Not to give hope where perhaps none is due, BUT, by any chance do you think that Lancaster has one of their famous oval-bore barrels or a Metford and not a shot-out Enfield bore?

If it is, you'll probably have to cast for it (see Accurate Moulds; sorry for the plug, [admins. please remove if inappropriate], no relation, just a many-time satisfied client), as I had to do with all of my old #1 Pattern H.L.S.R.s.(largest 0.318)