Levers, just measured a few different 45/75wcf cartridges that are loaded with bullets cast from an original Winchester mold , and the bullets are on the + side of .458" as cast. The same bullets loaded into brass formed from 50/90 Sharps to 45/75wcf measure .011" neck thickness per side. Jammison brass that I have measure about the same + or minus a 10 th or two. The neck OD of a loaded cartridge with said bullet measures about .481" to .482" . These loaded 45/75 wcf cartridges feed and eject easy through my two original 3rd model 1876 Winchesters. They have a semi roll crimp and are loaded with an original Winchester tong tool. The are very accurate in the old rifles WITH bp.. How do these measurements stack-up with yours. By your sr# you have a early rifle , the early rifles I have measured seem to have tight chambers in the 45/75 and 45/60 . Do you have 5 groove rifling ? Good luck with getting the old rifle shooting . It is a Cool one. If I can help any way just give me a holler,,,,,,DT