This is an RCBS Cowboy 3 Die Set for the 38-40 Winchester caliber. RCBS Cowbooy Dies are built to slightly different dimesnsions than their regular dies to allow optimum sizing expanding, seating and crimping needed to load great lead bullet ammo for Cowboy Action shooters of lever-action and single-action revolvers. Uses shell holders RCBS #35 or Lyman #7.