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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.
How to Build a Custom P320 thumbnail image

How to Build a Custom P320

80 Percent Arms   |   Feb 3rd 2023

The Sig Sauer P320 is a versatile and reliable handgun that is popular among law enforcement and civilian shooters. It features a striker-fired design and a modular trigger group that can easily be converted between different grip sizes and calibers. Building your own custom P320 allows you to tailor the gun to your exact preferences and needs, resulting in a more personalized and satisfying shooting experience. Seeing the final build before you is a remarkable feeling, as it was you yourself that put in all this work to create something you will be able to use day in and day out.

The Sig Sauer P320 Pistol

Much like other handguns on the market, the P320 is also available in a variety of models, including the full-size, compact and subcompact versions. When compared to other popular handguns on the American market, the Sig Sauer P320 is often compared to the Glock 19, Smith & Wesson M&P, and the Springfield XD. The Glock 19 is also a striker-fired handgun that is known for its reliability and durability. The Smith & Wesson M&P is a polymer-framed handgun that is popular among law enforcement and civilian shooters. Even the Springfield XD is a popular polymer-framed handgun that is known for its Frankenstein design and affordable price point.

P320 M18 Model

The P320 M18. Photo Source: Sig Sauer Configurator Tool

All of these handguns are widely available for purchase through firearms dealers and online retailers. The cost of the Sig Sauer P320 can vary depending on the model and customization options, but typically ranges from $500 to $1000. The Glock 19, Smith & Wesson M&P, and Springfield XD also have similar price ranges. Overall, all of these stock handguns are great options and the choice of which one to buy would be based on individual preferences, needs, and budget. That whole thought process changes though, when you enter the world of building your own custom Sig Sauer P320.

P320 Customization Options

A wide variety of modifications can be done to enhance the performance and personalize the look of the firearm. Some of the most common modifications include adding a new trigger, installing a new barrel, adding a new grip, and installing a new slide.

When choosing the right modification for your custom Sig P320, it's important to consider your intended use for the firearm. For example, if you plan on using your P320 for competition shooting, a match-grade barrel and upgraded trigger components would be a good choice. If you plan on carrying your P320 for self-defense, a custom grip module that provides a more comfortable and secure grip may be a better choice.

Exercise caution and follow all safety precautions. Always make sure the firearm is unloaded and clear before making any modifications. It's also a good idea to consult the manufacturer's instructions or seek the advice of a professional gunsmith before attempting to install any modifications. Here's a couple of YouTube videos that give some great tips for the part time gunsmith.

Sig Sauer P320 red dot sight installation

Apex trigger install video for the SIG Sauer P320

Below are some of my personal favorite and top market rated add-ons you can put on your P320 to keep giving your handgun that “new car feel” we all know and love. Understanding Sig's nomenclature, or naming sense, may take a while but you have a handle on it you'll be able to pick the exact parts you need to make a unique P320 perfect for your desires and needs.

Grip Modules:

  1. Grayguns P320 X-Series Grip Module
  2. Sig Sauer P320 X-Five Legion Grip Module
  3. Taran Tactical Innovations P320 Carry Grip Module


  1. ZEV Technologies P320 Slide
  2. Brownells P320 Slide
  3. L2D Combat P320 Slide


  1. StormLake P320 Barrel
  2. L2D Combat P320 Barrel
  3. Sig Sauer P320 X-Five Legion Barrel

Guides & Springs:

  1. Apex Tactical Specialties P320 Action Enhancement Trigger
  2. Grayguns P320 Advanced Trigger
  3. Sig Sauer P320 X-Series Trigger


  1. Sig Sauer P320 21-Round Magazine
  2. ETS Group P320 31-Round Magazine
  3. Magpul P320 21-Round Magazine


  1. Trijicon RMR Type 2
  2. Romeo1Pro 6MOA
  3. Vortex Optics Viper Red Dot Sight


1.  Herrington Arms HC320

2.  Agency Arms 419 Comp

Now we're going to make out a few builds here in just a second going over not just some different looks but also some varying sizes in the Sig P320 frames.

Building An 80% P320

Building a Sig Sauer P320 from an 80 percent lower unfortunately isn't possible anymore since JSD Supply discontinued the 80 percent fire control unit and the jig designed for it. But if you were lucky enough to snag one before their debacle with the ATF, hats off to you. If you still need to put together your 80% FCU below are the general steps you'll have to take to turn it into a 100%.

Step-by-Step Instruction:

  1. Set up the jig according to the manufacturer's instructions. This typically involves attaching the jig to the 80 percent lower using the provided screws and pins.
  2. Place the combined jig and P320 80% lower into your vise and prepare to drill.
  3. Use the drill press or milling machine to drill the holes and cut the slots as indicated by the jig. Be sure to work slowly and carefully, and to use the correct drill bit for each step.
  4. Hammer down on the FCU in order to shape the four metal edges into what will become your slide rails.
  5. Use hand files and a Dremel tool to smooth out any rough edges and to ensure proper fitment of the parts.
  6. Use a punch or drift pin to install the trigger and hammer pins.
  7. Install the trigger assembly, safety selector, and magazine release.
  8. Install the grip and slide release.
  9. Install the slide and barrel assembly.
  10. Install the guide rod and spring.
  11. Hit the range and test that bad boy out.

A few pieces of advice when milling out your 80% lower kit. Not all of these will apply to a polymer 80% lower kit but are just good knowledge to have:

  1. Cutting oil reduces friction and saves some of the lifespan of your drill bits.
  2. A spinning piece of metal is hot. Heat dulls the tips of your bits, especially if you are using lower quality metals in these bits. Carbide is king.
  3. Polish and really deburr the trigger guard and trigger well on your 80% lower. It will make the trigger pull smoother and keep your finger from rubbing.

Safety Precautions:

  • Always make sure the 80 percent lower receiver is unloaded and clear before beginning the build process.
  • Always wear safety goggles to protect your eyes from debris.
  • Follow the manufacturer's instructions and guidelines when using any power tools.
  • Always use proper safety equipment such as gloves and a dust mask when using hand files and Dremel tools.

Sig Builds

A few builds using  Sigs amazing gun editor, you can get some semblance of how you can modify your 80 percent kit to build something that looks like it just went to SHOT Show.

P320 RXP Full Size

P320 RXP Full Size

Photo Source: Sig Sauer Configurator Tool

Getting a bit of inspiration from those who don't wish to be flashy but know style when they see it. The classy all black with the gold accents has the looks equal to the performance.

Grip Module: X-Full Large - Black

Slide: X-Series 4.7" Slide Assembly - Black

Barrel: Full Barrel 4.7" - Gold

Guide & Spring: Recoil Assembly - 4.7IN

Magazine: Full 17RD Magazine - Legion

Optics: Romeo1Pro 6MOA - Black

P320 XCompact

P320 XCompact

P320 XCompact. Photo Source: Sig Sauer Configurator Tool

It's not about the size of the tool but rather how you use it. With a seemingly magical 15+1 in a handgun measuring barely 3.6 inches. It makes no sense why you would carry anything smaller on your person.

Grip Module: TXG Gull Med W/ Magwell

Slide: PRO-CUT 4.7" Slide Assembly - Black

Barrel: Full Barrel 5.5" Threaded ½ - 28 - Black

Guide & Spring: Recoil Assembly - 4.7"

Magazine: Full 21RD Magazine - Black

Optics: None

P320 X-Five Legion

P320 X-5 Legion with pro cut slide and threaded barrel

P320 XCompact. Photo Source: Sig Sauer Configurator Tool

It isn't everyday that you can check off all of the sweet upgrades you wish your pistol had. This is a very different story. Flared magwell? Check, Ported Slide? Check, Threaded barrel in the most common ½ - 28 thread pitch? Check. Having a really good day at the range? Check.

Don't forget you can actually opt for a slide that is shorter than your frame, incorporate a threaded barrel and compensator oh boy, you'll really be off to the races then. 

Grip Module: XCompact Small - Black

Slide: X-Series PRO-CUT 3.6" Slide Assembly - Black

Barrel: XCompact Barrel 3.6" - Gold

Guide & Spring: Recoil Assembly - 3.6"

Magazine: Compact 15RD Magazine - Black

Optics: Romeo1Pro 6MOA - Black

Build Your Next 80% P320 with 80 Percent Arms

To cap this all off, building a custom Sig Sauer P320 can be a rewarding and enjoyable experience for firearm enthusiasts of all skill ranges. The P320 offers a wide range of customization options to suit your personal preferences and needs. By following the steps and safety precautions outlined in this article, you can create your dream custom P320. How about it are you intrigued? Comment below if you'd be interested in us providing 80% P320 parts or kits!

Don't forget to check out 80% Arms for all your 80% Glock style pistol building needs and be sure to check out our related blog posts such as the FAQ for our GST-9, a polymer 80% lower, for more inspiration and tips.