Numrich gun parts corp. was the source of the old Savage model 340 schematic.

FWIW - I searched their site and they appear to have the Savage band & screw in stock, but, not the special nut.

I have no idea of the dimensions of the Savage parts. I just always thought they had a good idea for a barrel-band, that was discrete and could be put on without removing the front sight.

A handy person could build a variation on such a band. I like Dick Hosmer's idea for trapping the nut.

A 'quick-detachable' swivel-screw, of the machine-screw variety, would be a nice anchor screw for such a barrel-band.