The .45 ACP revos formerly headspaced on either the case mouth or with the half moon and full moon clips. S&W then made an engineering decision to deepen the chambers. That probably eliminated a problem with chambering cases of excess length, while creating the problem of excess chamber length for normal cases. One possible cure for those who don't want to use clips at the range is to install a longer firing pin. Cylinder and Slide shop makes one. It works to reach the primers on short cases headspacing on the case mouth.