When I left the Marines in the mid-90s I got a job working the gun counter at a small sporting goods store. We only stocked one AR-15 rifle at a time. Back then, it would be hard to imagine how common this rifle would become. According to the National Shooting Sports Foundation (2013), AR-15 rifles account for nearly 20% of all U.S. firearms sales. The AR-15 is our generation’s M1 Garand or 1903 Springfield.
I’ve always wanted to machine an AR barrel from a blank. While it seems complicated to some, the techniques used to chamber an AR-15/M16 M4 barrel are very similar to those used to chamber a barrel for a bolt action rifle.
This project is going to start with a Shilen match barrel blank. The blank is straight, with no contour and has a rifled bore machined through the center. The blank is 29.5″ long and 1.200″ in diameter- it feels more like an axle then a barrel when you pick it up.
I’ll be building a rifle with a 16.5″ length, and a Special Purpose Rifle (SPR) type profile. If you spend a little bit of time on the net, you can find some excellent drawings of barrel dimensions. The best drawing I could find for the critical dimensions, such as gas port location, is found here. You’ll notice the profile is different from the one I am turning, however, the other critical dimensions are the same.
So, why fabricate your own AR-15 barrel? Well, I did it for the challenge; but, if you wanted to chamber your AR for a wildcat cartridge, or faced some sort of parts shortage, your own barrel is just a few hours away on the lathe.
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I ordered the following items from Brownells:
- .224 9 Twist stainless-steel unturned barrel blank (787-922-090)
- Barrel extension pin (231-000-082)
- Barrel extension AR15/M16 M4 barrel extension (080-000-574)
- 3/8″ High-speed steel turning kit (080-000-835)
- High-speed steel 35 degree profile kit (080-000-836)
- 1/2″ threader (080-000-839)
- Starrett Dial indicator (749-007-761)
The reason I cut off both ends of the blank is because Shilen (and most barrel makers) recommends it. As tooling enters and exits the barrel blank, the ends can open up. Cutting off the ends, removes these out-of-specification sections.
I turned the first 2.25″ in front of my barrel extension to a diameter of .980″, then reduced to .840″. The gas block will sit on a section of barrel .750″ in diameter. This gas block shoulder is located 8.750″ from the front edge of the barrel extension and is 2.000″ long. A detailed drawing of a Bergara mid-length barrel can be found here.
While the barrel was still between centers, I used some 220-grit abrasive cloth coated in oil to polish the finish.
With the correct headspace achieved, I cut a small feed ramp on the rear of the barrel. Unfortunately, I forgot to take a picture of it, however, a picture of this recess can be found in this article on the Brownells website.
The gas port is located .300″ from the rear edge of the gas block cut step.
Machining an AR-15 barrel from a blank was a rewarding endeavor. If you ever wanted to give it a try, go for it, you’ll be happy you did!