So to make a long story short, see the following thread HERE

How much windage is too much windage to be acceptable for a zero? I had a old ban era bushmaster deneutered by threading and having a proper bayo lug FSB installed. I get the rifle back together and go to zero it in. The rear sight I never touched from where it was zeroed before. Now after zeroing, the rear sight it almost touching the left of the sight base ears. While it is zeroed now, it bothers me that I lost a lot of windage adjustment. I can understand 2-3 clicks to zero, but if I remember right, I had to crank in 10+ clicks.
So is this too much? Should I live with it or try and have it fixed. I can eyeball it and it almost looks like the FSB is canted to the right just a hair. Not enough to be captured on camera, but you can see with your eyes.

Sorry about the picture quality, my camera has trouble taking pictures of dark things, even with tons of light.

I am no expert and have no actual fact to base it on.  That would bother me too.  I have a couple older A1 type uppers that are similar.  I have reinstalled and torqued the barrels trying to correct it without much success.  I thought it was the barrel index being off just slightly causing a cant on the front sight.  They do zero but like yours it does not leave much room to adjust one way.  I do not like it because for faster shooting the gun does not line up naturally and I have to look for the sights since they are off to one side.  In AK's a zero is acceptable like that.

I only have two pinned FSB barrels (rifle and carbine), but with an A2 and flattop, they've been within 2-3 MOA. Inside the first hash which is 4 MOA for a rifle radius.

That's my standard.

It could be that the new FSB wasn't installed perfectly straight, but it could also be your assembly method (what you used to hold the upper/barrel in place, and if grease was used in the right spots while torquing the barrel nut.

The indexing pin slot on the upper could also be compromised from being damaged by the indexing pin.

How often do you adjust windage while shooting?

For mil spec and rifle zero'd, up to 13 clicks off center is acceptable.

Have you considered just removing the special aperture hood?

Following this thread as I have a similar problem. I installed an M4 barrel in my A2 carbine

Before

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After

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Now the rear sight is close to max on the left and it bother the hell out of me. I guess the Colt barrel I bought had the front sight canted

Attached File

Check index pin slot slop at receiver nose. Also feedramp alignment with cuts in receiever (if ramped).

Your bbls may be rotated due to torque and excess play in the pin/slot.

To answer a couple questions. The barrel and old rear sight were lined up perfectly before as I am about 99.9% sure it was still factory assembled and had never been touched.
Upon reassembly, the barrel to receiver fit was very nice and snug with no play. The index pin and slot had zero play, and in fact I had to give it a good tug to get it out when removing the barrel, and a good push to reinstall it. So the index pin and slot are a nice tight fit. As far as feed ramp alignment, this barrel has a rifle extension and carry handle upper, so no feed ramps in the receiver.
I did use grease on the barrel nut threads. I used a wheeler delta series vice block kit and a magpul armorers wrench to disassemble and reassemble.

Then it is 1 of 2 things....

Either the index pin slot is cut off center on your upper ( slim chance).

OR your FSB was pinned out of alignment (canted).

That would bother me.

I had an issue M-16-A2 that was 8-9 clicks L windage to get zero at 200 meters. It was a bitch when fighting the wind at 500 meters...

Range coach and the armorer said "deal with it, it's in-spec."...

Lots of front sight error can be fixed with a good rear site. For example If we look above at the photo of OLIAR15's rear site. Close examination seems like the casting was poor, the center of the site is not in the center of the receiver, it also seems canted some all of which are showing up in the error direction. Plus every A2 rear site deserves an ear tit and a wheel shim.

When I build an upper if the rear site is not going to get pinned I like to weld a tit on the ejection side ear at the bottom then file and fit it so the ears are parallel with the receiver, this will also take out some of the front to rear play. If the receiver is straight it will track well. A site wheel shim kit can also have a positive impact on site track up and down which is crucial for an accurate mechanical site. A machined base is highly superior, a genuine military base is the next best, and commercial reproductions are not held in high favor for accuracy.

I love the A2 rear site, it is the ultimate evolution of the analog military site.

ETA: Sorry to rip on your site @OLIAR15 !! IM me your street addy and I'll send you a colt take off.

I have a colt model 6551 that was off 14 clicks, that was terrible, I sent it to Bushmaster and they took upper apart and when I received it back it zeroed dead center, I was so happy. This was 20 years ago. In my opinion I wouldn't be happy with any that had to be over more than 4 clicks.

Thanks, no need to be sorry, I am looking for a solution. If anything I am sorry to crash the thread of Jeeps-and-Guns..

You’re probably right, my rear sight may be suspect, although the whole rifle is an original Colt. And it was already somewhat off to the left with the original barrel, it just got worse with the replacement barrel.

What is an ear tit and a wheel shim ?

Thanks for your guidance and generous offer.

An ear tit is a bump on the front of the sight housing that presses against the receiver to rotate the housing so the gap (looking down at the sight) is even.

Wheel shim tightens play in the elevation drum.