I had the exact same thing happen to me. Tried the cases in a .450 nitro 1902 Webley falling block, a Holland and Holland .450 underlever hammer DR and a Purdey top lever Whitworth barreled .450 3 1/4". Cases would not fit in any of them! I called Hornady and they sent me a new sizing die, still would not work! I went to some old Bell brass and all was well!