totally unaware of what we're discussing, here's the quick-n-dirty: You can legally build an unregistered and un-serialized pistol handgun at home, without ever going through an FFL, filling out any paperwork, or paying any extra taxes or fees. The Bureau of Alcohol, Tobacco, and Firearms gives this project a green light. They say you can build a gun at home with no license or FFL if it's for personal use. Check your local and state laws first, though. Some states (like Washington) have banned the practice of building polymer firearms. Other states require that your frame or receiver blank be serialized before it's turned into a firearm. We're not lawyers, so consult with one to make sure this is legal where you live.

Tools You Will Need

Here are the other tools you'll need to get the job done:

  • Hammer
  • Hand drill
  • Bubble level
  • Tabletop vise
  • Roll pin punches
  • Files or sandpaper
  • Drill press, Dremel or snips

Picking a Polymer 80 Pistol Frame

The secret to this project is the Polymer 80 pistol frame. Once you cut and drill your frame, it becomes a firearm by definition. You can then install all the parts you need on that frame, turning it into a pistol handgun that you built yourself. You need to pick the frame for the series you want to build:

Each polymer 80 frame kit includes:

  • 80% pistol jig
  • Polymer 80 pistol frame
  • Locking block rail system
  • Locking block rail pins
  • Trigger housing pins
  • Rear rail module
  • End mill bit
  • Drill bits (M3, M4)

Once you've picked out your kit, it's time to get started with setting up your frame, jig, and tooling. Then we can start machining!

Getting Started

To things keep simple, let's look at the major steps you need to complete on your 80% pistol frame:

  1. Drill the trigger pin hole
  2. Drill the locking block pin hole
  3. Drill the trigger housing pin hole
  4. Cut the slide rails
  5. Cut the barrel block

Step 1: Jig and frame setup

First, you need to set your frame inside the included 80% jig. The jig automatically aligns the frame for cutting and drilling, so no measuring or custom fitting is required.

The jig should completely encase the frame and each half of the jig should sit flush against the other half. The top of the jig is marked with instructions, showing you where you need to remove excess material for the slide rails.

You can remove the excess material on the slide using a drill press and end mill bit, a Dremel, or a simple pair of snips. But before we cut the top of the frame, we're going to complete our drilling steps.

Step 2: Drilling the frame's holes

With the frame seated and the jig flush, you'll need to secure the assembly in a tabletop vise. Once secured, you can drill the trigger, locking block, and trigger pin holes.

Do not use a drill press for this step. The jig and frame shouldn't be gripped by the top and bottom or drilled while it's laying horizontally. This can make the jig flex and mis-align itself.

Instead, make sure your tabletop vise is leveled using a bubble. Secure the frame and jig inside your vise vertically. The vise should grip the bottom half of the jig (circled in green). It should be just snug enough to remain still. Over-tightening will cause flexing.

Each hole is marked with the appropriate drill bit (M3 or M4), noted by the green arrows. Don't attempt to drill completely through the frame on one side. Instead, drill half-way through each side to complete each hole.

Step 3: Cutting the top rails

After drilling your holes, leave your frame and jig secured in your vise vertically. Now you can begin removing the excess polymer on the frame's rails.

The jig is clearly marked, indicating where to remove material. At this point, you have to decide how you'll complete this step: With a drill press, a Dremel, hand files, or a pair of snips. Any method will work just fine, but a Dremel or snips work fastest.

You'll want to remove the excess, raised material so the top of the frame is flush with the top of the jig (pictured with green arrows). Don't cut any part of the jig, including the raised red portions. The jig should never have material removed. Once the excess material is removed, it should be sanded to a smooth finish using sandpaper or hand files.

Step 4: Cutting the barrel block

Some say this is the most difficult step but if you take your time, it's really simple. To cut and shape the barrel block, you'll need a Dremel, hand files, or a drill press.

As pictured, you need to remove the excess material inside the red markings.

Do not remove any of the polymer highlighted in red. 

The part highlighted in red is the slide buffer stop. Removing any of this material will cause your slide and frame to fail to function.

If using hand files or a Dremel, simply keep your frame and jig secured vertically in your vise. Begin slowly sanding and filing down the excess material from the top, until you reach the lip of the slide buffer stop.

If using a drill press, secure your frame and jig in your vise as shown to the left, and use the provided end mill bit to remove the excess polymer. Complete this step by sanding the rough edges of the slide buffer until smooth and round.

With this final machining step completed, you now own a finished pistolframe, a firearm by definition. Now you can start installing your parts!

Polymer 80 Pistol Parts Assembly

First, we have to install the parts that came with our frame - the locking block rail and the rear rail module. The locking block rail can be installed immediately. You'll need a pistol frame parts kit to install the rear rail module.

Step 1: Install the locking block rail

The locking block rail combines both the locking block and slide rails, providing strength behind the slide buffer stop. The locking block rail installs using the provided 3mm x 25mm pins.

To install the rail, simply align it with the frame's pin holes above the trigger guard (pictured).

Using your hammer, gently tap the pin through the frame's pin hole and block rail (indicated by the green arrow). The pin should sit flush in both holes on either side of the frame.

Step 2: Install the magazine catch and catch spring

Like we said, you'll need your pistol parts kit to continue with these installation steps. Before installing the rear rail module, you'll need to install your magazine catch and catch spring. To install it, gently tap the spring into the hole inside the magazine well using your hammer and punches (bottom red circle). The pin will stick up into the magazine catch area by approximately 2mm once installed.

Next, grab your magazine catch. There is a notch/hole on the magazine catch, which will capture the end of the magazine catch spring once it's fully inserted. Begin inserting the catch into the rectangular catch hole on the right side of the frame. As you insert the catch, gently pull the catch spring away using a small screwdriver. This will let the catch squeeze between the spring and the magazine well.

Push the magazine catch all the way through the frame until it's resting flush against the frame inside the mag well. Lastly, gently apply pressure to the catch spring, pushing it to the right. Continue doing so until the spring falls into the notch on the catch itself (top red circle). Your finished installation should look like the illustration to the right.

Step 3: Install the slide lock lever and spring

Next, install the slide locking lever spring and stop. Gen 1 to Gen 4 Glocks® use a flat metal leaf spring (pictured) while Gen 5 Glocks® use a coil spring. Most polymer 80 pistols use a leaf spring/Gen 4 setup, but the PF940SC and PF940CL frames use a coil spring. The coil spring install is illustrated below.

To install the lock lever and spring, first insert the spring in the top of the frame, in the cavity circled in the illustration to the right. Make sure the leaf spring is resting completely in its pocket.Next, grab the slide lock lever and insert it into the frame via the rectangular hole on the left, circled in red as well.

As you push the lock lever into the frame, depress the leaf spring using a small screwdriver or needle-nose pliers.

The lever lock will slide over the spring until the spring pops up into the notch on the bottom of the lever. Make sure the hook, or curved edge atop the lever, is facing rearward.

Coil spring slide lock lever install:


First, install the coil spring as shown, left. Next, depress the spring with a small screwdriver as you press the slide lock into place (right).

Step 4: Install the trigger housing and trigger

Now you can install the rear rail module with the trigger and trigger mechanism housing. First, slide the rear rail module around the trigger mechanism housing. Then, slide the entire unit (including the trigger and trigger bar) into the frame. The holes on the assembly should line up with the remaining holes on the frame - two up front near the trigger, one out back on the grip.

Once the holes on the rail, trigger assembly, and frame are lined up, grab the trigger housing pin (one of the included 3mm x 25mm pins) and gently tap it into the trigger mechanism housing pin hole (not the trigger hole itself) on the grip.

Next, from your parts kit, grab the smaller-diameter locking block pin and install it into the smallest hole near the slide, directly above the trigger pin hole.

You should now have one hole remaining on the frame: The trigger pin hole. Grab your slide release lever (pictured right) and slide it alongside the trigger. Align the hole on the lever with the hole on the trigger, and the trigger pin hole on the frame. With all three holes aligned, tap in the large trigger pin provided in your parts kit. Take your time, being careful not to smash the small spring.

Step 5: Install barrel, slide, and test functionality

Your pistol frame is now completely assembled and ready to accept a barrel, slide, and slide parts kit (recoil spring, operating rod, firing pin, etc). At this point, you can install your slide and its components and test the functionality of your pistol.

Do NOT perform a functions check with a loaded magazine.

The first functions check will likely be tight. Remember, you're the one who set the tolerances for the frame and slide. Some additional sanding and fine-tuning may be required. When you perform your first functions check, apply plenty of lubricant to the slide, frame, and internals. Work the slide a few times back and forth fully to test its feel. Check to make sure everything is functioning correctly:

  • The slide moves back fully without binding
  • The slide slams into battery fully when released
  • Pulling the slide back partially still allows for full battery
  • The magazine catch and release works properly
  • The slide lock works properly

Once you've confirmed all basic functions work, you can test-fire with a loaded magazine. Always shoot in a safe direction with eye and ear protection. Check that the pistol cycles completely from first to last round. If your pistol fails to cycle fully or fails to go into battery after a round has been ejected, additional sanding and fitting may be required. There is a natural break-in period, so don't disassemble your pistol and attack it with files or sandpaper until you've test-fired a few magazines to isolate recurring issues.

If everything works, then you've just finished your first Polymer 80 pistol build and assembly, from scratch.


Install Troubleshooting

Fitting the locking block rail system can be difficult. If you experience issues installing either of these components, troubleshoot with the steps below:

Fitting the locking block rail

If the locking block rail fails to fully seat itself in the frame after you've cut and drilled it, you can gently "spread" the frame apart just slightly to get it seated. You'll need a small cylindrical tool measuring 7/16" in diameter. A wood dowel or tool shaft works just fine for this.

To spread the frame, insert the tool into the trigger opening. With gentle pressure, you can move your tool to the left or right just slightly to spread the frame apart.

With the frame spread slightly, set the front and rear legs of the locking block rail partially into the frame. You can then remove your tool and continue the installation of the block rail with the trigger assembly. Install the trigger assembly first, then push the block rail down completely to seat it.


With this guide, you should have the know-how to build your own polymer 80 pistol with confidence. Have questions about getting started, what tools to use, or something else? Just get in touch with us! We're here to help via phone or email. Now get to building!

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.