Hull

From GunCounter

The shotgun equivalent to a Case. The part of a Shell that ties everything else together: It holds the Primer in proper alignment with the firing pin, protects the Powder until ignition, and contains the expanding gases of the ignited powder and channels it to propel the Shot or Slug down the barrel.

Modern hulls usually consist of a brass lower portion that holds the Primer and Powder, an a plastic tube upper that holds the Wad and Shot (or the Slug depending on the type of Shell). The top is them crimped down to hold the load in and protect it from the elements until firing.

Other materials that have been used for hulls are paper and all brass.