An infusion pump assembly includes a locking tab and a pump barrel inside a pump barrel housing, where the pump barrel accommodates a reservoir assembly. The reservoir assembly includes a reservoir and a plunger rod. The infusion pump assembly also includes a locking disc at a terminus of the pump barrel. The locking disc includes a clearance hole for the plunger rod. The locking disc also includes at least one locking tab notch in close proximity with the locking tab. The locking tab is in movable engagement with the locking tab notch, and the reservoir moves the locking tab from a locked position to an unlocked position when the plunger rod is inserted through clearance hole. The locking disc rotates upon torque being applied to the reservoir assembly, the locking disc rotating from a non-loaded position to a loaded position with respect to the plunger rod and a drive screw.