Yup. The way you posed your question presumes Ruger would waste time and money holding a non-critical dimension to tolerances as tight as needed for head space. I don't know if they do or not, but the gap behind a .45 ACP only cylinder could vary quite a bit and make no difference while firing the revolver. Even if Ruger held that gap to tight tolerances, the tolerances you give to your machinist co-worker get add together with Ruger's probably accumulating to a wider range than is allowable for head space. I would rather see you spend a little time and be sure you get your head space correct.