That actually cleared things up for me. Sounds like if I wanted to make cores in the enlarged area it would work. The 5/8" long smaller dia would be the upward stop for the piston when mounted upside down. Figure some math now. I wonder, if it is running about .040 larger and I wanted a core around .284 maybe the .243 sizer whould do it.
.284 would be a good size core for me to seat in a sized down .223 case for a brass jacket.338 bullet.
This idea my be starting to take shape now. Thanks for your time 454.
Brian