Build your own AR Barrel from a blank | 358 Legend barrel Build

Building your own AR barrel a complete guide.


I ordered these parts to complete this 350 Legend (Modified 358) AR15 Barrel:

Barrel manufacturers recommend cutting off 1/2 to 1 inch from each end of the barrel. This is because the blanks are turned in centers with a lock dog and center tail stock. The centering tools wobble and wallow out the openings.

I chose to stick with a simple heavy barrel profile that uses a .936 Gas Block. Consulting with other barrel manufacturers who are making 350 Legend barrels, I acquired the gas port hole spec to be a carbine length #41 or #42 drill bit for ~.090'' gas hole.

Barrel Spec Sheet

A crude sketch lol

Contouring the barrel

Sticking with this simple design, I turned down the barrel starting at 1 inch from the chamber end. I then indicated the bore to 3 ten thousandth run out to get ready to cut the barrel extension tenon.

Cutting the tenon for the barrel extension

Since the AR locks up between the barrel extension and bolt face, it's crucial to setup the barrel extension tenon exactly plus ~5 ten thousandths for crush factor. This will setup for a better fit and headspace thus increasing accuracy. For this its recommended to use the bolt head that will be used for this barrel, matching its clearance. To figure out the barrel tenon length a depth gauge measurement is measured from the barrel extension face to the top portion of the bolt head. Most prints call for this measurement to be .625". Verify with the bolt head you plan to use and add 5 ten thousandths to 1 thousandths for clearance. Also notate the measurement to the bolt face to barrel extension. This number will be used to determine chamber depth when it comes down to chambering.

The diameter of the barrel extension tenon is stated .812" some prints will state .813". Threading for the tenon is 16 threads per inch. Once threaded, check fitment with the extension for a tight snug fit