cc-settings-icon BUILD AT HOME
80% Arms sells AR-15 and .308 80% Lower Receivers, 80% Lower Jigs and other accessories which allow you to legally build a firearm at home in most states.
We utilize state of the art 5-axis CNC machines to mill all our .308 and AR-15 80 percent lower receivers to incredibly precise tolerances using premium billet aluminum.
We also offer our patented AR-15 and .308 Easy Jigs which is the first 80% lower jig that makes it ridiculously easy for a non-machinist to finish their 80% lower in under 1 hour with no drill press required.
Products manufactured by 80% Arms carry a lifetime warranty against manufacturing defects. We will promptly replace or repair any product that we determine to be defective.

GST-9 MOD1: Instructions and Troubleshooting

Instruction Manual

Video Instructions

Which Jig Do You Need Help With?

I have the polymer GST-9 jig.

Continue scrolling below for some FAQ's about the polymer jig. 

I have the GST-9 Infinity Jig. 

Please click here for more information and details. If you wish to return to the product page, click here

Frequently Asked Questions 

Can I shoot calibers other than 9mm with the GST-9?

Yes! The GST-9 can shoot 9mm, .40cal, and .357SIG. We have a great blog that shows all the different ways you can build out your new GST-9.

What parts do I still need to build my gun?

You will need a lower parts kit, a magazine, a slide, a barrel, recoil spring, slide completion kit and iron sights or a red dot. It's not as much as it sounds! Whichever parts you choose, please note that they must be Glock 19 Generation 1-3 compatible.

How Do I Install A Lower Parts Kit (LPK)? 

We made y'all a video to help you do just that! You can view that here.

How do I install my modular grips?

Use the 3/32 x 1/2” pin included with your jig kit to secure the front of the grip. Use the 3/32 x 7/8” pin to secure the rear section of the grip. Both pins must be used to properly secure and align the grip to your pistol frame. Before tapping in the pins, examine the tip of the pins. Insert the side of the pin that has a chamfer (tapered end) first. Use a 3/32” punch to avoid damaging or marring your frame when tapping in the pins. Punch kits for your GST-9 are available here.

My handgun isn't cycling well, what do I do?

First, make sure that all plastic has been completely removed and sanded smooth. Tolerances are tight, so if you leave a little plastic, the friction on the slide can impede travel. Second, make sure all components are installed correctly, and lubrication has been applied where necessary. Lastly, when working new parts in together (especially from several different companies as is common in handgun builds), make sure you are using full-power ammunition (steel-case ammo is notoriously under-powered), and allow a break in period of 200 rounds. Still having issues? Send our support team a message on our Contact page, or by sending us an email at: 

I ruined my frame, what do I do?

We're here to help! Review our Warranty Policy, and Contact our Support Team. 

What is the difference between the GST-9 Gen 1 vs Mod 1?

Over the last year, we've taken customer feedback with our GST-9 and made various improvements based on customers’ combined experiences. These are the functional enhancements:

  • The front rail now has an open channel design, making it easier to remove debris from drilling the frame. 

  • The shape of the gas pedal has been changed for easier drilling and enhanced  ergonomics while shooting. 

  • The slide lock lever section has been scalloped for easier slide removal. 

  • Towards the rear of the frame, we have updated our rear rail to a two-piece design. It reduces the likelihood of the rails being bent from possible pin misalignment. 

  • The full sized grips now have stippling for a more comfortable and secure grip when handling.

Benefits and Difference between NiB and Black Nitride Coating in rails selection?

Nickel boron or NiB is an electroless nickel based plated coating with self lubricating properties and a very low coefficient of friction for increased reliability. Black nitride is a surface conversion that diffuses into the material, altering the chemical make up for increased hardness, improved strength, and ultimately better durability. We provide options as there are many aftermarket slides with various coatings. The choice allows users to personalize the rail coating that best suits each individual build.

Why two piece rear rails?

It reduces the likelihood of the rails being bent from possible pin misalignment. It also simplifies rear rail pin installation.

What products work with what version?

  • The GST-9 Infinity Jig works with both the MOD1 and V1 frames.
  • Mod 1 jigs are backwards compatible with our original GST-9.
  • Original jigs do not work with our Mod 1 frames.
  • Front rails will work in either version.
  • 2 piece rear rails only work with Mod 1 GST-9s.
  • Compact/full sized grips only work with corresponding GST-9s.
  • All other 3rd party products will work with either as they still use Glock Gen 3 parts.


















Does Wraith Slide work with both GST-9 versions?

The Wraith slide will work with both versions as the slide is designed to be Glock 19 Gen 1-3 compatible.

Will you still offer support for the original GST-9?

We back all of our products, including the GST-9, with our lifetime warranty. Contact our support team if you need any assistance and we will make sure to take care of you!

Mod 1 - Jig's 6th Hex Nut and Black Bolt

The 6th hex nut and longer black bolt are meant for the hole in the bottom corner of the square standoff which is closest to the “MADE IN USA” text. 

The longer black bolt can only be used in this hole and is not interchangeable like the rest of the silver bolts. The longer black bolt is the only one long enough to clear and reach all the way through the cross section of the standoff. Using it in any other fastening hole will cause it to stick out from the surface of the jig.

When tightening/loosening the 6th hex nut and longer black bolt, it may be useful to use an open ended ⅜ wrench or crescent wrench to prevent the nut from free-spinning. The black bolt along with all the silver bolts  should be finger tightened until snug in order to minimize any gap between the two jig halves.

Black Nitride Wearing Off 

Black nitride or ferritic nitrocarburizing is a surface conversion that diffuses nitrogen and carbon into the top layer of ferrous parts, such as steel rails, changing the composition of the steel, rather than being a surface coating on the top of the steel such as NiB, Cerakote, or DLC 

FeO4 or ferrate(VI) is a byproduct of the ferritic nitrocarburizing process when the iron (Fe) in the steel rails is oxidized. This “free” iron on the surface is saturated with carbon which is what gives the parts a black appearance. 

Although the “black” color can wear away, the benefits of black nitride, such as, increased hardness and improved strength, as well as, wear resistance and corrosion protection, are literally baked into the steel rails and does not go away without physically removing material from the rails. 

Slide not locking back after last round

If a slide is not locking back after the last round is fired, first check if the slide locks to the rear on an empty magazine when manually racking to rule out underpowered ammunition and/or an overly stiff recoil spring.

If the slide does not lock back when being manually manipulated, it is likely the slide stop lever is not being engaged by the follower of the empty magazine. This will often be accompanied by the magazine not dropping free because the sharp point of the slide stop lever engagement tab is not on the top of the follower and is barbed into the side of follower, trapping the magazine. 

Check that the slide stop lever is seated in one of the groves of the trigger pin and that it can rotate freely up and back into place under its own spring pressure. 

If available, try a different magazine, preferably from a different manufacturer (i.e. ETS, Glock, KCI, Magpul). 

If the problem persists, check that the slide stop lever sits tightly along the side of the frame without gapping between the lever and the frame body. If the serrated portion of the lever separates from the frame towards the bottom, bending it square can eliminate the play in the slide stop lever when installed.

Standard engagement between slide stop lever to follower of empty magazine:


Missed engagement between slide stop lever to follower of empty magazine:

Loosely bent slide stop lever on side of frame:

Re-bent slide stop lever on side of frame:

Your FAQ Doesn't Answer My Question, How Do I Get More Help? 

You can live-chat us during business hours, e-mail us, call us, or even drop by if you're local! All information is on our Contact page.