An automatic tissue sampling apparatus for use with a biopsy needle set includes a housing defining a cavity and a forward end opening for passage of an inner needle and outer cannula. Two carriers are slidably disposed within the cavity and are configured to support one of the inner needle and the outer cannula. Springs operably engage each carrier and have a cocked position to store potential energy and a firing position to releases the potential energy and drive the corresponding carrier toward the forward end of the housing. A single-handed cocking mechanism, operable to sequentially move the each driving mechanism to its respective cocked position, includes a manually operated cocking lever positioned outside the housing. A force transmission mechanism operably coupled between the cocking lever and the carriers is configured so that the force required to manually depress the cocking lever does not increase as the springs are compressed.