Got my Bushy, M1S, Ameetec mongral out today and took it to the range. When I got to the range, I noticed the the rear sight housing (A2) was canted to the left. It is  Bushy A2 upper that I have installed a M1S barrel and front sight assy on. (long story) So I twisted it back straight and it springs back to the left cant. OK I can live with that. Now here is kick in the pants. I sighted in my Hakko that I have mounted on a First Samco M44 hand guard. No movement BTW. I then moved to the iron sights. I was shooting WAY to the left with the rear sight canted to the left. So I move the windage adjustment to the right and the I don't think the POI changed. But I just realized that I moved the rear sight the wrong way.

Anyway, why is the rear sight housing being canteed under spring pressue to the left. My Colt preban sure doesn't do this.

My Bushmaster A2 rear sight also springs to the left, to slightly left of center. However, I've had no problem zeroing or holding zero.

The rear sight housing has only a single detent (ball)/spring that pushes on the left side of the upper sight housing track.  This makes the rear sight-housing track only the right side of the upper's housing track.

The canting of the rear sight housing on the upper is normal, and depending on amount of play between the upper tracks/housing, the twisting effect will vary.

The reason for this design is to allow the rear sight to take a hit, and to allow the housing to track true up the right track as it is raised and lowered for the different POI/POA ranges.