Nitro cards are used as a seal between the powder and the shot. They can be used in place of a plastic shotcup in European-style loads. Modern load designs use nitro card wads within a shotcup for managing space. Nitro card wads are constructed of a specilized material selected to withstand the tortures of slow-burning powders and heavy payloads.
This size fits perfectly in the bottom of a 12 gauge wad cup to bring shot level up for good crimps. Great for 3/4 oz. loads in straight wall cases to avoid crimp dishing.