A downhole tool actuator includes a housing defining an axial bore and a first port extending radially from the axial bore, as well as a piston disposed and movable within the axial bore of the housing. The piston includes a receptacle wall, a shaft extending axially from the receptacle wall, and a contact member extending across the shaft. The receptacle wall defines a chamber and a second port extending radially from the chamber. The contact member is positioned outside of the housing and is configured to engage a downhole tool.