I recently purchased a new SIG M400 AR and put on a magpul BUIS, but kept the front post on. So naturally I want to sight the irons in before I get a red dot, but I just simply can't do it. In order to sight in you have to get a grouping to move around. I cant get anything even close to a group. heck, @ 50yds I'm not even on the paper half of the time. I'd swear I'm in the correct sight position, and I'm not anticipating recoil. So does anybody know what I could possibly be doing wrong, and how I could fix it?