Well, the board is either fixed, or it's going to run terribly. Cross your fingers and hope for the best. I'm at my technical limit right now.

AR sights issue?

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S.B.
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AR sights issue?

#1 Post by S.B. » Sat Jul 15, 2017 2:00 pm

when will any including Colt be able to attach fhe front sight tower top dead center, so rear sight apenture will be in center? I mean we live in the age of CNC don't we?
Steve
Last edited by S.B. on Sun Jul 16, 2017 10:54 am, edited 1 time in total.

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Re: AR sights issue?

#2 Post by Ghoulardi » Sat Jul 15, 2017 11:20 pm

everything made in this world isn't going to be perfect, that's why they make sights adjustable.

so how many clicks did you have to move the windgage?
COOL IT WITH THE BOOM-BOOMS!! OVA-DAY!!

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Re: AR sights issue?

#3 Post by RWS » Sun Jul 16, 2017 8:39 am

This is usually a hand-fitting issue, one that can be be solved with patience and the right tools.

Generally, the problem is not with the front sight base being misaligned with the barrel (although that does infrequently occur). The problem is that the alignment pin at the breech end of the barrel goes into a slot at 12 o'clock in the upper receiver barrel threads, and the slot is typically slightly wider than the alignment pin. This allows the entire barrel assembly to rotate back and forth a degree or two.

When the barrel is installed, if there is no provision for ensuring that the barrel alignment pin is centered in the slot then the front sight will be canted slightly to the left (as viewed by the shooter when aiming) because the torque on the barrel nut moves it that direction during tightening.

The result is that the rifle shoots to the right and the rear sight must be moved to the left of center, sometimes as far as it can go.

Ideally, what is needed is a fixture that will hold the front sight base perfectly vertical and the barrel pin centered in the slot while the barrel nut is being tightened. I don't have such a fixture so I use one of the delrin blocks that inserts into the upper receiver and sticks out far enough so that a vise can get a good grip on it. Put some lithium grease only on the forward/leading edge of the barrel abutment upon which the barrel nut bears, and a small dab on the upper receiver threads. Do not put any grease on the part of the barrel that enters the upper receiver, nor any on the interior portion of the upper receiver.

Finger-tighten the barrel nut. Find a helper and insert a 2-foot length of 1/2" dowel rod or broomstick through the big hole in the front sight base. Use this to lever the front sight base into as perfect a vertical alignment as can be eyeballed. Have the helper use the dowel rod to hold against the torquing force of tightening the barrel nut. Check to make sure the barrel itself did not rotate and that the front sight base is still vertical. If it did move, loosen the nut and repeat as often as necessary until perfect alignment is achieved.

If you are stuck with an AR that came to you with the front sight base canted then you can remove the hand guards and gas tube, loosen the nut, re-position the barrel, and re-tighten. Just gotta have a barrel wrench, wooden dowel, and the block for the upper receiver.

-Bob

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Re: AR sights issue?

#4 Post by S.B. » Sun Jul 16, 2017 10:57 am

Bob,is it possible to shim the pin while in it's slot, a few thousandths"?
Steve

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Re: AR sights issue?

#5 Post by RWS » Sun Jul 16, 2017 2:37 pm

Possibly. The pin is very short and very small in diameter so small hands and keen eyesight would be a great advantage as the shim would have to be very, very small.

I've never actually tried shimming one because of how tedious it would be. For me, having someone holding a lever on the front sight base while I torque the nut works well enough. Even then, the rear sight often is not perfectly centered but it is only 2-3 clicks off center. I can live with that.

When I first started building AR's in the early 1980's the first few I built all had front sight bases that leaned slightly to the left (from the shooter's perspective). Eventually I figured out how to keep the front sight from moving (using the wood dowel rod) after it was adjusted as perfectly as possible for vertical alignment but BEFORE the heavy torquing was done that usually caused the barrel to rotate those few degrees.

Just curious, Steve... I'm betting your front sight base appears to tilt to the left when aiming, meaning the rear sight has to be moved way to the left. Is that the case?

-Bob

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Re: AR sights issue?

#6 Post by S.B. » Sun Jul 16, 2017 5:03 pm

Actually, I just screwed another together last week, M4 configuration. Upon shooting for the first time I had to move the rear(plastic) sight to the right several clicks? The only one I've ever seen be close was a military upper I bought in Indianapolis complete with barrel. Sights on this were dead center. Other than my match gun whitch I have a kreiger heavy barrel on with glued(locktited) front sight tower.
Steve

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