80 Percent Arms GST-9

Build A Pistol At Home!
; .

Home brew: Tom built this high-quality 9mm pistol in his garage
using common tools and parts supplied by 80 Percent Arms.

No, this isn’t a Gary Smalley or Tony Robbins pep talk. I’m talking about building your own pistol at home. In most states, it’s perfectly legal to build your own firearm for personal use, provided you’re legally eligible to own a gun and don’t plan to sell it.

While I might endeavor to construct one from rocks and deadfall, I figured I’d make use of modern technology and entrepreneurial creativity so I talked to the folks at 80 Percent Arms. As the name implies, they’re in the business of selling “not quite firearms.” These 80% blanks are partially finished gun components. In the case of their GLOCK-compatible pistol kits, it means the frame as it is the normally serialized part defining a legal firearm. For rifles, it’s the lower receiver. The idea is simple. You receive a hunk of polymer in the mail that looks like a pistol frame, but cannot be assembled into a pistol until you complete the manufacturing process.

When I want to impress my shooting buddies, I describe how you have to “mill the frame” yourself to complete the 80% blank. Between you and me, it’s not really “milling” but drilling, shaping and a bit of sanding. This frame is polymer after all, so no CNC machines or cutting oil are required for this project. If it makes you feel better, you can use the Dremel tool gunsmiths warn you to keep far from your guns. You’re welcome.
Mailbox Nirvana


The frame mounted in the jig assembly. The jig is required to place pin
holes but is handy for removing the excess polymer from the frame too.

Mailbox Nirvana

Since we’re not talking about actual firearms, you can get all this gear shipped straight to your home. Mine ended up in the mailbox by the street along with the bills and a Bed, Bath and Beyond sale flyer.

You’ll need to order two items to make your own pistol: the frame kit and a jig kit. The frame comes with the polymer blank and separate magazine extensions for 15- or 17-round configurations. If you like, you can order parts like barrel, slide, trigger components, etc. at the same time or you can supply your own. If you’ve ever wanted to assemble a premium pistol using hand-picked aftermarket components, this is the way to go. All of this is available via regular mail direct-shipped to your home since they’re just parts.

For this build, I went whole hog and ordered the 80 Percent Arms GST-9 Pistol kit. It comes with everything you’ll need including the frame, magazine extensions, trigger kit, slide lock hardware, barrel, recoil spring assembly and slide. It’s all there except the pins and rail blocks which are included with the GST-9 jig kit. I should note the GST-9 is no bare-bones pistol. The slide is serrated, scalloped on top, and features cutouts that lighten weight and make it look, well, awesome. The slide is also cut for optics and features a set of GLOCK-style front and rear sights if you want to stick with “irons.” I was pleasantly surprised, and impressed with the sexiness of the GST-9 components.

This package also includes the pins for internal parts and the all-important rail blocks, front and rear. This dual packaging is likely done to ensure no one is shipping firearms around illegally, even though nothing included is a firearm in a legal sense.

The jig kit contains a frame to assist in perfect placement of holes you’ll drill and the polymer you’ll remove.


Tom used his new drill press, well, because it was a new toy. Thanks to
the protruding drill guides, you can get equally good results with a hand drill.

The jig comes with drill and cutting bits, pins and the frame rails (not shown.)

Tom used wire cutters to remove most of the material
before shifting to the included cutting bit.

Milling Made Easy

There are three operations you must do to the blank to make it complete and ready for assembly: “mill” the excess polymer from the dust cover area under the future muzzle, cut and sand excess polymer from the top of the frame and drill all the required holes in the frame.

I chose to leverage all the help I could get and use the jig for everything. Starting with the holes, I used the included drill bits and my tabletop drill press to bore out trigger and trigger-assembly-housing holes in the frame. The jig assists in drilling a perfectly straight and vertical hole, but I was itching to use my press, so I did it. You can just as easily use a hand drill with perfect results. You’ll get two sizes of bits and the jig is clearly marked so you drill the right size holes in the right places. You cannot mess this up!

Next, I had to remove excess polymer from the muzzle area and in two areas on top of each side of the frame. To reduce the “milling” required with the included cutting bit you can use on a Dremel tool, cordless drill or screwdriver, I snipped excess plastic away first using wire and end cutters. I trimmed the top-of-frame tabs almost flush and cut a “V” in the semi-circular block in the muzzle area which left relatively little material to grind away. Using the included bit on my Dremel tool, I took everything down to the level required. Last, I used wet fine-grit sandpaper and a felt polishing wheel on the Dremel to smooth things out.

At this point, you’ve made, in terms of the law, a firearm. Even though it’s a piece of plastic, it can be readily assembled into a pistol so treat it as such. Don’t sell it, and if you’ve robbed a bank or committed another felony, you can’t possess it.


Removing the polymer plug from the muzzle area. The job took
just a couple of minutes. Tom found it idiot-proof.

Besides a drill to build the frame, all you’ll need is a hammer and punch to complete assembly.


If you buy the full GST-9 kit, you’ll need nothing but either a 15- or 17-round magazine, depending on which grip module you install. Or, since they’re easy to swap, how about both? If you build your own from chosen parts, be sure to order GLOCK Gen 3-compatible components. The GST-9 frame works with Gen 1 through 3 extras.

Rather than go through the entire assembly process here (it’s standard for GLOCK-compatible pistols), you can see exactly how it’s done on our YouTube channel (FMGPubs). For now, know you’re looking at just a couple of minutes work to drop in a trigger assembly, install the slide lock, slide-stop, magazine release and rails. That’s it. The only tool required for parts assembly is a punch to set the pins. It’s also handy for holding slide stop and magazine catch springs while you install those parts.


A few quick and dirty 10-yard break-in groups before formal accuracy
testing showed the pistol shot just fine from the first shot.

Does it Shoot?

While I was confident the GST-9 was safe, I had no idea what to expect with handling and accuracy. The pistol is very light thanks to the generous slide cutouts and would make an excellent carry gun. Regardless, recoil was soft and easily absorbed by the polymer frame. Taking full advantage of the built-in optics cut in the GST-9 slide, I mounted a Trijicon SRO red dot sight. The combination was butter — a smooth handling pistol facilitating fast hits on target.

I tested four varieties of Federal ammo with the GST-9: Syntech Defense 138-grain, Syntech Action Pistol 150-grain, Punch Self-Defense 124-grain and NATO 124-grain. The results from some quick 20-yard, five-shot group accuracy testing? Stunning. In the order above, I measured groups of 1.36″, 1.46″, 1.6″ and 1.42″. Remember, I built this frame in my garage! This is a testament to the quality and consistency of the jig setup to some degree, but primarily a huge validation of 80 Percent Arms’ barrel and slide assemblies.

Consider me impressed! If I can do this and achieve outstanding results, you can too!



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