Hello Blind-Eye ;

 Looks to be a repro of the old , very old, style breech seating tool from yesteryear.

 Is that an engagement lug that I see just rearward of the head of the brass case ?  I don't recall ever seeing an engagement lug on these style bullet seating tools, but would be most interested in learning from you how that might work.

 Thanks much,

 Creedmoormatch