A method of locking a handguard relative to an upper receiver of a firearm. The method includes providing a wedge assembly having a top wedge member and a bottom wedge member, each having complementary inclined surfaces; a barrel nut that is configured to receive an outer portion of an upper receiver; and a handguard that is configured to receive the barrel nut and the combined wedge assembly within a lower lip of the handguard. The wedge assembly may include an optional assembly screw and a locator pin where the top wedge member and bottom wedge member are tightly joined to each other via the assembly screw and the locator pin. In use, the lock-up system is used to join the handguard and barrel nut to a corresponding upper receiver with little to no play between the handguard and the upper receiver such that the connection between the two via the wedge assembly is intended to be permanent.