When installing a new barrel assembly, how do you correct for a front sight that is canted slightly to the right?  How does the front sight become canted in the first place?

Quoted: When installing a new barrel assembly, how do you correct for a front sight that is canted slightly to the right?

A fellow here, Homo-Erectus, has a post or two about filing open the indexing notch in the upper on one side, inserting the barrel and then peening the other side with a punch.  Sounds like it would work but have never done it myself.

How does the front sight become canted in the first place?

Poor indexing with the extension pin when drilling the front site base pin holes.

Here's what Halfcocked mentioned:

Copied from Homo_Erectus:

The Famous Homo Erectus Barrel Mounting Method -

You'll need an Action Block and a Barrel Wrench, and that's all the special tools you'll need. I'm assuming you already have a vise, hammer and punches, files, and circlip pliers.

Forget the torque wrench and all those silly "tighten and loosen 17 times while waving a dead cat over the barrel nut and dancing naked in the moonlight chanting voodoo curses with your nutsack smeared with magic moly grease" procedures incessantly parroted my the Worshipers of Military Manuals who until recently confined their insanity to the Troubleshooting board but have now starting to infest and infect "Build it Yourself." In order to install an AR barrel, all you have to to is tighten a single nut until the notch lines up.

But first, stick your new barrel in your upper receiver and make sure there's no play in the barrel pin notch and the front sight base is straight up and down. If it's not, take a jeweler's file and open up the notch to bring the front sight base up straight. You can tighten the notch to remove all slop (very important!!) merely but taking a small hammer and punch, and with the barrel in place very lightly peen down the threaded area on the "loose side" of the notch. Be careful, use very light taps because it doesn't take much!!

Now that the front sight is straight, all you have to to is tighten one nut. I use a short (2-3 inch) stub of a gas tube in the bolt carrier key pushed into the upper receiver to keep the circlip, weld spring, and delta ring indexed. Spin the barrel nut on until it's hand tight, then lean on the barrel wrench until the next gas tube notch in the barrel nut lines up. If you're using the gas tube stub in the bolt carrier, you'll see it pop through the notch.

That's it!!! STOP!! You're done!! Install the gas tube and handguards and go shooting!!! The whole process should take less than 20 minutes. If it takes longer, you skin your knuckles, or you have to loosen and tighten the nut more than once, you're doing it wrong!!!

Mike

Another method is to drill out and run a tap through the holes in the site base and use set screws.  Probably not as durable as the taper pins but unless you're really going to abuse your rilfe it works fine.  I do have a couple of ARs with their front sites mounted this way.

If it's too far off, opening up the slot on the receiver could possibly cause the barrel extension to rotate enough not to allow the bolt to close.  But, if it's not too far off, it shouldn't be a problem.  I've done two things in the past which have worked for me.

1. Remove the sling swivel and drive the pins out.  Remove the front sight base, and tap the hole in the housing under the sling swivel, for a set screw.  Reinstall the sight base, line it up correctly, and tighten the set screw.  Verify that it's on straight by zeroing the rifle at the range.  Reinstall the pins, re-reaming if necessary.  I drilled mine out for 1/8" dowel pins vs. the taper pins to straighten mine out and it worked fine.

2.  If you do use the method of opening up the slot on the receiver, you can also install an oversize index pin on the barrel extension to tighten it up, rather than peening it.  Peening it is probably easier and less time consuming, but I took out the index pin, redrilled the barrel extension for a larger diameter pin, and tightened up the slop in a receiver that way.  

How do you remove the indexing pin??? Does it involve removing the barrel extension???

Thanks for all the responses and help.

Quoted: How do you remove the indexing pin??? Does it involve removing the barrel extension??? Thanks for all the responses and help.

There have been very few, but every indexing pin I have tried to remove was basically destroyed trying to remove it (they are in pretty tight and vise grips and such tear them up).  There should be absolutely no reason to remove the indexing pin to correct a canted FSB.

I just corrected one last weekend and I did the filing thing on one side, then I fabricated a small, brass shim the made up the gap created by the filing process and installed it on the opposite side of my filed area.  This shim fit tighly enough that I had to tap the barrel into the receiver, sandwiching the shim between the index pin and the receiver.  I left excess material sticking up so that I could fold the shim over the index pin.  I am thinking that with the shim firmly sandwiched between the index pin and receiver in addition to the shim being folded over the index pin and being captured by the barrel nut, this shim is going nowhere.  The cant was fixed, not mechanically perfect but it was one line left of mechanical center vs. being nearly hard up all the way left.

Adding:  IIRC, I ended adding a total of 0.020" of shim on the opposite side of the filing.  That's not alot in the big scheme of things, but think about how far that made the front sight post, which is 2+ inches above the center of rotation.  It worked.  Messing with the index pin really shouldn't be necessary.

I just corrected one last weekend and I did the filing thing on one side, then I fabricated a small, brass shim the made up the gap created by the filing process and installed it on the opposite side of my filed area. [\quote]

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I filed the receiver notch slightly and it was enough to correct the FSB cant. Now ill peen or shim the other side and also wait for my receiver vice block and barrel nut wrench to come in via UPS.

Thanks again to all who responded with info and help.