Quote:
Originally Posted by Triggernosis
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 |
This is pretty much it.
In some cases, you may have just a bit of play between the indexing pin on the barrel extension and the upper receiver, and this can result in the front sight in a pinned gas block assembly being very slightly off the vertical relative to the rear sight.
However, it has to be way off before it becomes an issue that precludes properly zeroing the rifle in windage and elevation.
If you've got a barrel that does not yet have the holes for the gas block pins reamed, it's a total non issue as you can level the gas block and front sight with the upper receiver before you ream the holes.
The same thing applies if you've got a gas block that clamps onto the barrel.
The last few times I've changed barrels on my service rifle AR-15, I've used a Compass Lake barrel that has four flats on the barrel designed to engage allen screws in the front sight base/gas block that allow you to true up the front sight. It's pretty idiot proof.
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I've done numerous AR-15 builds and I've only encountered one where a tooth on the barrel nut, when properly torqued, aligned with hole for the gas tube in a manner that caused a problem.
In that case, backing it off for clearance allowed the barrel to rotate slightly, and tightening it up enough to clear resulted in what I felt was excessive torque. The issue was some out of spec parts, but the quick and dirty solution until I got a proper barrel nut was to just Dremmel off the offending tooth and go with the proper torque value.
Shimming is another option in that situation, a better one if you do not want to replace the offending part, and if you have the proper tooling, you can also lap and square the face of the upper receiver - but that's pretty advanced stuff and does start to mess with the design dimensions, which can cause as many issues as it solves.
But...buy quality parts and it will not be an issue.
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Putting a barrel on an AR-15 is a lot easier than re-barreling an FAL where you have to take much more care in timing the barrel to the receiver - and in some cases will have to stipple, shim or turn a surface to get the proper torque, and it's a lot easier than working with an AK where you have to press the barrel into a trunnion while ensuring it is properly timed.