For shotguns and double-barreled shotguns. A small box holds 20.

—Quake 1 Manual

In Quake, Shells come in two types of Boxes: Small and Large. Small Boxes contain 20 Shells while Large Boxes contain 40 Shells. Grunts will drop 5 Shells when they die. Due to a texture error, there are white lines visible on the bottom of the Large Box.