All,
Just got threw watching the AGI armorers video on the AR15 but they didn't cover the barrel removal. From what I could gather, the barrel extension has the pin that aligns the barrel to the receiver. Looking through my Bushmaster catalog, it looks like all of the barrels come with barrel extensions which thread onto the barrel so my question is:

Is is possible to get a barrel that is not properly aligned with the pin on the barrel extension causing the front sight to be canted slightly?

If so, I don't see any tools for removing or reindexing a barrel extension.

Thanks,
Mavic

Possibly, but the usual cause of a canted front sight is improper installation of the barrel assembly onto the upper receiver.

The upper receiver has a slot into which the alignment pin on the barrel extension fits.  If excessive torque is applied to the barrel assembly during installation, the alignment pin can dig into the side of the slot, damaging the slot and causing the barrel assembly to twist out of alignment as the barrel nut is torqued.

To avoid this problem (or correct it on a rifle with a damaged alignment slot), clamp the upper receiver in an armorer's block instead of clamping the barrel in a barrel vise.  Proper lubrication of the parts also helps avoid the problem.  Ideally there should be no torque applied to the barrel assembly as the barrel nut is tightened.

California_Kid,
Thanks for info. So is it standard for a new barrel to come with a barrel extension already installed so that the possibility of incorrect indexing is eliminated?

If not, where would one get the tool to properly align and tension the barrel extension and pin?

I've checked my Sinclair and other catalogs and can't find anything for the barrel extension.

The extension is what determines the headspace. The barrel should be headspaced before the front sight base pin holes and gas port hole are drilled. Most barrel mfgr's supply the barrel headspaced, drilled, and sight base installed. A few will sell the barrel as a "blank"; no holes or sight, and if requested, no extension.

Several vendors have extension wrenches - I saw one at Del-Ton -[url]http://www.del-ton.com/tools.htm[/url]

Thanks!! I guess I won't have too much to worry about when the time comes to get that new barrel.

Thanks Again,
Mavic