I have a BM upper with the standard fsb.  It seems to be canted to the right slightly.  When I put my red dot (zeroed) on and co-witness the dot appears to be on the right corner of the sight post.  Does this make since?  How do I fix this?  It bugs the hell out of me.  I've adjusted my arms #40 quite a bit to the right to zero.  The gun functions fine, and some would say leave it alone.  I just don't like it.  I would appreciate any helpful advice.

Thank you

I could be that the front sight is canted in relation to the index pin on the barrel extension, or it could be that the index slot in the upper receiver is off.  With the bolt in the carrier, slowly move bolt in and out of the barrel lugs to see if there is any more clearance on one side or the other.  If you have enough clearance on the right side, you could open up the index slot a little and rotate the barrel counter-clockwise (looking from rear to front) to get the front sight to align with the upper.

I had a BM 16" that I though had a canted front sight, but when I replaced the barrel with a 20", I found that my windage was still off roughly the same amount.  At this point, I am pretty sure it is the index slot on my upper that is off.

Yes I have zeroed the irons.  I can shoot well enough (2.5" group @ 100m) with the way it is now.  I just know that it is not right.  Am I making since?

Sorry Guys - I'm confused the rear sight (#40) doesn't seem to be off by that many clicks (8).  It is a 16" bbl.  I'm still confused.  I have a good zero with my Burris Speed Dot, and my irons.  The 4moa dot is obviously on the left hand corner of the front sight post while co witnessing.  I don't get it.  Both optic and irons have been zeroed nicely?  I never use them together though.  It doesn't seem practical.  It gets to busy trying to look through the rear iron, the red dot, the fs, and the target.