First off, I am new to join although I have been visiting this site for some time now and it is far and above any other for quality content and ADULTS. I just recieved a new 14.5" midlength upper from BCM. I coupled that with a S&W M&P lower with a DD parts kit. I put on a Magpul flip up rear sight. When I took it out to zero my rear sight needed to be adjusted almost all the way to the left to get on target. I e-mailed BCM and they blew it off as if it was a non issue. My question is, should I be at all concerned about this? It seems it will be an issue for co-witness if nothing else. Is there some fix for this? Any imput would be greatly appreciated. By the way as you may have assumed I am relatively new to the AR platform. I have owned only Ohio legal hunting weapons until I purchased a DPMS sportical this past spring (laugh here!). However after research on this site I moved up. I think.