I'd like to install one of those fancy machined handguards with the Picatinny rail along the top to one of my phantom AR-type rifles. The original barrel nut is toothed, and the gas tube through the teeth is what keeps the nut tight. These new handguards have a barrel nut that doesn't look to have any teeth to prevent loosening of the nut. What keeps the nut tight? If it's just friction, that doesn't seem to me like it's going to work for too awful long...