I have a 14.5" AR15 with a SIG Romeo 8T which is a wonderful optic for the rifle. I decided to get a magnifier to put behind it (selected the Vortex 3x). Its great except the rear lens cap for the Romeo 8T won't open all the way because the magnifier is in the way. So I tried moving the Romeo 8T forward but that causes it to bridge the receiver and hand guard (I understand this is a bad thing). Then I got a ARMS rail. Which allows the optic to be moved forward slightly but then the magnifier's QD mount for whatever reason won't attach to the ARMS rail. I'm not sure the best way forward on this one so that I can keep the magnifier on the rifle and the rear lens cap won't fowl when opening on the magnifier.