Probably the 475 No.2 .483" regulated for 480 gn bullet.
(as opposed to the (475 No.2 Jeffery .488" which was regulated for a 500gn bullet).

As you said, one of the rarer calibres.

Re the shallow grooves, some of my guns have very shallow rifling and it's not from shooting them !!!

It seems different makers had different depth of rifling.