A medicament delivery device includes a housing having proximal and distal ends; a hollow piston plunger within the housing; a telescopic dose drum concentric between the housing and the plunger; and a plunger driver to drive the plunger toward the proximal end having a hollow drive drum sleeve movable within and coupleable to the piston plunger and fixed to the dose drum; an actuator operably connected to the drive drum sleeve; and a stop body for inhibiting rotation of the dose drum and drive drum sleeve when a set dose equals a remaining dose in a medicament container. The drive drum sleeve and piston plunger are operatively coupled such that axial movement of the actuator toward the proximal end forces the drive drum sleeve and piston plunger to couple, whereby the piston plunger and dose drum are displaced toward the proximal end for delivering the set dose.