Quote:
Originally Posted by torizus
What I learned in my three builds as a beginner.
The barrel has an extension ring that is attached precisely to establish the correct head spacing. This extension also has an indexing nib that aligns into the indexing slot on the upper. Most barrels come with the extension attached and adjusted, if not, you will need the proper tools and knowledge to attach it. This is where major problems arise in attempts by first time builders. Incorrect head spacing is usually catastrophic in any firearm. Make sure your barrel has the extension ring attached when you buy it.
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This is correct. ^^^
As a competitive Service Rifle shooter, I change my barrel out about every 2,700-3,000 rounds, which is at least once a year for me. One of my uppers has had about 7 or 8 barrels on it and I expect to keep on replacing the barrels on it for the foreseeable future.
Indexing the gas tube isn't that difficult either. Crank the barrel nut down to near the proper torque and then check to see if the gas tube will line up. If it doesn't line up just perfectly, either crank a bit tighter or loosen it up a bit until it does. That's really all there is to it.
I highly recommend the two following tools for doing the job:
PRI Barrel Nut Wrench AR-15
Geissele Reaction Rod AR-15 Vise Block Steel