AR Front/Rear Sight Alignment Issues

[4 Brigada]

Took my rifle out to the range first time, tried sighting it in at 25 yards using the M16A1 zero targets (using L sight) with the sight centered point of aim (POA)and point of impact (POI) were off. Point of impact was 3 3/4 in to the left. Adjusted rear sight close to full right to get POA and POI to coincide. Wind gusting about 7mph from 5 o'clock, no noticeable effect at that range. Great groups.
Any ideas on solving this, trying to keep the rifle as original as possible. Any gunsmith that can help?

[supersonic]

Sounds like your FS could be canted. If it's a bolt/set-screw-type gas block, you can just 'eyeball' it until you get it right. If it's a standard taper pin FSB (and it is, indeed, canted) - unless it's still under warranty- the indexing slot where the BBL extension meets the upper receiver will need to be 'tweaked' a bit.

[ar15barrels]

I have found that there are three reasons for canted sights, poor installation job that does not account for sight alignment, a bad front sight installation on the barrel or the index pin cut on the receiver is not centered.

The fix depends on finding the problem.

If it's poor installation, rebuiding the upper is the fix.
It's quite possible to align the sight to the left side or to the right side of the available slop between the barrel and reciever.
This is usually enough to fix alignment in most cases.

In more extreme cases, I have milled out the index pin slot in the reciever and shimmed the index pin on one side to remove all the slop that was created by milling.

I have also removed the taper pins, installed the barrel and sight in my front sight base drilling fixture and re-drilled for oversized taper pins to correct for a poor sight installation.

[supersonic]

In more extreme cases, I have milled out the index pin slot in the reciever and shimmed the index pin on one side to remove all the slop that was created by milling.

I've done a few myself. Except that I don't have a mill. Had to make do with a file & emery cloth.

[4 Brigada]

Thanks Randall and supersonic, Its way off (well to me anyway). Beyond my tool and AR experience capabilities. Dont want to fubar it. Any chance you can fix it, if I send it to you , how is your workload? Randall

[ar15barrels]

Thanks Randall and supersonic, Its way off (well to me anyway).

how many degrees is it off?
How far off center (inches measurement) is the rear sight in order to properly zero?

[4 Brigada]

Well at MK I Eyeball rear sight zero (same number of threads on both sides) at 25 meters it was grouping 3 3/4 inches left with POA at center of mass on a 25 meter M16A1 zero target. The rear sight travel is maxed out to the right to make POA and POI coincide. Its against the right side of the carring handle.

Added Later

From center the rear sight is 0.115 inches to the right to coincide POA and POI. No more right travel is possible.