Would a canted gas block cause my AR to shoot this much off-center?

[gunsrfun1]

This is a followup on another post, but with more detail. I got a Stag 3H upper awhile back and noticed the front gas block is canted about 1-2 degrees to the right. It doesn't sound like much, but I do notice that when I tilt the upper to get the level centered on the gas block, the rear of the upper does move a bit.
I took it to the range on Sunday, and it was shooting about 5 inches left at 25 yards with the front and rear BUIS centered. I had to run the rear sight almost all the way to the right to get it centered.
The gas block is clamped in place on the barrel by two hex-head screws. I believe I can simply loosen the screws and move the gas block left, unless they are loctited in place or something. The screws are free of the barrel; that is, they are not touching the barrel or any type of channel in the barrel.
My question -- do you think this is the cause of the problem? I don't know much about ARs or ballistics, but would such a small amount of cant produce such a large amount (5 inches) of windage? Having seen how much the rear sight physically moved when I tilted the upper to get the gas block level, it sounds like this could be the issue.
Or -- could it be an entirely different issue. Reason I ask is that I don't want to mess with this forever, I just want it fixed right. But on the other hand, why send it back for something I can probably do myself -- if that is all there is to it.
BTW, other than being off-center, it's pretty accurate. I put a scope on it and was getting about 1/2-inch groups at 50 yards, once I centered the group with the scope. But again, I had to move the cross hairs a bit to get it centered. (I had boresighted it at home.)
Any insight would be appreciated.
Thanks.

 

[stubbicatt]

I don't think so.

The relationship of the sights to the centerline of the bore will affect shot placement relative to your sight picture.

Unless you are using the level you placed on the gas block to align everything.

 

[madcratebuilder]

Front sight canted right well move point of impact left. You need to check the FSB. The gas port in the FSB is larger than the barrel gas port and you have some amount of adjustment or movement.

Remove the FSB, since you have fired the rifler you should have some carbon witness marks on what the current alignment is. You could just loosen the screws and rotate the FSB and hope for the best.

Download this TM and read it. There is a chapter on canted front sights.

http://www.ar15.com/content/manuals/TM9-1005-319-23.pdf

This is the Army TM on maintaining the AR.

 

[gotigers]

You can zero it and it will keep consistant groups at varying distances, but you could run out of windage on your rear sight. That is what happened to one of my ARs. Mine was a pinned FSB. I had to replace it with a clamp on.

 

[awgrizzly]

If the gas block isn't properly aligned on the barrel, besides throwing the sight off, you can have reduced pressure in the gas system and a misaligned gas tube that can cause damage or excessive wear on the rear tip of the gas tube and the gas key. Madcratebuilder's idea of checking the carbon mark around the gas port under the gas block is a good one. It should have loctite on the set screws... use good tools. You can align the gas block by making an index mark for the center of the gas port on the barrel behind the block, and another index mark on the gas block for the center of the gas port there, and then align the two when assembling. Or it would be a simple and hopefully inexpensive task for a gunsmith.

 

[chrome_austex]

Ok, exactly 2 degrees of cant is ~0.0907" of lateral shift at a front sight 2.6" tall.

For a sight radius of 16", 0.09" of deflection is magnified to 5.1" at 25y. So yes, a small degree of cant can throw off mechanical point of aim by that much.

As long as you don't obscure too much of the gas port, you can probably just loosen the clamp screws and adjust it for a bit better alignment, or just compensate with rear sight windage. Either way.