Ctc - Ken Waters wrote an excellent article on this very thing years ago in Handloader magazine. I'll be able to locate a copy next week, if you should still need it.
My son and I also have New Service .455's; British purchased during WWI. Both have had the .45 Colt caliber alteration and since .45 Colt brass is readily available (and .455 is not); we use .45 Colt data in moderation with great success.
My son and I also have New Service .455's; British purchased during WWI. Both have had the .45 Colt caliber alteration and since .45 Colt brass is readily available (and .455 is not); we use .45 Colt data in moderation with great success.