How to Build a Gun “Off the Books”

You’ve probably heard that gun sales skyrocketed in 2020. Gun control laws have also taken root across the country. But you don’t have to hunt for a decent shooter, and you don’t have to pay a premium for whatever inventory’s left at the local gun shop. If you’re the survivalist or prepper who likes to be ready for any sort of “SHTF” scenario, you’ll enjoy this: Building a gun off the books. That is, fabricating a rifle or handgun, from scratch, at home with no serial number or paperwork. This is a weapon you can keep completely unrecorded and unknown to anyone but you, and most importantly…

The Legality of Building a Gun

Building such a weapon is completely legal to do under federal law and in most states. There are restrictions. Let’s look at what the ATF says. According to their website:

A license is not required to make a firearm solely for personal use. However, a license is required to manufacture firearms for sale or distribution. The law prohibits a person from assembling a non–sporting semiautomatic rifle or shotgun from 10 or more imported parts, as well as firearms that cannot be detected by metal detectors or x–ray machines. In addition, the making of an NFA firearm requires a tax payment and advance approval by ATF.

You can’t open up a gun shop in your garage and start selling homemade 1911s to the neighbors. You can’t build something like a short-barreled rifle or machinegun. You can’t buy an AK-47 parts kit on some European gun forum and weld it back together. And lastly, 3D-printing a gun that can slip through a security scanner is a felony. But most importantly, you don’t need to be a Federal Firearms Licensee (FFL) to build a non-NFA firearm. You don’t need anything at all, except for some tools and gun parts.

NFA & Restricted Weapons

Before we get to the tools and building the thing, what type of gun can we build? It’s easy to avoid all those other rules except for the NFA restrictions. Build a gun with a barrel that’s too short, and you made an SBR. Build a shotgun with a bore too big, and you’ve instead built an illegal destructive device. These are the NFA items you can’t build when you fabricate a firearm:

  1. A shotgun with a barrel shorter than 18”.
  2. A shotgun with an overall length less than 26”.
  3. A rifle with a barrel shorter than 16”.
  4. A rifle with an overall length less than 26”.
  5. A machinegun.
  6. A silencer.
  7. A destructive device
    1. Any missile or explosive with more than ¼ oz of charge.
    2. Any weapon that fires a projectile larger than 0.5” in diameter, except flares or pyrotechnics.

We’re left with quite a big field of guns we can legally build. We can make any handgun or rifle we want if we stick to these NFA restrictions. But building a gun from scratch normally requires advanced knowledge of machining and metallurgy. You’d need an entire workshop with CNC machines, lathes, and hundreds of thousands of dollars. You don’t need all that, thanks to something called a receiver blank.

80% Lowers and Firearm Receiver Blanks

When you buy a firearm, you need to conduct a background check, fill out paperwork, fill out more paperwork if it’s a handgun, wait for the background check to complete, and deal with an FFL. But there’s no federal law against buying something that’s almost a firearm and simply finishing the job someone else started. That’s where the 80% lower gets its name.

Firearm Receiver

Look at the two AR-15 lower receivers above. The Anderson stripped receiver on the right is a firearm under federal law. Even though it can’t fire a cartridge or chamber a round as it sits, it can be made to. It therefor requires a serial number and it requires a background check and paperwork to purchase. The 80 percent lower is nothing more than a piece of aluminum that looks kind of like a lower receiver. The Anderson receiver may be readily converted to expel a projectile by installing a parts kit and barreled upper receiver. That is how federal law defines a firearm: If the part in question isn’t designed to shoot a bullet and it can’t easily be made to without additional fabrication, then it’s not a gun and you don’t need an FFL to buy it. Since the 80% lower doesn’t have the pin holes for the safety, trigger or hammer, and since its inner cavity is solid aluminum, it doesn’t fit the definition. It’s “80 percent finished.” The ATF calls this type of firearm part a receiver blank.

Are Receiver Blanks Legal?

Yes. The ATF even has a detailed webpage clarifying whether an 80% lower is considered a firearm or not, with illustrations to show examples using the AR-15 platform. As long as the receiver blank in question doesn’t meet the definition of a firearm, it’s not subject to federal regulation by the Gun Control Act or the ATF. The AR’s 80% lower made this gun-building hobby popular. In recent years, many more types of 80% lowers have come to the market for various weapon platforms.

Types of Receiver Blanks

Unless you’re ready to foot the bill for that gunsmithing workshop, your choice of homemade firearm is limited to the types of available 80% lowers and frames on the market. Thankfully, some of the most popular rifles, handguns, and cartridges fit the bill.

AR Variants

The AR-15’s modular design made it a perfect testbed for new cartridges. Nowadays, AR-type lower receivers are available for the 9mm and .308 Winchester cartridges, with 80% receivers accompanying them for at-home builds.


Many new 1911s use aluminum frames instead of steel. It’s lighter, it doesn’t rust, and it can be easily machined. It only made sense that an 80% frame for the 1911 was produced from that same billet aluminum. The original 5” Government model, and the newer 4.25” Commander model are both available as a frame blank for custom builds.


A huge name in the 80% market, frame maker Polymer80 has most of GLOCK’s pistol lineup covered with their nylon-core polymer frame blanks. These P80 frames have become some of the most sought-after 80% receivers in the industry since they can be fabricated with just a few hand tools (a Dremel and sandpaper is all you need) and they’re compatible with all factory and aftermarket GLOCK parts.

Sig Sauer P320

Sig Sauer introduced the P320 handgun a few years ago. This unique pistol uses a modular internal chassis, a self-contained firearm that hosts the trigger, hammer, disconnector, safety, and other mechanisms. The interchangeable exoskeleton of the P320 includes the frame and grips, barrel, slide, and magazine. Only the chassis (officially called a Fire Control Unit, or FCU) is considered the firearm component of the P320 by the ATF’s opinion, so an 80% variant was produced that functions with all of Sig’s P320 parts.

Fabricating Your Firearm

The entire purpose of the 80% receiver is to make that jump from a box of bolts and parts to a working firearm as easy as possible – minus, of course, just buying the firearm component. Since most lower and frame blanks truly are 80% or so complete, the remaining work to be done requires little knowledge and only basic tools. Let’s focus on the AR-15’s requirements.

  1. Finishing jig & bits. A device called a jig is required to finish the lower. This is the other half to the project and it’s the second-most important part of the whole process. The jig performs most of the work, while you control the depth and rate at which your tools fabricate the receiver. The jig comes with the drill bits and end mill bits you need to fabricate the receiver.
  2. Drill press/mill, or router. At minimum, you need a drill press to cut and drill the lower receiver with the provided bits. A mill is preferred or a router can be used, but a drill press alone can get the job done, saving cash on equipment. Center-cut end mill bits are best for drill presses; these are typically the type of bits included with each jig.
  3. A vise will be used to secure the jig and lower while you work. To make milling as easy as possible, it’s recommended you use a cross-slide vise or X-Y table on your machine. That way, you’re not repositioning the lower each time.
  4. Cutting fluid. When machining metal, cutting fluid is required to keep the bits from overheating, dulling, chipping, or breaking. Some kits come with lubrication, but it’s best to buy a small bottle of oil from the local hardware store.
  5. All jigs come with the measurements and instructions for setup and use. Depending on the design of the jig and the exact receiver being machined, the measurements for fabrication may differ. Although the AR-15 receiver’s design is universal, it’s important not to rely on universal instructions.

Frequently Asked Questions about Finishing the Build

With your 80% lower fabricated, you now own a firearm under federal law. It’s functional and ready for the installation of a parts kit, upper receiver assembly, and a buffer tube with a buttstock or pistol brace. Assembling an AR-type rifle or pistol or some other handgun is beyond the scope of this article, but here are some of the most common questions and answers:

Q:  Do I need to do anything special before I order parts?

A: No. Federal law doesn’t require any special permitting or process for buying, shipping, or owning gun parts and receiver blanks. You will however need a Concealed Carry Weapons Permit if you intend to carry a gun on you.

Q: What about the state I live in? Are there restrictions?

A: Some states have banned gun-making parts and certain gun parts that aren’t considered firearms under federal law. Other states have outright banned receiver blanks, like New York and New Jersey. Always check your state laws before building any firearm.

Q: How long will it take to build a gun from start to finish?

A: Between figuring out what you want to build, ordering parts, fabricating your receiver or frame, and assembling your weapon, your first build could take a few days. The fabrication and assembly process usually requires an afternoon for a first-timer. An experienced builder with a good drill press or mill can fabricate a receiver and complete an entire build in an hour or two.

Ready to prove your new build? Check out our guide on choosing a rifle scope for short- and medium-range shooting.


Robert Dwayne

Robert Dwayne

To say that I am an outdoors enthusiast is probably an understatement. I am hyper passionate about everything outdoors: hiking, survival, hunting. On this website I am sharing my stories and experiences, and I hope you'll find inspiration to take up your own adventures!