Non marring Leather mallet, hold onto the upper receiver upper only, and make the blows just above the barrel on the FSB to slip/re-index the barrel in the upper barrel socket.

If you’re good, then you should be able to re-index the barrel to less that two clicks off rear centerline of the rear sight at zero with two good blows.

Now having said that in regards to correctly indexing a installed barrel that is slightly canted, with your rifle shooting feet off at 50 yards with the FSB semi indexed with the upper receiver, you need to check for FS strikes/muzzle distortion from tightening the FS too tight, and/or a bent barrel or cracked upper socket (read you need to pull the barrel).

Quoted: i took off my HGs and i noticed that my bbl nut was loose, loose enough that i could manually move it--so i re-torqued it to the next notch (the one where i initially thought was too much....) what happens

Upper receiver barrel socket threads, barrel nut threads, and inner contact edge of barrel nut, and front face of the barrel extension all greased with moly.

Torque the barrel nut to 35 lbs, then the back the nut off, for a total count of three times (this mates the threads).  On the third tightening, take the nut the needed amount more to line up the barrel nut spines to allow the barrel nut to pass threw cleanly.  If you hit 80 LB of torque, you need to stop, back off the barrel nut and try again.

Hate to say it, and pray to the gods it didn't happen, you may have exceeded 80 lbs and either bent the upper barrel socket, or worse cracked the threads of the barrel socket. If this is the case, then the options are either replace the upper receiver, or if you can index the barrel (FSB) to zero and still keep the barrel extension lugs orientated to not bind on the bolt during cycle, you will have a canted front sight on the rifle when zeroed.

If you mean that the FSB/gas port is not aligned/indexed with the barrel extension/extension pin (like within a degree or two), then the barrel needs to go back as a defective unit and replaced with “in spec” unit.

Granted that there is always the option of widening the upper barrel socket pin slot and using shims, but this will only buy you a few degrees until you have rotated the barrel so far around in the upper receiver that the bolt/extension lugs will not work with each other correctly (binding on engagement/release).

Time to pull the barrel,

And if the barrel is within spec, this time bore sight the barrel with the iron sights before calling the barrel install good.

Quoted: have you tried a 3 pound hand sledge hammer, and a piece of leather to protect the finish?

You might get away with this heavy of a hammer (force) on a forged FSB, but if you try that much force on a casted FSB, you can kiss it good-by.

Dano523,

I've fixed two Bushy barrel alignment problems by ever so slightly opening up the indexing pin channel in the upper and shimming it as you descibe in one of your previous posts.  The amount of metal I needed to remove from the notch was very minimal.  The shims were VERY tight and there was absolutely no barrel movement after the shims were installed.  Both rifles then could be zeroed with the rear sight nearly dead center.  I think one of the rifles was still one or maybe two clicks off mechanical zero.

Both rifles shoot very well and have not experienced any problems.  One has several thousand rounds through it.  The other has maybe only 300 rounds through it.  I'm pretty good about checking the lug areas when cleaning and have seen no signs of anything out of the norm.  

Should I be expecting anything bad to happen to either rifle in the near future?  

Seriously, I'm interested in your thoughts on potential problems either of these rifles might encounter.

Thanks!

Indexing a barrel is semi normal practices during a barrel install on civilian rifles.

Standard spec for the military is the rear sight has to be within 13 clicks off center to be acceptable. A target shooter want the rear sight to be dead center since cranking the windage knobs is standard practice, and with a dead center zero, to have a known return windage point to come back to.

In regards to your question/concern, a simple test to confirm that the bolt is not binding is to do a 45* drop test or just stick you finger in the back of the carrier and feel if the bolt lugs and the extension lugs are binding on pass threw.

As a general run for re-indexing, if you can zero out the rifle with the rear sight (even if all the way over to one side), then you should be able to index the barrel without problems.  It's when you have the rear sight cranked all the way over, and you still not zeroed that chances are you will end up rotating the barrel extension in the upper barrel socket too much, and have lug binding or the feed ramps just way rotated to allow a clean feed.

As for shimming or using the leather mallet, both work fine, and it just boils down to how much time you have on your hands and if you plan on shimming, to have the tools needed to pull the barrel.

Myself, I shim all my match rifles at barrel install (read get the gas port TDC) and then use the adjustable front sight to fine tune at the range live fire zeroing. As for my service rigs (at this point in my life, the rigs I try to burn up on a yearly bases), they get the leather mallet since sooner or later the rifle it going to take a hit anyway. Plus, I'm not up for the multi re-indexing/shimming game that you have to play to fine tune between trips to the shop and the range (like a perfect zero really matter when your busting/burning up rifles on a fixed FSB anyway) .


Hope this answers your question.

Quoted: Dano, What are you using for shims in this procedure of yours??

Pepsi can

Thanks, Dano523.  That did answer my questions/concerns.

I've always thought a lot of your posts.  You've been very helpful and I've learned a lot from you over the past few years.  Thanks for sharing the knowledge and experience.  

Mark

ar-wrench,

Yes, this is a upper receiver block offered by DPMS, and allows bore sighting to iron sight shooting with the upper still in the block.  

As for the clamp type blocks, you just need to pull the upper out of the block to bore sight. No reason to wait until it's live fire time to see if you have installed/index the barrel correctly.
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Boog,
You should always check headspace on a build, no matter if the parts are new or used.
The catch can be finding the specific headgauge for the chamber that you are using (223. 5.56 wylder, or 5.56 Nato) to get the correct readings.