I posted a CAUTIONARY above (way above) about a Mag Tube plug that screws into the Mag Tube. If marginally rusted, or installed by Bongo, Uberti's resident Gorilla, removal of the threaded plug may be some difficult. Also, the tube may well turn in it's mounts and ferules which will cause the locator cross pins to make grooves in the tube causing the Follower to bind.
Important to CAREFULLY place the tube in a padded vice to prevent the tube from turning with the torque applied. Also, once a threaded Magazine Plug is out, after a thorough cleaning, the threads should be coated with an anti-seize lubricant before install.