You may find your barrel slugs near .454 - if so, it's a good day for you. Load .454 and watch the targets fall. .454 might cast .455 which would also work for you. Check your barrel before you get too concerned. You may have a match, just not at the "new" diameter, but at the "old" diameter. You will have to make sure you have .454 loading dies, not .452 - good luck and keep us tuned in.