A dynamic shaft seal assembly is provided including a dynamic seal for engaging a rotary shaft. The dynamic seal includes a mounting portion that is mounted within a casing and has an axially extending barrel portion extending from a radially inner end of the mounting portion. The axially extending barrel portion terminates in a radially extending leg portion which extends inwardly from an end of the axially extending portion. A generally conically shaped seal portion extends from an end of the radially extending portion and the seal portion includes a radially inner face engaging the shaft and a radially outer face having a stiffening bead integrally formed thereon. The mounting portion defines a bumper spaced from the axially extending barrel portion by a gap distance that is designed to prevent the seal lip from inverting under sustained high pressure or pressure spikes.