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Posted: 7/27/2006 7:12:08 AM EDT
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Hi All, This is my first AR and I bought it used. My problem is that the front sight block(FSB) is canted to the left slightly which is causing the windage adjustment to be all most completely to the left. Is there any way to bring the FSB back to vertical with out replacing the barrel or having major smithing work done(in otherwords can I do this myself)? Is there something I should be looking for that would indcate it is out of adjustment or out of wack? What tools do I need to have in order to potentially fix this problem? Thanks in advance for any help you all can provide me. Brian |
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Find a leather type hobby store and pick up a big Leather (wrap type) mallet. Now while holding just the upper receiver, make a blow on the FSB just above the barrel. This will slip the entire barrel in the upper barrel socket, and correct the needed Front sight(barrel) index to allow the rear sight to be centered when zeroed. Note: again, you only want to hold the upper receiver only, and no portion of the barrel. And, you want to make the blow to the FSB to slip the entire barrel in the upper socket with something that will not mar the finish on the FSB, hence the leather mallet. |
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Pull the upper off the lower, set the upper in your lap (Across both legs), hang onto the upper reciever with one hand (pinned against your leg), and make the blows to the FSB with the mallet with your other hands (FSB just past your other leg). The barrel is going to slip in the upper receiver socket long before you even get close to bending the barrel (or breaking your leg). 
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Well after smacking the FSB, I got nowhere.ht By the way this is an old preban rifle with an A1 front and rear sight. The FSB is held on with spring roll pins. It has an Airforce(?) telescopic stock. The gunsmith was impressed that the rifle was still pretty tight as far as fit goes. Brian in Ohio |
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Biting a hole through my lip regarding your smith, The FSB should be installed with taper pins, not roll pins!!!! To prevent having to come back and edit my own post in regards to going way over the top in regards to the COC, post in your hometown forum to see if any one has the tools close to you to pull the barrel. Not that the leather mallet correction does not work, but I want you to see just how much free twisting room that the upper barrel socket slot has to the barrel extension pin with the barrel nut loose. As for reinstalling the barrel correctly indexed, you can pre-position the barrel correctly bore sighted with the centered rear sight via shims (cut from a Pepsi can and position between the barrel extension pin/ upper barrel socket pin slot), or use the leather mallet after tighten the barrel nut (drifting the entire barrel in the upper socket). |
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Dano523, I've seen an A1 upper like Wheatchex1 describes with a FSB installed with roll pins. The rifle belongs to a friend/customer of mine. I was helping him swap upper receivers. He got the rifle used and has no idea who made the barrel. I did question the roll pins. Wheatchex1, I had a Bushmaster barrel with a canted FSB. Bushy offered to fix it, but I decided to fix it myself. I'm sure to the horror of many on this board (  ), I used a file to very slightly open up the barrel pin notch in the upper receiver. I got the barrel where I wanted it and then had to make shims using aluminum from an empty beer can. That was my excuse to have a cold one anyway.  First time I shot the rifle after making the adjustments it was just about dead on at 100 yards. There are a lot of good guys in OH on this board. Dano's advice that you check your Hometown Forum is a very good suggestion. Someone should be able to help you out. Best regards, Mark |
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One one of my rifles, I used the mallet fix becuase the FF tube on the rifle would have been such a PITA to remove. Actually, rather than use a mallet, I held the upper in an upper receiver fixture and used a long screwdriver inserted through the FSB to CAREFULLY rotate the barrel in the upper. Completely fixed the problem. On another of my rifles (with an easier-to-remove FF tube) I fixed the problem properly. To do this, again you need an upper receiver fixture and an armorors barrel wrench. You have to remove the barrel nut as though you are going to remove the barrel; this will reveal the barrel "pin" (actually, a ridge machined in the barrel) and the slot it fits in on the upper receiver. You will see how much (if any) play you have to work with. In my case, it was necessary to slightly file on one side of the slot, align the barrel, and then peen the opposite side of the slot (with a hammer and punch) to ensure a tight fit that did not move when reinstalling the barrel nut. For both the above methods, you need at least an upper receiver fixture. An armorors wrench is always useful. FYI, I have the units below:  
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