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Posted: 9/20/2003 7:51:37 AM EDT
I picked up a used upper and the front sight is canted off to the right. I am having to crank the rear adjuster all the way to the left and it's still shoots about 2" to the right. It has a factory break pinned and welded but it looks like the guy took something and clamped to it to unscrew it , could he have put enough force on it to cause this and how can I correct it ...thank's
Link Posted: 9/20/2003 9:19:41 AM EDT
Originally Posted By bushbanger: I picked up a used upper and the front sight is canted off to the right. I am having to crank the rear adjuster all the way to the left and it's still shoots about 2" to the right. It has a factory break
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First of all, it's called a "brake" and it has nothing to do with your front sight problem. So forget about it.
pinned and welded but it looks like the guy took something and clamped to it to unscrew it , could he have put enough force on it to cause this and how can I correct it
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This is a very common problem, caused by a small error in the upper receiver barrel pin slot. If you're capable of installing a barrel, this is an easy fix. Remove the barrel, take a jeweler's file and very carefully open up the slot in the upper receiver to let the front sight come up straight. I've found that just eyeballing the sights works very well, but if you're picky, tie a piece of thread through the rear sight aperture to the front sight blade and any errors in sight alignment will be obvious. Once you have the barrel/front sight straight, you need to tighten up the slot so the barrel won't move when you tighten the barrel nut. With the barrel in place (the barrel extension acts like a little anvil) take a small hammer and punch, and very lightly peen down the treaded area on the loose side of the slot. Careful, it doesn't take much!!! Just a few light taps are all that's needed. Once you get the barrel straight and have removed the slop in the slot, reinstall the barrel and you're done. Easy, huh?
Link Posted: 9/20/2003 10:25:47 AM EDT
[Last Edit: 9/20/2003 10:33:13 AM EDT by shamayim]
What Homo didn't bother to mention is that your front sight isn't canted to the right. It's tilted LEFT. That's why you're shooting to the right. Also, keep your files in the drawer until you get the thing apart and take a look at what's really going on. The vast majority of these right shooting situations occur because the barrel was over enthusiastically tightened on assembly, and the locating pin on the barrel dug into the left side wall, pulling the whole front sight assy over with it. If that's the case here, and the odds say that it is, what you need is a shim; not a file. Take the barrel out, than reinsert it, meking sure that the locating pin is fully bearing against the right wall of the channel. Then start inserting feeler guages in the left side of the channel. My hunch is that you'll find that you can get at least a .0003 guage in there; possibly more. When you get to the thickness that won't fit, go back to the thicknes .0001 less than the last one that did, and snap a chunk of it off in the slot. That'll keep the barrel from rotating bck when you tighten it. If, in fact, you have no open area to the left, that's the time to go with the file on the RIGHT sidewall, just a thousanth or two at a time. The alignment technique suggested above is pretty crude, but I guess it'll at least get you into the ball park. [:D] [Edited to add] Why do I think this is a Bushmaster upper? Maybe because they were famous for the overtightening number a couple of years ago. They had apparently hired some assemblers who didn't have a clue, and for awhile we were getting almost daily reports on the site about brand new Bushies shooting to the right.[;D]
Link Posted: 9/20/2003 11:36:59 AM EDT
[Last Edit: 9/20/2003 11:38:59 AM EDT by Homo_Erectus]
Originally Posted By shamayim: What Homo didn't bother to mention is that your front sight isn't canted to the right. It's tilted LEFT. That's why you're shooting to the right.
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If you read my post you'll see that I don't even mention "left" or "right" - only to bring the front sight up "straight."
Also, keep your files in the drawer until you get the thing apart and take a look at what's really going on. The vast majority of these right shooting situations occur because the barrel was over enthusiastically tightened on assembly, and the locating pin on the barrel dug into the left side wall, pulling the whole front sight assy over with it.
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I, too, have seen this happen when someone uses barrel blocks and a torque wrench - the preferred method in the Mil TM, BTW. But far more often it's merely a sloppy or miscut slot in the receiver. At least half of the barrel installs I've done needed to have the slot "adjusted," including mounting new Colt barrels on new Colt receivers. Before I screw on the barrel nut, I test fit the barrel and check the sights for alignment.
If that's the case here, and the odds say that it is, what you need is a shim; not a file.
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Forget the shim - try the peening method. Like trying to tighten the barrel nut several times and torque it down, shims just needlessly complicate a simple operation.
[Edited to add] Why do I think this is a Bushmaster upper? Maybe because they were famous for the overtightening number a couple of years ago. They had apparently hired some assemblers who didn't have a clue, and for awhile we were getting almost daily reports on the site about brand new Bushies shooting to the right.[;D]
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Sad, but true. Many of the guns I've done this little trick on have been factory built guns - Colt, Bushmaster, Olympic, Model 1, ASA, etc. The only brand I don't think I ever had to correct like this is an Armalite.
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