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Posted: 1/17/2010 7:45:01 AM EDT
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I have a Carbon-15 m4 that has been perfect for me but its starting to annoy me that the LMT rear sight has to be adjusted all the way to the left to be on target. I have read about a guy sending his back because the rail wasn't straight but I have a suspicion that the front sight base might be canted.
How can i check for cant and possibly fix it? |
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If it's a pinned A2 front sight base, there's not really anything you can do to 'fix' it. Every manufacturer puts out a few of those here and there. Most will usually just replace the barrel & FSB.
And you should be able to tell if its canted by looking at it, from the rear. If you have a flat top receiver, compare the plane of the picatinny rail to the FSB. The FSB should be perpendicular to the rail surface, and you can eyeball it if its not. |
| Very common problem. Someone once told me too invert the upper onto a flat, smooth surface (counter top), and see if all the ears on the FSB and the rear sight touch the counter top, or does the upper "rock"? Also, zeroing the irons at the range will tell a tale also.Read more here, about one third of the way down the page, question 5 in the FAQ for barrel changing. |
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If it's a pinned A2 front sight base, there's not really anything you can do to 'fix' it
of course you can do something.. Half of our group buy 14 Sabre Defense M4's had such canted sights.. What you need to do, is remove the frontsight pins, move the front sight out, and file (with a little round file) the pin holes on the barrel on the side of the barrel... By filing the holes (which are not holes actualy, but I on't know the words in english.. little trenches would be more descriptive), and putting the frontsight pins again, you'll progressively un cant the front sight post.. You need to file on one side, but can't remember which now.. If I recall well, the side in wich the sight is canted on. |
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Quoted: My SD barrel had canted sights too, and fired groups like a shotgun. I can't believe Sabre has the following that they do. IMHO they are crap. If it's a pinned A2 front sight base, there's not really anything you can do to 'fix' it of course you can do something.. Half of our group buy 14 Sabre Defense M4's had such canted sights.. What you need to do, is remove the frontsight pins, move the front sight out, and file (with a little round file) the pin holes on the barrel on the side of the barrel... By filing the holes (which are not holes actualy, but I on't know the words in english.. little trenches would be more descriptive), and putting the frontsight pins again, you'll progressively un cant the front sight post.. You need to file on one side, but can't remember which now.. If I recall well, the side in wich the sight is canted on. |
| Could be how the barrel was tourqed on or maybe there was too much room in the indexing pins slot in the upper.Heres how you know its canted or mis indexed.Put on a carry handle and turn the upper upside down and then when its on a flat level surface try and pass a pice of paper under the front sight bases ears if one ear is higher than another you will know its possibly a mis indexed barrel.It can be straight and canted to one side if the taper pins werent drilled straight with the FSB.I would take off the barrel and using thin soda can aluninum cut out a shim for around the index pin to snug it up in its slot.Youll be able to tell how snug when the barrel nuts lossened just wiggle the barrel from the muzzle end while the uppers in a fixture in a vise..just slight movement to either side will knock off the sites 6 to 10 inches..try that before you file anything..then if you cant determine send the upper back to the manufactirer and let them handle it. |
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Quoted:
Quoted:
My SD barrel had canted sights too, and fired groups like a shotgun. I can't believe Sabre has the following that they do. IMHO they are crap.
If it's a pinned A2 front sight base, there's not really anything you can do to 'fix' it
of course you can do something.. Half of our group buy 14 Sabre Defense M4's had such canted sights.. What you need to do, is remove the frontsight pins, move the front sight out, and file (with a little round file) the pin holes on the barrel on the side of the barrel... By filing the holes (which are not holes actualy, but I on't know the words in english.. little trenches would be more descriptive), and putting the frontsight pins again, you'll progressively un cant the front sight post.. You need to file on one side, but can't remember which now.. If I recall well, the side in wich the sight is canted on. I disagree... my Sabre Defense can easely group in a couple of inches at 300m, with very good groups.. but as a matter of fact, half over 14 carbines had canted sights. Nothing that you can't fix, but you shouldnt have to do this. |
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