When I bought my Colt 6920 it already had a Matech 600 rear sight installed. I attempted to remove it this afternoon and the lock screw wouldn't move and head felt like it started to strip so I stopped the attempt. My question is does this rear sight take a special tool to install and remove. The lock screw looks like a torqz screw (forgive spelling) or an allen head and neaither seems to work, I don't want to damage it. I appreciate any help.