How To Finish 80% AR-15 Lowers

How To Finish 80% AR-15 Lowers

Finishing 80% AR LowersAn 80 percent receiver is simply one that is not finished enough to be considered a firearm by the ATF. To the Feds it is a chunk of aluminum and can be purchased online without an FFL. You can finish it for your personal use as long as you may legally own a firearm but you can't sell it unless you're a licensed manufacturer.

Finishing a lower requires a milling machine or drill press, a fixture if you choose the drill press method, some drills and end mills and very basic machine skills. You're not going to save money. The beautiful billet lowers in the pictures came from Juggernaut Tactical. They currently sell the 80 percent lowers for $155 and CNC-finished lowers for $165, so cost isn't a factor.

I think most people tackle a project like this because they like making their own stuff. It's the sense of accomplishment more than anything else. It's going one step further than simply assembling a rifle kit from finished parts.

Over the years, I have built several 1911 pistols for my personal use. I didn't save any money. In fact, a gun assembled from individually purchased parts may cost you more than a factory-built firearm. Still, there is that satisfaction of building your own.


Finishing one of these receivers on my Grizzly Mill/Drill was not a big chore. AR-15 lower receiver blueprints are readily available online, and my main concern was calculating the dimensions from the drawings correctly. The holes for the selector (3/8") and trigger and hammer pins (5/32") were drilled first and they must be precisely positioned for proper function of the fire control group.


Once the holes were done, it was simply a matter of milling out the receiver pocket with a long 7/16" end mill and finally cutting the slot for the trigger with a long 5/16" end mill. Inside dimensions of the pocket are not super critical, and a few thousandths error probably won't be noticed.

One error I made was not cutting the rear channel deep enough into the buffer tube threads, and when I checked the fit of an upper receiver the takedown pin wouldn't quite line up. I milled in a little more clearance and the problem was solved. I would rate finishing one of these receivers on a mill as well within the capabilities of any hobbyist with basic machine skills.

Finishing a lower on a drill press is also possible. You will need a fixture that consists of plates that clamp around the receiver to guide the drills and end mills. The fixture from Juggernaut Tactical is very well made with the side plates drilled for correct positioning of the trigger pin, hammer pin and selector holes.

Three separate top plates are included for different steps of the machining process and a tool kit is available with the fixture which includes the drills and end mills you will need. Most of the aluminum is removed by drilling overlapping holes with progressively larger drills.


It is important to be able to set the depth on your drill press accurately with a dial caliper. In the final steps, the drill press is used as a router as the fixtured receiver is clamped in a vise and moved around the cutter following the pattern of the top plate.

You will need to maintain a solid grip on the vise as you move it around on the drill press table using the slots in the fixture as a template. A good video of this operation is available at the Juggernaut Tactical web site.

Test-fit an upper receiver to the lower when you think it is finished to make sure the takedown pin holes line up and the upper slides into position easily. Also, test fit a standard mil-spec hammer, trigger and selector to check function of the fire control group. The freshly drilled trigger and hammer pin holes will not be anodized against wear, so non-rotating pins may be a good idea for the final build.


Here's the raw 80% receiver as received from Juggernaut Tactical. The first step in the process is drilling the hammer pin, trigger pin and selector holes.
Norcross says finishing an 80% receiver is not a challenging job, but care must be taken to properly position the drilled holes. Check your measurements.
The receiver pocket is milled out with a long 7/16" end mill. Watch your depth! Keep in mind that the freshly cut parts surfaces will have no anodizing.
The finished receiver pocket. Not bad. With a secure setup and proper tool speeds, you can cut a nice, smooth pocket that looks as good as the factory version.
A hammer, trigger and selector are test-fitted to the completed receiver. Everything fits. A properly fitted 80% receiver can look as good as the factory unit.
If you finish your receiver in a drill press a fixture will be required. Note the clearly marked holes on the Juggernaut fixture. You can't screw it up.

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

Pioneer Arms PPS-43C Pistol

Pioneer Arms PPS-43C Pistol

The PPS-43 served Poland and the Russians during WWII. It is now available as a pistol for the US market.

Shooting the 20mm Lahti

Shooting the 20mm Lahti

David Fortier had the chance to fire the Lahti L-39 while filming the 2018 season of Guns&AmmoTV while on location at DriveTanks.com.

SCCY CPX-4 in .380 ACP

SCCY CPX-4 in .380 ACP

New for 2019 is the SCCY CPX-4, a .380 ACP semi-automatic pistol that extends beyond the existing SCCY CPX-3 line of pistols.

See More Popular Videos

Trending Articles

A $50 Ring Loc-Kit gives AirForce Condor airgunners unparalleled power and accuracy. Air Guns

AirForce Airguns Condor Ring-Loc Kit Review

Tom Gaylord - May 29, 2019

A $50 Ring Loc-Kit gives AirForce Condor airgunners unparalleled power and accuracy.

Governor Northam is calling a special session of the General Assembly on Tuesday, July 9th, to do nothing but pass more gun control! 2nd Amendment

Virginia Governor Northam Declares War on Gun Owners

Virginia Citizens Defense League - July 09, 2019

Governor Northam is calling a special session of the General Assembly on Tuesday, July 9th, to...

CRKT makes 17 different knife models exclusively for Ruger, from fixed hunting knives to tactical folders, and many of their models are offered in several different styles. Accessories

Ruger CRKT Knives Review

James Tarr - July 08, 2019

CRKT makes 17 different knife models exclusively for Ruger, from fixed hunting knives to...

Please sign and share the petition to get the required 100,000 signatures by July 27. 2nd Amendment

Tell the White House that the 2nd Amendment Was Not Given to the People by Government

Firearms News - July 02, 2019

Please sign and share the petition to get the required 100,000 signatures by July 27.

See More Trending Articles

More Gunsmithing

I have long been a big fan of Savage 110 series bolt action rifles. They are an extremely good Gunsmithing

Rebarreling a Savage Model 11

Gus Norcross - February 04, 2014

I have long been a big fan of Savage 110 series bolt action rifles. They are an extremely good

 Hobby gunsmithing will help you develop a variety of mechanical skills in shaping parts, attaching Gunsmithing

Basic Gunsmithing Skills

Steven Matthews - April 07, 2016

Hobby gunsmithing will help you develop a variety of mechanical skills in shaping parts,...

Melonite is very resistant to corrosion and is claimed to be a better treatment then hard chrome. Gunsmithing

Sarco Melonite Finished M4 Barrels

SGN Online Editors - April 30, 2014

Melonite is very resistant to corrosion and is claimed to be a better treatment then hard...

I rolled onto the range late in the afternoon with a couple rifles to test-fire. I had it all to Gunsmithing

Savage Trigger Upgrade From Sharpshooter Supply

Gus Norcross - April 02, 2014

I rolled onto the range late in the afternoon with a couple rifles to test-fire. I had it all...

See More Gunsmithing

GET THE MAGAZINE Subscribe & Save

Digital Now Included!

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW OUR CURRENT ISSUE

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Get Digital Access.

All Firearms News subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now