The World’s First Truly Modular 80% Glock: The GST-9 By 80 Percent Arms

The frame that I received is a pre-production model, so it does not have a stippled grip: all production models will be stippled. I outfitted my GST-9 with a bunch of aftermarket parts in order to build the gun of my dreams. Most noticeably, I chose to use Rival Arms’ slide, barrel and Tritium MOS height sights, add a HOLOSUN HS507C-V2 reflex sight, and attach Rebel Silencers SOS-450 suppressor.

What’s better than a Glock 19 or a Glock 17? How about a handgun that can be configured to both, and everything in-between! The GST-9 is a 1-3 generation compatible, modular 80% Glock Frame that is currently available for pre-order from 80 Percent Arms. By removing two pins in the grip, you can swap the grip extension for a short or tall grip extension that matches the length of a Glock 19 and Glock 17 grip respectively. This simple, yet ingenious design provides you with the options of a Glock 19, 19X, 19L and 17 (with the 17 requiring a Glock 17 slide and barrel). And, of course, because it is not a firearm from the factory, it can be shipped to your door and requires no registration in most states.

What Makes the GST-9 Different?

As mentioned, the GST-9 is a modular frame that accepts two different grip extensions. One is shorter, resulting in a grip the same length as a Glock 19. The other is longer, configuring the grip to the same length as a Glock 17. Naturally, magazine compatibility changes when you swap these grips out. When in Glock 19 configuration, you can run Glock 19 magazines and larger. Ditto for the Glock 17 configuration of course.

With the large grip extension, this handgun features a G17 length grip, and G19 length slide; configuring it to be a G19X.
Here, the large grip extension has been switched with the short one; making this handgun the size of a G19.

This modular aspect is not the only distinguishing characteristic of the GST-9, as a lot of engineering has gone into this project. This build also features a unique mating interface between the frame and the slide due to the frame rails being extended three times longer than their normal length. This one detail alone creates a more controllable recoil impulse, better repeatability, and greater accuracy. 80 Percent Arms even went so far as to nickel plate these rails which results in reduced friction and increased longevity of the firearm. You won’t have to worry about rust, dirt or grime locking your slide up, even when liquid lubricants on the rails have long since been cooked off.

The GST-9 frame accepts any Gen 1-3 Glock 19 components, accessories, and holsters. This makes the GST-9 the first and only 80% lower that fits in standard Glock holsters. Because you can use any 1-3 Gen parts, you can build up the frame with the exact mix and match of components that you want. Other notable features of the GST-9 frame include the full Picatinny rail for an array of attachments, an undercut trigger guard and a high beavertail, scalloped mag release, no finger grooves, and gas pedals. All of these features equate to a firearm that is more ergonomic, flatter shooting, and consequently more fun to shoot.

Notice the longer frame rails, gas pedal, and textured trigger guard.

If these features don’t quite pique your interest, 80 Percent Arms are sure to capture it eventually as they release more grip modules for the GST-9. There will be more grip modules coming in the future, like competition magwell, different contours for different ergonomics, etc.

When/Where Can I Buy One?

You can currently get 30% off MSRP by preordering a GST-9 frame, or full build kit on 80 Percent Arms’ website. As suggested, you will be able to purchase either the frame and jig (sold as separate items for legal reasons) or the full kit which includes everything that you need for a functioning gun. Prices range from $79.99 – $699.99 currently but will go up as soon as they start shipping in the spring of 2020 the pre-order sale ends.

There are only a couple of unique aspects to my build when compared to 80 Percent Arms’ complete build kit. For starters, I have a threaded barrel, tritium MOS height sights and a slick nitride coating on the barrel. For about $400 less, you can preorder the GST-9 complete build kit and get a high-quality “Gucci” gun that only differs in these areas.

For my build, I chose to use A Rival Arms Slide and Tritium MOS height iron sights accompanied by a HOLOSUN HS507C-V2

Doing the Other 20% (AKA Building)

Now for the fun part: finishing the 80% lower to turn it into a firearm. This is the first 80% lower that I have started and completed on my own. In the end, I proved that if I can do it, anyone can. We have full guides published on GunsAmerica on how to complete 80% Glock builds in detail, so I’ll skim over the process here:

These are the parts that will make up my completed firearm.

Starting at the beginning: before I began the modifications to the lower, I noticed a few things. The jig that you get from 80 Percent Arms is extremely robust, being constructed of glass-filled polymer, it is 3x stronger than other jigs on the market. It also has deeper drilling guides, helping you drill perpendicular to the workpiece. And once I had all five bolts tightened down in the jig, it was locked down extremely tight, resulting in exact and precise modifications.

The GST-9 Frame goes into the jig. Then you bolt it shut and begin to work.

One other note: The jig comes with all of the required tooling for completing the lower.

The First thing that I set out to do was to drill the appropriate holes through the frame. You cannot mistakenly drill the incorrect hole, because the drill guides are the exact size of the bit that you need to use. I chose to use a cordless drill for this task and I knew that I could potentially skew a hole. I mitigated this by drilling halfway through one side, flipping the jig over, and finishing the hole from the other side. In the end, this method worked out great.

The beefed-up drill guides really helped keep everything square.

Next up, I removed the excess material from the top of the frame with a Dremel and the provided bit. I cut this material down until it was almost flush with the frame and then switched to a flat file wrapped in 220 grit sandpaper. I did this in order to grind these tabs down square to the frame without removing excess material. The last step was to remove the material in the barrel channel, which I also did with a Dremel and sandpaper.

Dremeling down the tabs takes very little effort. Be careful to not over-cut and eat into the jig.

Once this was done, I removed the bolts from the jig, dropped the lower out, and I was ready to start installing parts. This whole process took me approximately 10 minutes which I would say is a long time because I was taking extra care to make everything perfect and pretty.

Filing the tabs down the last little bit, keeping everything square.

Once the lower had been modified, I watched a couple of videos online on how to assemble the remaining parts and then dove into that aspect. I installed OEM Glock 19 internals and a Rival Arms RMR cut G19 slide, threaded barrel, and night-sights with an accompanying HOLOSUN HS507C-V2 reflex sight. Completing the lower proved extremely easy, as the steel rails for the GST-9 dropped right into place and all of the pins lined up just perfectly. Once the lower was completed, the slide racked right into place. With that, my build went from a hunk of plastic to a completed firearm in under an hour.

Once the tabs are ground down, holes are drilled and the front barrel channel is cleared, this is what you end up with before installing the frame rails and internals.

Components Used in My Build:

  • 80 Percent Arms GST-9 Frame $79.99
  • 80 Percent Arms GST-9 jig w/ toolkit & slide rails $ 19.99
  • OEM Gen 3 Glock lower parts kit $43.99
  • OEM Gen 3 Glock slide parts kit $79.99
  • Rival Arms Glock 19 RMR cut slide $470.99
  • Rival Arms Glock 19 3rd & 4th Gen threaded barrel $235.99
  • Rival Arms Glock 17/19 Tritium night sight MOS height $105.99
  • HOLOSUN HS507C-V2 reflex sight $309.99
  • Total cost: $1036.93 (without optic)
At this point, I had just installed the frame rails and internal components. Next up, to assemble the Rival Arms slide.

Putting the GST-9 Up To The Test

The lower that I received is a pre-production model, so it lacks stippling on the grip and was 3d-printed instead of injection molded. You’ll probably notice that in the pictures. Once my GST-9 was built, I still wanted to put it through the same tests that I would put a finalized model through in order to give you all a point of reference.

The first thing that I did once I had the handgun setup in my preferred configuration (Glock 19X), was to slap a suppressor on it and run a bunch of ammunition through it. Admittedly, I had a few hiccups, but they were quickly solved by switching from ammunition that I had reloaded specifically for a different 9mm to factory offerings. The problem that I saw was hallmarked by the slide hanging up slightly out of battery. But as I said, this stopped happening the instant I fed the handgun factory ammo.

I continued to run hundreds and hundreds of rounds (subsonic and supersonic) through this custom build without any further failures. While using it, I noticed that the GST-9 was extremely comfortable in my hands. I especially liked the gas pedals built into the front of the frame. These were just the right amount of low profile and tactile. Applying downward pressure made shooting the GST-9 extremely flat and quick for follow-up shots.

Notice how much real-estate there is on the molded-in gas pedals. Excuse the dirty barrel hood, I had just finished putting a few boxes of ammunition through my GST-9 build, suppressed.

Once the GST-9 had gained my confidence, I began to carry it while I was out hunting. I think of this as the ultimate test because the firearm has to endure adverse weather conditions, dirt and grime, and extreme temperatures; all the while it is paramount that the GST-9 functions through all of this. I’m happy to say that it never missed a beat, and I just gained more trust in the firearm. Now, I would not even hesitate to carry it for personal defense.

I enjoyed carrying the GST-9 while hunting, and it never let me down out in the field.

Accuracy Testing

I realize that most of the accuracy of a handgun is derived from the slide/barrel quality, but I am sure that you all will want to know how this GST-9 build performs. I tested 5 different ammunitions across a weight range of 108 grains to 147 grains. Each functions reliably in this build, but some shot better than others. The distance I was shooting was 25 yards, and I wound up shooting unsupported because I forgot my sandbags at home. That said, keep in mind that my own error is undoubtedly being displayed in each group.

This is a 4 shot group because I ran out of ammunition during my test. This Norma MHP shot better than all of the other ammunition I tested, so I am sure that it would be similar with one more bullet stacked in there.
This Blazer Brass 115 grain shot just as well as the rest of the ammunition I tested, which is good because it is very affordable to spend a day at the range with.

The Legality of 80% Firearms

Just because I know that I will see this topic in the comments, I want to quickly touch on the legality of 80% firearms. I do not know all the laws in each individual state, so check your local laws before ever doing anything like this: but to my knowledge, 80% firearms are legal in most states besides California, Connecticut, New York, New Jersey, and the likes. With the recent events in Pennsylvania and Virginia coming to an end, it is currently still legal in these two states to own and build an 80% firearm.

Again, check your local laws, but it is also not required in most states to ever serialize these firearms. There are a few “Do Not Dos” with 80% firearms though. For example, do not build one with the intent to sell it (“intent” being a keyword), as that is very illegal federally. If, however, in the future you decide that you don’t want it anymore, it is legal to sell or gift in most states. Whether you have to serialize it before this sale depends on your local laws.

The modular grip on the GST-9 is the main feature that makes this 80% frame stand out to me. If you want the options of 4 different configurations with one gun, this is the way. (Please get that reference…)

Final Thoughts

Before I dive into detail about why, I want to clearly state that I LOVE, LOVE, LOVE my GST-9 build! Of course, the slide, barrel, and internal components can influence this but with high-quality components, I am sure that you would come to the same conclusion as me. The way the GST-9 feels in my hand is as if it was designed specifically for me. The grip length is adjustable, so I can swap it around to whatever configuration I need for specific tasks. And the GST-9 comes already kitted out with modifications that are typically done to aftermarket Glocks such as the trigger guard undercut, the lack of finger grooves, the gas pedals on the front of the frame, the scalloped magazine release, and the texturized trigger guard to name a few.

The scalloped mag release.

The GST-9 has proved itself to be extremely tough and reliable through my testing, and I don’t even have a production model (which I am sure will be even better). The nickel-plated, extended length frame rail has been working as designed, helping the gun to run on little to no lubricant. And at the end of the day, I have noticed no unique wear and tear on either the slide or frame components. This means that the frame rails are installed perfectly and all the pinholes were drilled where needed. I contribute the success of this project mainly to the quality and precision of the jig as well as the same for the frame and rails. If you are tempted to start a project like this, I highly recommend the GST-9!

Learn more about the GST-9 HERE!

***Buy and Sell on GunsAmerica! All Local Sales are FREE!***

About the author: Riley Baxter is an avid and experienced hunter, shooter, outdoorsman, and he’s worked in the backcountry guiding for an outfitter. He also get’s a lot of enjoyment out of building or customizing his firearms and equipment. Check out Riley’s Instagram @Shooter300

{ 14 comments… add one }
  • sharky65 June 15, 2021, 8:47 am

    I ordered the GST-9 Pistol Frame (supposidly with a G19 and G17 backstrap) and the jig/toolkit combo. I knew going in it would take awhile to get the products I ordered so I can’t fault them for that, however, after a reasonable period of time I began requesting updates on delivery dates. Never got any real explanation just some vague information about how they were filling orders received 8 months previously. The company could do a much better job keeping their customers up to date on the status of their purchases.

    My second complaint involves the missing G17 backstrap that I never received. I realize mistakes are made but I’ve tried contacting them on 4 seperate instances about this and have had no response at all from 5D except their auto response when you contact them. I’ve advised friends and family members planning to do an 80% build to go elsewhere for their purchase. The product is good but don’t expect any support if you have a problem. Seems like 5D has zero customer support.

  • Lisa October 20, 2020, 8:43 pm

    Received my GST-9 10/15/2020 . It was ordered 1/1/2020 . I thought I would never get here but it came eventually. Be patient.

  • M W September 17, 2020, 11:43 pm

    Ha ha – I ordered one 6 months ago. There is exactly zero evidence anywhere that anyone has received one of these. Check their website, check 5d Tactical check Youtube – there are zero reviews.

    I finally requested a refund and still haven’t received one from 5d Tactical where I ordered mine. I’m filing a complaint with my state attorney general.

    Don’t fall for buying one of these. It’s a scam.

  • RANDY MARMES August 28, 2020, 2:39 pm

    Still waiting for ar and gst I orderad on 12th of july!

  • Glenn Roberts August 4, 2020, 11:46 pm

    I recently purchased the GST-9 full deal. I paid over $700.00 plus. My question is does it come with barrel and upper slide plus all upper internals??????? I can’t find my answer in all I read. Thank you in advance

  • Keith June 27, 2020, 10:40 pm

    I would like to buy this as a completed frame as I have multiple magazines from G26 to ETS 33rd. With my security occupation carry is a G17. Could you point me in the right direction to seller in Phoenix, AZ?

  • loraz April 21, 2020, 10:08 pm

    This WILL NOT take a G17 slide or barrel. You have to use a 19L slide and barrel. The locking block is different, and there will be no dust cover on the recoil spring.
    I contacted the manufacturer, and they confirmed this.

    • Devin June 19, 2020, 11:33 pm

      Does the frame come with a locking block or do I buy it separate, I know p80 includes it, do u know if the gst has it?

      • Mr Ed August 7, 2020, 11:17 am

        You need to buy the jig with the rails. However, I pre-ordered just after new year and still have not received it. (It was supposed to release in spring) In fact after asking for where I was in line, got the same answer beginning of June as I did beginning of August, that they’re shipping orders from November/December 2019. (Lies like mainstream media) So you maybe better off getting a P80 at this point.

  • I Love Liberty March 24, 2020, 6:11 pm

    I like Ghost guns. The tyrant politicians cannot stand them. Looks like a lot of work for an unregistered firearm though.

  • James March 23, 2020, 6:21 am

    What is the grip angle ? ( similar to 1911 ? Or Glock ? )

    • Michael Christensen March 23, 2020, 11:04 am

      I was just going to ask the same question, normal Glocks have to steep of a grip angle for my hand. I have to force my wrist over to get the sights to come close to each other.

    • tec void May 14, 2020, 1:56 am

      i read in the review that the GST-9 is the first kit gun that will fit OEM holsters, i would guess that means the grip angle is the same as a standard glock.

      • Brandon May 14, 2020, 6:54 pm

        The website says its 1911 grip angle

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