My Gunsmith recommended I don't use the Magazine Tube for as an attachment point for my upper sling swivel. He is concerned that the stress on the tube will loosen it and that it may affect accuracy as well.
Actually where you have the mount is probably just fine. It is very close to a stabilized section of the mag tube and forend.. I only agree with the gunsmith that maybe moving it out further toward the muzzle where it isn't well supported would be a bad idea.
Got my 464 back from the Gunsmith. Said it is shooting ok for him. Back to the range to see if tightening up the magazine tube corrected my accuracy problem.
Bill