How To Build a Glock From an 80 Percent Frame

I like to build my own guns. Using skills acquired in military and civilian schools, I began building 1911s from bare frames three decades ago. Eventually, I was assembling AR-15s, M14s and M1 Garands. An inventory of my safes would reveal maybe 50% of my firearms were assembled in a factory. A few were built on incomplete, or 80% receivers. I suppose everyone with a shred of creativity in their body needs an outlet for it. Building guns is mine.

If you wish to assemble firearms from 80% receivers, there are legalities to keep in mind. You can build as many as you desire for your personal use. Federal law does not prohibit it. But, you can’t sell them to other parties without a federal manufacturer’s license from the ATF and payment of excise taxes. They are yours forever. The firearm you build must also comply with state and local laws. The above also applies to building guns with completed receivers which already have a manufacturer’s marking and serial numbers—yes, the receiver is the restricted part but it’s not a handgun or rifle until it is assembled as such.

Gun banners refer to weapons assembled on 80% frames as “ghost guns,” since they lack serial numbers and whine about how they are “untraceable” by law enforcement. This is a bogus argument. In most jurisdictions, firearms aren’t registered to individuals, and once they are sold by the original owner, the ATF can’t trace them anyway from a central database unless registration is part of state law. Felons are already breaking the law if they possess a firearm. Laws only affect law-abiding individuals.

Last year, I wrote about 80% AR-15 receivers and how to finish them. At the same time, I was eyeing ads for 80% Glock frames and keeping the idea on the shelf for when my editor would ask me what projects I had in mind for upcoming articles. A voice inside my head was saying “you need to try this.”

Disclaimer: I am not a Glock fanboy. I respect the design for its reliability and simplicity, and I have owned a pile of them. As a gunsmith, I have repaired, modified and inspected them. Unfortunately, I was blessed with relatively small hands, and the Glock grip simply doesn’t fit me very well. I also think the grip angle is weird, but I’m an old guy, and my background is 1911s, so if I have a choice, I shoot what I’m most comfortable with. That being said, if Evil is coming and all I have is a Glock 19, I would feel very well-armed.

Before we begin building Glocks, a few words about the fascinating rise of Gaston Glock and his pistol are in order. In the early 1980s, Glock ran a small Austrian firm that manufactured household items for the civilian market and knives for the Austrian Ministry of Defense. Austria was looking for a new military pistol to replace its aging fleet of P38s. A domestic product was desired. Enter Gaston Glock, a man experienced in manufacturing things other than firearms. Determined to win the contract, Mr. Glock hired experts, studied the problem carefully and produced a high-capacity pistol with a polymer frame that became the standard sidearm of police and military units around the world in less than a couple decades. The Glock pistol was designed with modern manufacturing methods in mind (read, CNC) and could be quickly produced in vast quantities with no hand fitting and a high profit margin.

A typical pistol in 1980 had a metal frame (steel or aluminum) and a swinging hammer. Thirty-eight years later, polymer-framed striker-fired pistols are considered state-of-the-art, and the guns that Neanderthals like myself hold dear are becoming historical artifacts. Show up at the range with a Browning Hi-Power, and the kids down the firing line are snickering, “Hey, look at Gramps over there with the Browning.” Heaven forbid you show up with a revolver… The effect of Glock on the firearms industry as a whole cannot be overestimated. An interesting book on this subject is GLOCK: THE RISE OF AMERICA’S GUN, by Paul M. Barrett.

Frames: Choosing an 80% Glock frame to build is easy. As of this writing, Polymer80 (www.polymer80.com) is the only manufacturer of 80% Glock frames I could find. From there, you have a choice of the standard-size PF940V2 frame (Glock 17, 22) or the compact PF940C1 version (Glock 19, 23). I picked up several frames to sample what was available. P80 frames marketed by vendors such as Brownell’s (www.brownells.com) and Lone Wolf Distributors (www.lonewolfdist.com) may vary in grip texture, but are otherwise standard P80 products. Colors available include black, gray, FDE and green.

Polymer80, Inc. was formed in 2013, by David L. Borges and Loran Kelly to manufacture 80% AR-15 receivers, which we reviewed in Firearms News Aug. 2017, Issue 18. .308 AR frames are also available.

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As I mentioned above, there are old codgers like myself who find the grip angle of the Glock distasteful. The problem seems to be the hump at the rear of the grip, forcing the muzzle high when the gun is punched out in a firing stance. Polymer80 has produced its frames without the rear hump in a configuration similar to a 1911, with a straight mainspring housing, although the front-to-rear depth of the P80 frame is still a longer reach than a 1911. I’ve always been curious why Glock (and P80) left the hollow cavity behind the magazine, when eliminating it would make the grip smaller.

Polymer80 supplies its frames in kit form with a plastic jig to hold it in a vise, drill bits, an end mill, stainless steel front locking block/rail module, and a rear rail module and pins. Retail price is $160, but discounts can be found at web sites we all frequent. The frame as provided in the kit is not a firearm, so it may be delivered to a consumer directly without the intervention of a licensed dealer.

Instructions are not provided in the box, but downloadable pdfs and video links are available on the Polymer80 web site. If you have been considering an 80% firearm, building a Glock is the simplest to complete, requiring no skills other than the ability to follow instructions.

The Polymer80 frame accepts Glock Gen 3 parts, so if you are purchasing a slide assembly, keep that in mind.

OK, let’s cut some plastic. I recommend studying the print and video instructions provided on the Polymer80 web site before permanently altering the frame. The pdf is EXCELLENT and very easy to understand. We will cover two methods of finishing the frame: with a drill press or mill and without machine tools. The frame kit includes a 9mm end mill, which will be held by your drill press chuck or mill collet. Why 9mm? Polymer80 uses the same cutter for its AR-15 and AR-10 lowers, so they decided to standardize that size for all its products.

If you are using a mill/drill like I am to demo this article, the odds are you don’t have a 9mm collet. A Jacobs chuck will work or a 9mm collet can be purchased from MSC (www.mscdirect.com part number 56448954). A drill press will require a cross slide-type vise, such as the Grizzly Industrial D4082 (www.grizzly.com).

Finishing the frame consists of three steps:

1. Milling off the rails.
2. Clearing the spring tunnel.
3. Drilling the pin holes.

Rails: Lock the 80% frame in the red clamshell milling jig and clamp it in your mill or drill-press vise. My 5" Grizzly mill vise is relatively shallow, so I clamped the jig between two pieces of wood to stabilize it.

Mill off the plastic ribs above the rails at the front and rear locations until they are flush. Finish with sandpaper if you want to be fussy. If these areas are too high, the locking block rail module may not seat correctly, and you won’t be able to install the pins. The red fixture tells you where to cut. Basically, if you start cutting into the fixture, stop there.

If you lack a mill/drill or drill press, the rails can be filed flush with a flat, coarse file. Clamp the fixture in a bench vise and go for it. I finished a frame with only files, and it took a little longer than milling, but the end result was the same.

Spring tunnel: A plastic membrane blocks the passageway in front of the forward rails, where the recoil spring lives. This must be milled and/or filed away within the visible line molded into the plastic. The plastic (ok, polymer) upright surfaces in front of the rails act as a slide buffer and should not be removed, or the slide may strike the rails. Only remove the plastic inside the scribe line. Polymer80 recommends mounting the fixture vertically in the vise and side milling with the end mill. I like to clamp the fixture horizontally and use a ball end mill.

An alternative method would be simply to file out the material or to grind it away with a Dremel. There has to be enough clearance for the recoil spring assembly. Once the front rail section is inserted in the frame, check for any excess material that might rub on the spring. The edges can be trimmed flush to the metal rail section with an X-ACTO knife or utility knife blade.

Drilling: Two drills are provided with the frame kit, 3mm and 4mm. Clamp the fixture in a bench vise. Polymer80 warns against clamping it so tight that the fixture bends and misaligns the holes slightly. The three pin holes that must be drilled are clearly marked to indicate drill size and location. Drill the holes with a hand-held portable drill, using the fixture as a guide. The temptation is to drill the holes all the way through the frame, but the instructions expressly warn against it. Drill the hole half-way through, flip the fixture around, and drill the other side. Pay attention to drill size. You don’t want to drill the 3mm holes with a 4mm drill, or the frame is ruined. Note that there is already a hole in the frame for the forward rail section pin. This pin is not present in factory Glocks, because their rail sections are molded permanently into the frame.

Frame assembly: The frame can be completed with a frame completion kit from Brownell’s. OEM Glock 9mm kits are available for full size (100-023-595) and compact (100-024-280) frames, and .40 S&W parts are also available. Lone Wolf/Polymer80 sells completion kits under its own brand for full size (100-023-998) and compact (100-023-997). The only problem encountered with aftermarket parts was one connector that simply didn’t function correctly. I replaced it with a Glock OEM connector, and we were good.

The frame assembly process started with the mag catch. The Poly80 mag catch was the extended variety, which I don’t really prefer, but I used it. Next up was the slide lock spring and slide lock. The lip on the slide lock should face to the rear of the frame.

The front rail assembly (referred to as the Locking Block Rail System) is inserted into the frame. Getting it started into its slots can be frustrating due to a tight fit. Poly80 suggests spreading the frame slightly with a rod to start it. I used an aluminum rod I had on the bench, while holding the frame in a padded vise by the trigger guard. Prying the frame apart just in front of the trigger was all that was needed to start the LBRS into its slots. Leave it partially installed until the trigger is in place. Next, the rear rail section should slide into the frame easily. Install the trigger mechanism housing with trigger and trigger bar as an assembly. Install the front and rear pins supplied in the frame kit.

Install the rear LBRS pin. Position the slide stop lever on the frame so the hole lines up with the hole in the locking block and trigger, and drive the trigger pin home. Sometimes this last 4mm pin can be tight. Install the slide assembly and perform a quick function check. Verify the slide moves through its full travel and the striker cocks. Dry fire the pistol to make sure the trigger works. Install an EMPTY magazine and retract the slide to ensure it locks to the rear. Check the slide lock to make sure it won’t pull down when the slide is fully forward.

Slide options: The frames I assembled for this article will be 9mm pistols, so my slide options for the full-size frame will be Glock 17, 34 or 17L. The compact frame will get a Glock 19 slide. Complete Glock slide assemblies can be found on internet auction sites. They are not cheap. You will probably not save much, if any, money building a Glock from parts, as opposed to just buying a factory pistol. That said, there are custom slide options.

Intrigued by the boom in optically sighted pistols, I purchased a slide from Brownell’s (078-200-001), modified to accept a Trijicon RMR red-dot sight. The RMR fits on to two raised studs on the slide and is secured by two 4-40 flat-head cap screws. This is a secure mount. I have seen other slides with just two tapped holes in them, but Brownells goes one step further by adding tapered studs. I lost one screw during test firing, but the studs kept the RMR in place.

Admittedly, I’m not a huge fan of reflex-type sights, but if you are, the Brownells slide is a good option. Although the RMR only weighs about one ounce, the slide is lightened somewhat to compensate for the optic, with a slot or “window” cut into it behind the front sight. Material was also removed when the slot was cut to create an optic mounting interface. The addition of iron sights to an optics slide requires they be suppressor-height, and I chose a set of plain black sights from 10-8 Performance (10-8performance.com). A front sight height of .315" allowed the pistol to zero perfectly at seven yards.

Conventional iron-sighted slides in G17/22 and G19/23 lengths are available from Brownells at very reasonable prices, but they were sold out at the time I wrote this article, so I installed a Glock 19 top end on the compact PF940C frame. This made for a light, accurate carry gun, and the improved geometry of the Poly80 grip frame (in my opinion) allowed me to manipulate it easily.

I finished a second PF940V2 full-size frame (ok, I admit I was having fun at this point) and topped it with a Glock 17L slide assembly. Sight radius is your friend and this six-inch slide has it in spades. Apparently, Glock 17L slide assemblies must be manufactured from depleted uranium or some such expensive material, because the price of the complete upper is higher than a new standard pistol. No bargains here.

The question of sights for the 17L slide caused me to pause and study options. The Glock aftermarket contains dozens of sight choices. All I needed were a good plain, black rear and super visible, fiber optic front. As is my usual practice, I found myself checking the Novak web site (www.novaksights.com). I have used Novak sights for most of my gunsmithing career and continue to do so.

A familiar wedge-shaped Novak rear sight was installed on the 17L slide with a MGW 309S sight pusher. If you are changing sights on pistols today, such as Glocks, M&Ps, Berettas, etc., you need sight pusher tools. They may not be cheap, but they are indispensable. One note of caution: if the sight is too tight to install working the pusher manually, STOP and fit the sight. Forcing it further by adding an extension to the pusher handle may damage the pusher and even crack the slide (ask me how I know). A Novak green fiber optic front sight was installed with the standard hex head screw.

Triggers? Well, some people may find the average Glock trigger ok. I find them hideous. Apex Tactical, known for curing Crappy Trigger Syndrome, offers its Action Enhancement Kit for Glocks (Brownells 100-020-706), which includes an aluminum flat-faced trigger in your choice of several colors, a connector and a highly polished firing-pin safety. The result is a lighter trigger with shorter reset and better overall feel.

One last option worth mentioning is a .22 conversion kit. I tested a TSG-22 from Tactical Solutions (tacticalsol.com), which replaced the slide and magazine of the compact frame (PF940C1) and converted it into a .22 caliber Glock 19. A great training aid, the conversion requires high-velocity ammo to function properly. An old box of Remington Viper ammo cycled through it without a problem. The 10-round magazine is standard, rather than compact length. The slide assembly was extremely well-made and looked exactly like a standard Glock slide when mounted.

What’s our next 80% build? Stay tuned. I’ve got some ideas...