Polymer 80 PF940c Custom Build…DIY Glock 19!

How would you like to build your own custom Glock 19?  Well, with a little help from Polymer80 and Brownells, it can be a reality!  The polymer80 PF940c is a Glock 19 sized 80% lower kit.  It contains a jig, finishing bits, parts, pins and the frame of the pistol…80% complete!

This article will walk you through the steps of building your own Polymer80 pistol, with parts from Brownells and a few others.  I have parts links throughout the article, so feel free to click and explore…and if you use the links to purchase your parts, it helps support the Desert Guardian Projects in the future!



Let get started.  The Polymer80 PF940c frame come 80% finished from P80 (hence the 80% lower moniker).  In the box, you will find the frame, jig, front and rear rail modules, pins and 3 drill/mill bits.  Take everything out and familiarize yourself with the kit.  There are many other parts needed to complete the build, but we will cover that shortly. Here we go:


The first time I built an 80% lower, I was shaking in my boots.  What if I mess it up?  What if I’m off by a tiny bit building a firearm?  Well, relax…it’s not as daunting as you are making it out to be.

Lower Parts List:

Here’s what we are using to build this custom Polymer80 Lower.

Polymer80 PF940c Frame Kit.   These are available in a host of colors.  The following link is for the black version.

Brownells Glock 19 Gen 3 Lower Parts Kit.  This includes all of the parts needed to finish the lower.


Optional: Hyve Technologies Trigger and Mag Release.  I like to customize as I go, so I opted for the Hyve gear in this build.  There are many trigger manufacturers out there, so check them out…and triggers can be swapped later.

Tools Needed:

There are several ways to “mill” the frame of a Polymer80 lower.  You can use the included End Mill Bit and a drill press, use a large file, or use a rotary tool, as I have decided to use in this build. In addition to the provided drill bits, here’s what I used for the build:


  1. Rotary Tool (Dremel) with spiral sanding bands.
  2. Hand Drill
  3. Razor knife / Hobby knife
  4. Sandpaper (400/800/2000)
  5. Wheeler Hammer & Punch Set


These are the tools needed for performing the 3 parts of finishing of lower; decking  the top of the slide, milling the guide rod channel, and drilling the pin holes. So let’s get started!

STEP 1: Insert the frame into the provided jig.  It only fits one way, so this should be a simple step.

STEP 2: Grab the rotary tool with a spiral sanding band, and at a MEDUIM speed, start slowly working your way down on the rails.  Let the rotary tool do the work…don’t force it, push hard, or try to go fast.  It doesn’t take long, and slow and steady is the way to go!  The top rail that you are sanding down needs to be flush with the top of the jig.  Be careful not to remove the red material on the jig.  I brought it down about 90% of the way, then removed the frame from the jig and fine-tuned it with the rotary tool.  You can also use a large flat file to finish it as you get close to the line on the jig.  Repeat for all four “rails”, 2 front, 2 rear.  Gently touch up and remove and large burs with a razor or hobby knife.

When you have finished the grind down to the jig line, use sandpaper to smooth it out.  400 to 800 to 2000 works very well to remove any coarse lines or small bits you may have missed.


STEP 3: The guide rod channel has a U-shaped section that needs to be removed.  Using the rotary tool, slowly and gently remove the required material, shifting from front to rear, and gently working the tool into the tight spots.  The material to be removed is evident by a line on the polymer, but you can always refer to the Polymer80 instructions. Use a razor hobby knife to remove any burrs or trim as needed.  REMEMBER…just go slow, and remove a little bit of material at a time.  This is a custom pistol…no need to rush it!

STEP 4: Drilling the pin holes.  DO NOT DRILL YET!  READ THIS SECTION FIRST! With the frame secured in the jig, it is time to drill the pin holes.  There are two provided drill bits, one large, and one small.  They are used in the corresponding large and small holes. Pretty simple, right?  DO NOT DRILL ALL THE WAY THROUGH THE JIG.  Using your hand drill, gently drill the holes from one side, then the other, keeping the drill straight and true. Use the large bit for the large hole, and the small bit for the small holes.

STEP 5: Finish up.  Using your hobby knife, gently trim any burrs and clean out any excess plastic pieces.  Check the top rail line and touch up with sand paper as needed.

You are now ready to start the assembly process!!

Let’s take a look at the parts.

The Polymer80 kit includes:

  1. Front rail module / locking block
  2. Rear Rail Module
  3. 2 rail system pins

The Brownells Lower Parts Kits includes:

  1. Magazine Catch Spring
  2. Extended Magazine Release
  3. Trigger Housing Pin
  4. Locking Block Pin
  5. Slide Lock
  6. Slide Lock Spring
  7. Extended Slide Stop Lever with Spring
  8. Trigger Housing with Ejector
  9. 5lb Connector
  10. Trigger Spring
  11. Trigger with Trigger Bar
  12. Trigger Pin


First, I like to test fit the P80 rail modules into the finished slide.  The rear module drops right in, and the front locking block module slides in, starting with the rear “legs” and tilting the front in. After test fitting, remove the modules and set aside.


Step 1: Slide Lock

Insert the slide lock spring into the frame.  The little “L” shaped tab goes down and towards the front of the frame. Sometimes using a pick or small screwdriver to move it into place makes it a little easier.  Then, insert the slide lock into the frame from either side…be sure the “hump” is UP, and the ridge on the hump facing the rear of the frame. Use a small screwdriver or pick to depress the spring as you slide the slide lock into place.

Step 2: Mag Release

Insert the Mag Release spring into the grip of the frame.  The mag release spring is a thin metal rod. Looking down from the top, drop the spring into the “V” shaped notch in the front of the inside of the grip. Snug it down gently with a dull tool or punch.  Next, slide the mag release into the frame from the right side toward the left, and be sure it slides in between the spring and the front wall of the grip. When it is in place, use a pick or small screwdriver to push the spring into the notch on the mag release, and it should snap into place.


Step 3: Trigger Assembly

Locate the trigger spring, trigger, connector and trigger housing.  Insert the connector into the slot on the right side of the trigger housing.  Then, take the trigger spring and install it onto the back of the trigger housing into the little hole.  With the trigger spring in you left hand, looking at the right side of the housing, the trigger spring should install with the open end of the spring facing down, then you will rotate it up, and install the other end of the spring into the hole on the trigger bar, with that open end of the trigger spring facing down also. The trigger bar will then twist gently into place, and you have a completed trigger assembly.


Step 4: Install the rear rail module and trigger assembly.

Insert the rear rail module, and then drop in the trigger assembly. Angle it a little towards the front of the frame, and slide the trigger into its hole, and the trigger housing into the rear module. This should drop right in! Insert the rear pin.

Step 5: Install the front rail module / locking block.

Insert the front rail module into the frame, and insert the front pin. Next, insert the locking block pin (top pin) BEFORE installing the slide release.


Step 6: Install the slide release and trigger pin:

After the locking block pin is installed, it will hold the small spring attached to the slide release in place.  Insert the slide release into place, sliding the loop end into the little slot next to the trigger.  Starting from the right side, slide the large trigger pin about halfway in so it is through the slide wall, locking block and into the trigger.  Then, pull the slide release up slightly and give it a wiggle, and gently push the trigger pin in the rest of the way.  Jiggling the slide release allows the pin to ease in and self-locate its way.


You now have an assembled Polymer80 PF940c lower! Congratulations! Using your punch or Glock armorer’s tool, center the pins as needed and we will move on to the slide assembly!




Next up, I will walk you thought the process of building the Brownells slide!  Here’s what you will need:


Tools Needed:

  1. Wheeler Hammer & Punch Set
  2. Brownells Channel Liner Tool
  3. Sight Pusher (Optional)


Brownells Iron Sight Front Serration Slide:


Brownells Glock 19 Slide Completion Kit:


Backup Tactical Stainless Threaded Barrel.




TruGlo Tritium Fiber Optic Sights.




In addition to the bare slide and barrel, the Brownells kit includes:


  1. Extractor with loaded chamber indicator (LCI)
  2. Extractor depressor plunger & spring
  3. Spring loaded bearing LCI
  4. Firing pin
  5. Firing pin safety & spring
  6. Firing pin channel liner
  7. Firing pin spring cups
  8. Firing pin spacer sleeve
  9. Slide cover plate
  10. Recoil spring assembly

Step 1: Install the sights.

Installing sights is a lot easier with a sight centering tool, but I used a brass punch and it worked out great. The rear sights on a Glock should always be installed from left to right, in accordance with a slight taper in the slide slot.  The TruGlo TFO sights have a small set screw, so be sure to back that out a bit before installing.  Then, wipe any oil or dirt out of the rear slot and slide the rear sight in from the left.  It should go in about half way.  Next, gently tap it to center with a mallet and punch, tap gently and slowly center the rear sight.  When centered, tighten the set screw.  The front sight drops into the hole on top of the slide, and a screw holds it in place from underneath.  Be sure to clean the area, then install using red loc-tite to hold it in place. Use a front sight tool and tighten it up.

Step 2:  Striker / Firing Pin Assembly

Locate the firing pin, two firing pin cups, firing pin spring, and firing pin space sleeve. Insert the firing pin into the spacer sleeve with the firing pin tail sitting in the notch of the sleeve.  Next, slide the firing pin spring over the pin, and depress the spring to install the two firing pin cups. It seems so easy, but I have sent cups flying across the workshop many times, so be patient. Once cups are installed, the assembly is complete and you can set it aside.


Step 3: Channel Liner Installation

Bare slide do not come with a cannel liner installed, so it must be installed before final assembly.  Using the Brownells Channel Liner installation tool, install the channel liner into the striker tube on the slide, and tap in place gently with a small hammer. Sorry, I don’t have a picture of this process.


Step 4: Plunger Assembly

Locate the extractor plunger, spring and spring loaded bearing. Snap the spring onto the end of the bearing and plunger and set aside.


Step 5: Install the Extractor

Drop the LCI Extractor into the slot on the right side of the slide, and hold with your thumb as you install the firing pin safety and spring form the underside of the slide.  These will hold each other in place.


Step 6: Install Plunger, Striker assembly and back plate.

Drop the striker assembly into the striker hole, than the plunger into the smaller hole on the back of the slide.  Next, press the striker assembly in as you slid the back plate on about half way. Then, using a small punch or tool, depress the plunger assembly in and slide the back plate all the way into place.  It should snap in place.


Step 7: Barrel and Recoil Assembly

Finally, slide the barrel into place and insert the recoil spring assembly. Your slide is now complete!



Ok, you have now finished the 80% lower, and assembled the slide!  Following the recommended Glock lubrication steps, lube it up and gently slide the slide onto the frame for test fitment.  Once the slide is on, lubed and moving freely…get that beauty out to the range!!  Be safe and have fun!

Desert Guardian…OUT!



Note:  Please check your state and local laws regarding the serialization of your new pistol and regulations for carry. In my state, I have local shops that can serialize the completed pistol for legal carry. This will vary from state to state, even though the 80% lowers are 50 state legal.  This blog entry is for instructional purposes only, Desert Guardian, all employees, affiliates and holdings are not responsible for improper use of tools, gear or firearms.

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