Gunsmithing AR-15 Iron sight help needed

[TresMon]

Hiya guys,

I got an AR-15 from an old gent that want's me to fix the sights. He wants to shoot it with the iron sights. It's a straight up A2.

Anywho his complaint is that for the rifle to be zero'd the rear sight has to be almost maxed out to the left for it to be poa/poi @ 100. He wants the rear sight mostly centered & the rifle zero'd.

I checked the indexing pin on the barrel @ the receiver etc- everything looks right.
What to do?

Thanks.

 

[mheckman]

Re: AR-15 Iron sight help needed

I have seen a few barrels having their front sight base taper pins not perpendicular to the indexing pin. One solution would be to install a windage adjustable front sight base. I use them on all my AR across the course rifles for highpower competitions. It involves milling two flats on the barrel for the horizontal adjustment screws.

 

[Redmanss]

Re: AR-15 Iron sight help needed

When we would encounter a M16A2 with excessive windage on the ranges at Parris Island, the 2111 Armorer would mount the upper in a vise, set up a bore sight target, and use a prybar to flex the carrying handle/sight assembly in the proper direction to bring it back in line.

I know there are quite a few of you cringing over that, but it worked.

Have you checked it on a bore sight or the range yet? Just wondering out loud here....

 

[Outsydlooknin75]

Re: AR-15 Iron sight help needed

Tres, what I would do if it were me is I would pull the barrel and see how tight the index pin is in the upper. If need be I would make the adjustments there, open the notch in the upper just slightly and shim one side or the other to rotate the FSB in the direction needed. It might take a while to get the rear centered but it would be the easier and least expensive way to do it (other than test firing after each adjustment).

 

[TresMon]

Re: AR-15 Iron sight help needed


Thanks guys.

All good comments!

 

[ThomasA]

Re: AR-15 Iron sight help needed

I have seen canted FSB's before. The FSB can be out of spec, or the taper pin cuts, or barrel extension were machined/installed incorrectly. You could just put on a clamp-on FSB. He might enjoy a folding one?

 

[TresMon]

Re: AR-15 Iron sight help needed


ThomasA,

Yeah, if nothing else works, i.e. cheap fixes, I'll move to a set screw FSB.

Thanks,
T

 

[wnroscoe]

Re: AR-15 Iron sight help needed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Redmanss</div><div class="ubbcode-body">the 2111 Armorer would mount the upper in a vise, set up a bore sight target, and use a prybar to flex the carrying handle/sight assembly in the proper direction to bring it back in line.</div></div>

Damn Jar Heads. Thats why all the shinny stuff gets stowed away when marines come aboard a Navy ship

JK guys, dont flame me too bad.

 

[Redmanss]

Re: AR-15 Iron sight help needed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Redmanss</div><div class="ubbcode-body">the 2111 Armorer would mount the upper in a vise, set up a bore sight target, and use a prybar to flex the carrying handle/sight assembly in the proper direction to bring it back in line.</div></div>

Damn Jar Heads. Thats why all the shinny stuff gets stowed away when marines come aboard a Navy ship

JK guys, dont flame me too bad.</div></div> Give a Marine grunt two ball bearings, lock him in a padded room, and when you come back 30 minutes later he will have broken one and lost the other!

 

[TresMon]

Re: AR-15 Iron sight help needed

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Outsy</div><div class="ubbcode-body">Tres, what I would do if it were me is I would pull the barrel and see how tight the index pin is in the upper. If need be I would make the adjustments there, open the notch in the upper just slightly and shim one side or the other to rotate the FSB in the direction needed. It might take a while to get the rear centered but it would be the easier and least expensive way to do it (other than test firing after each adjustment). </div></div>

Would making a flat on the index pin do the same thing? I think yes- but would this reindexing of the barrel/extension screw with the bolt going into battery?

 

[TresMon]

Re: AR-15 Iron sight help needed



Fixed!

Ground .025" off one side of the barrel indexing pin. I shimmed the other side the same amount and now the rifle is zero'd with the sights centered,

Thanks eveybody.