Our Generation II Expander Dies completely capture the mandrel within the die so the mandrel cannot pull out. An O-ring in the die cap allows the mandrel to float a bit and find its own center within the case neck. All three Generation II dies are precision machined from stainless steel and the 7/8 inch - 14 dies include the Sinclair Stainless Steel Split Lock Ring. Large caliber expander dies accept only 35 to 50 caliber mandrels. All expander mandrels for Sinclair Expander Bodies are sold separately