AR Rear Sight Question

[Misery Loves Shotguns]

My wife's AR15 needed to be rezeroed because the barrel nut came loose and I just got it back out to shoot today. It seems to be shooting a few inches to the right at 50 yards. I benchrest it, hold dead center, breathe and squeeze and it took quite a lot of windage adjustment to get it shooting to point of aim. It has a Magpul MBUS rear sight, we leave the arperture up all the time and I'm wondering if there's something wrong with the sight. I was zeroing her red dot to cowitness the iron sights today and what I should have done was shoot with the rear sight down and then up and see if the POI/POA changed. Didn't think about it at the time. Anyway, for those of you who've been at this rifle business a lot longer than me, is it normal to need to drastically adjust the windage to zero? I thought it was odd because the sight has a center mark on it and I'm WAY over.

[Misery Loves Shotguns]

This fellow seemed to have the same problem ...

https://www.youtube.com/watch?v=-OaFG_k95n4

[danhr]

Pretty normal. Depends on the shooter and the rifle. Especially if you switch between left hand shooters and right hand shooters. I remember sometimes in the military, I had to crank the rear sight damn near all the way to one side.

IMO, a more important question would be, why are you zeroing your wife's rifle and not her. Her zero isn't going to be the same as your zero.

[Gunsnwater]

Shooting the loose barrel may have damaged the slot in the upper for the indexing pin in the barrel extension. Look for a canted front sight.

[ianb1116]

Is it normal? No. Does it happen? Yes. If you've got it zero'd I wouldn't worry too much if it holds.

[dkf]

If the FSB is canted you can require a lot of windage on the rear to line things up. Its not uncommon for the front of the upper receiver that the BE seats against to not be square to the bore. If it is severe you may get a cant. But usually the front sight position is the culprit.

[arjohnson]

Possibly you over torqued it and the front sight base is now canted.

[mpan72]

Was it very windy while you were shooting?

[Hawk]

It's pure luck to have a "off the shelf" AR zeroed and have the rear sight in the center of the windage marks. To achieve it, if you are unlucky, you need to either re-index the barrel in the upper or install and adjustable FSB. I've seen guys widen the indexing slot on the upper so they could rotate the barrel slightly to compensate for having to dial on too much windage. Many Match Grade AR's have adjustable FSB that permit you to zero your rifle and have the rear sight base exactly centered in the windage hash marks.

Personally, I don't let the sight being to one side when zeroed bother me on AR's that I don't compete with.

[arjohnson]

It's pure luck to have a "off the shelf" AR zeroed and have the rear sight in the center of the windage marks. To achieve it, if you are unlucky, you need to either re-index the barrel in the upper or install and adjustable FSB. I've seen guys widen the indexing slot on the upper so they could rotate the barrel slightly to compensate for having to dial on too much windage. Many Match Grade AR's have adjustable FSB that permit you to zero your rifle and have the rear sight base exactly centered in the windage hash marks.

Personally, I don't let the sight being to one side when zeroed bother me on AR's that I don't compete with.

I think it's something like 10 clicks either way and it meets spec.