I bought a couple of "armorer's barrels" that don't have barrel extensions.  I bought a couple of barrel extensions, but they do not index properly with the gas port.  Are there any options in making the barrel extensions index properly with the gas port (ie: stone/mill some of the barrel side of the barrel extension so that it will rotate farther and properly index with gas port - seems this may affect bolt fit/operation in the extension area).  Thanks for any help provided.

As the ext is shifted forward, length of the chamber decreaces. Proper way would be to cut the shoulder on the barrel till you get alignment, then rechamber to proper depth. Probably not something you want to try without a lathe, and not at all if these are chromed chambers.

That makes sense to me, but I have one concern.  When you say rechamber, are you just finish reaming the chamber or are you also taking an equivelant amount off of the chamber end of the barrel.  Seems to me that just moving the shoulder back would tighten up the space the bolt has to fit into between the "teeth" of the extension and the end of the barrel, possibly causing a lock up condition.  Thanks for your reply.

Not to imply that you don't know all that, but we need to be talking in the same terms. You need to consider that the ext locking lug face (the portion of the lugs inside the bbl ext) and the corresponding bolt lugs determine the length of the chamber. The rear face of the bolt lugs engage the ext lug face, and the resulting dimension from the bolt face to a tangent line on the shoulder taper determine the chamber length. When you move the bbl ext back, (unscrew from the barrel) you move the bolt face back (when locked) increasing the length of the chamber. Obviously, turning down the shoulder on the barrel(right way)or cutting the shoulder face on the extension (NOT the way to fit it!!) would move the bolt face forward and shorten the chamber. (Keep in mind that the locating pin has to be kept at the 12 o'clock position for proper bolt engagement). If you were to turn the shoulder that the ext fits up against till you got alignment with the gas port, you would then have to deepen the chamber a like amount. You could not reverse this and space the extension out or back till you got alignment, as you would have excessive and incurable chamber length. Probably an easier way to install an extension on these barrels would be to just abandon (weld up) the existing gas port and relocate a new one off the new extension. Doing it this way, there is no assurance that you can locate the gas port in a groove, where it should be.

Not to imply that you don't know all that, but we need to be talking in the same terms. You need to consider that the ext locking lug face (the portion of the lugs inside the bbl ext) and the corresponding bolt lugs determine the length of the chamber. The rear face of the bolt lugs engage the ext lug face, and the resulting dimension from the bolt face to a tangent line on the shoulder taper determine the chamber length. When you move the bbl ext back, (unscrew from the barrel) you move the bolt face back (when locked) increasing the length of the chamber. Obviously, turning down the shoulder on the barrel(right way)or cutting the shoulder face on the extension (NOT the way to fit it!!) would move the bolt face forward and shorten the chamber. (Keep in mind that the locating pin has to be kept at the 12 o'clock position for proper bolt engagement). If you were to turn the shoulder that the ext fits up against till you got alignment with the gas port, you would then have to deepen the chamber a like amount. You could not reverse this and space the extension out or back till you got alignment, as you would have excessive and incurable chamber length. Probably an easier way to install an extension on these barrels would be to just abandon (weld up) the existing gas port and relocate a new one off the new extension. Doing it this way, there is no assurance that you can locate the gas port in a groove, where it should be.

Once again thanks for the help.  Would you tac weld the old gas port using (then machine the diameter to clean up the area), say a TIG welder or would a cold weld material such as DEVCON Titanium or JB Weld be adequate to plug the hole.  Not sure the cold weld material can hold up to the temps of powder burn, but they are rated quite high in temp, around 350 degrees and 18800psi compression (and the old hole will be backed up with the gas block assy).  Sort of know that real weld is the right answer, just looking for opinions.  I really appreciate your help.

I did the same thing, bought a used barrel. Went to the next gun show and bought a new extension.  It was not indixed properly.  I went back and tried the others he had none were better but they were different.  Two monts later he came to the next show and then I tried the extensions he had that day and the third one was perfect.


Bobwrench

To plug a gas hole, I tap and put in a short set screw, being sure it doesn't project into the barrel, then weld over that.  Cold weld might work, but if it is rated at 18,000 psi, I would think that is substantially less than the 45,000 - 50,000 cup chamber pressure created in the .223. (I don't think there is a method of converting cup/psi). This does not in any way create an ideal situation, but the remainder of the old gas port will eventually copper/carbon up, and the barrel will be functional and usable. Not ideal, but usable. As with any other free advice, proceed at your own risk, ymmv, etc.

Understand the risk of free advice, but it is much appreciated.  Hadn't thought about setscrew in the old gas port, but a setscrew with the threads sealed with the cold weld materials I have available to me sounds like it would be a strong and sound seal.  Would like to try the random barrel extension trial that bobwrench used, but the gun shows here in SE Michigan are so weak, there rarely is an AR-15 table with enough inventory to try that.  All replies are appreciated.