Okay gentlemen. After the prerequisite search, I was unable to find an answer to my problem. So, I will ask directly. When I built my AR I put a folding front sight on a railed gasblock. When sighting in the iron sights I had a problem. I was unable to screw the front sight post in (down) far enough to pull my shots up onto the bulls eye at 25 yards. I had to use the elevation wheel on the removable carry handle rear sight to get enough elevation to place the shots on in the bulls eye. If it had been 1 or 1 ½ inches then no big deal. But I’m talking about 3 inches at 25 yards. Right now the elevation wheel on the rear sight is on the 4. I have a DPMS gas block rail. I went cheap on the front sight and bought an NCSTAR folding front sight. My questions to you are these. 1. Are all gas block rails the same height and should that height match the height of the rail on the upper? ( this one is a quarter inch lower than the rail on the upper and I imagine that the rounds would have been in the ground if the gas block rail matched the upper) 2. Can I file down the front sight post to get the last little bit of adjustment? 3. Is it better to buy a “matching set” of BUIS? 4. Should BUIS be mounted on the same plane? Thank you in advance for any help you can provide. Vince (EDIT) Thanks for looking but I did another search and found that someone had the same problem back in 2009. I now know what to do.