You got me thinking about the term "step-down crimp" so I pulled-out my copy of Speer Manual #14 and found their discussion on page 751. BUT, they called it a "neckdown crimp". So, maybe my mind messed-up the term, but I THINK that I have seen it called a "step-down crimp" elsewhere. The Speer write-up says
"No special or extras equipment is required if you use Gold Dot bullets and RCBS dies. Rather than rolling the case mouth into the groove, neckdown crimping irons a step at the case mouth that nearly fills the cannelure. ..."
Anyway, try searching for "neckdown crimp" and see if something from Speer comes up.