I need help with the following situation. I have been slowly building my Ar15 which consists of a pre-ban Colt lower with a new 16" Stag upper. I would like to remove the rear sight/handle and replace it with a flip-up rear sight, eventually adding an aimpoint (co-witness). Now to my question. If don't replace the standard front FSB with a flip up will it always be in the way when I use the aimpoint. I don't mind changing it but will have to do more research (something to do with the gas block). Any help would be greatly appreciated, I have not ordered anything yet until I clear up this issue.