Like the subject says, I got a magpul mbus flip up set and installed them no problem, took it to the range and couldn't hit the broad side of a barn at 50 yards.... I did have the front post mounted to a railed gas block, could that have been my problem?? I have since purchased and installed a blackhawk quad rail carbine length forend, that appears to be exactly even with the rail on my upper receiver. My second question is, should I now be able to re-install the mbus magpul I have on that quad rail and be golden or will I still have problems?? Thanks in advance.