I had that problem just recently. I've got a Midwest railed gasblock with the MOE carbine guards and MBUS set. The front sight wouldnt even lock down due to the gasblock being so low. My fix: an extended railed riser from YHM. Its not pretty, but it def. gets the job done until I scrap the cash for a railed handguard. +1 on not attaching it to the MOE guards. They are a great replacement, but not rock-solid.