I have a WR 1869 in 500/450No.1 express and have found the Bertram brass to be just fine in that gun.
Seems like working with 475No.2 brass would be time consuming and expensive.
I have used the thin copper jacket 350 grain Hawk in that gun and in a 500/450 No.2 chambered Farquharson and they both shoot great. Both have Henry rifling and not Metford though.