A dual mode pistol grip grease gun that operates in either the volume mode or the pressure mode. The grease gun includes a cylinder head having a handle attached thereto. Attached to the cylinder head via a shiftable link is a lever, which has a slot at one end. The shiftable link is disposed in the slot of the lever, and its position therein defines whether the grease gun is in the volume or the pressure mode. The shape of the slot is such that, when the grease gun is in volume mode and when the lever is fully pressed toward the handle, an angle defined by a first axis (defined as a line connecting a pivot point of a connection of the link to the cylinder head and a pivot point of a connection of the link to an end of the slot defining volume mode) and a second axis (defined as a line connecting the pivot point of the connection of the link to the end of the slot defining volume mode and a point along a bottom curve of the slot where the concavity of the curve changes) is approximately ten degrees. The shape of the slot, roller and tabs on the link allow for ease of shifting.