Finishing an 80 lower and making your first AR-15 lower receiver is, mechanically, a relatively easy process – but there are quite a few steps involved from start to finish. What are they, exactly? What are some of the laws and best practices? Let’s look at an overview of finishing an 80 lower, so you can get to your first finished build!
The best way to approach this process is to understand both the physical and legal context: Physically, an 80 lower is an incomplete AR-15 lower receiver fabricated from aluminum alloys. It’s not finished being built, so it’s not legally considered a firearm. An 80 lower, metaphorically, represents a convenient and legal way to build an AR-15 pistol or rifle of different calibers at home – often saving you loads of money and avoiding state and federal government bureaucracy in the process.
Federally, the laws are pretty lax when it comes to building a firearm. As long as you can legally own a firearm, and as long as you’re building for yourself, there are generally no restrictions on the process – as long as you’re not trying to go full-auto, short-barreled rifle, or suppressed (you need documentation for those, first).
Unfortunately, your state may impose laws on the building and ownership of firearms that you should know, first. For example, California requires you to serialize your 80 percent lower before it’s built, and you have to meet a specific legal set of criteria for that serial #. Read up on your state laws before you start your build.
Points 1 and 2 were boring, but now it gets fun: You need to pick out the 80 lower receiver of your choice! There are plenty of things to consider: Caliber, type of alloy, finish, and aesthetic. Should you go with billet or forged? 5.56 or .308? Maybe 9mm? Phosphate-coated or plain Jane, rough aluminum? Lucky for you, we’ve got all the guides and articles linked above so you can answer these important questions before you buy (personally, we recommend our Premium Billet 80 Lower – read why here).
Building an 80 lower at home is easy! You don’t need much experience with, well, anything related to engineering or fabrication. Machining an 80 lower takes about an afternoon.
To build your 80 lower, you’ll need – you guessed it, an 80 lower jig! The 80 lower jig is just a big, hardened hunk of steel with precise measurements and shapes. Those measurements and shapes are what allow you, the at-home-gunsmith to tackle this job with no knowledge. The jig does all the hard for you. You just need a hand router (we prefer the Porter Cable Handheld Router) and a set of drill bits and end mill bits.
Now you’ve got your lower, your tools, your knowledge – you’re ready to build. You’ll need to strap that lower into that jig, hook up your router, tighten your end mill bits, and get cracking. We strongly, strongly recommend you watch through our video tutorials, first. This will give you a warm-n-fuzzy so you can anticipate the next step and take breaks and measurements appropriately.
Once you’ve finished that 80 lower, you’ll be the proud owner of a bona fide AR-15 stripped lower receiver. Now it’s time to throw in a lower parts kit and pick out your stock, buffer, tube, upper, barrel, muzzle device, handguards, and all that other jazz. You can pair your lower with one of our AR-15 rifle or AR 15 pistol kits or uppers, or you can buy a barrel, a stripped upper, and go piecemeal. It’s up to you!
Before you invest in that upper or lower, though, take one final gander all those state laws. Some states put serious restrictions on the configuration of your rifle or pistol. California, for example, has banned what their legislators deemed “assault weapon features” – get caught with a bayonet lug and a six-position buttstock, and you could be up for an extended stay in a gray, cinder block cell.