An adjustable stock assembly for a firearm, the stock comprising: a longitudinal axis; a chassis comprising a main body configured for mounting a receiver and an axially elongated rear mounting extension extending rearwardly from the main body; a butt pad assembly slideably coupled to the rear mounting extension, the butt pad assembly slideable between a plurality of axial positions on the rear mounting extension for adjusting a length of pull of the firearm; a cheek rest slideably coupled to the rear mounting extension, the cheek rest slideable between a plurality of vertical positions on the rear extension; and a locking mechanism coupled to the rear mounting extension and changeable between a locked and unlocked position, the locking mechanism configured to simultaneously lock both the butt pad assembly in one of the axial positions and the cheek rest in one of the vertical positions respectively; wherein the butt pad assembly includes an axially extending forward adjustment rail slideably inserted into a longitudinal cavity of the rear mounting extension of the chassis; wherein the locking mechanism comprises a pair of clamping blocks biased apart by a spring, the clamping blocks movable together to clampingly engage the adjustment rail of the butt pad assembly to lock the butt pad assembly in axial position when the locking mechanism is in the locked position; characterised in that a first one of the clamping blocks has a first portion engageable with one of a pair of lateral sides of the mounting extension of the chassis, and a second one of the clamping blocks has a second raised portion insertable through a lateral window of the mounting extension for engaging the adjustment rail of the butt pad assembly. a longitudinal axis; a chassis comprising a main body configured for mounting a receiver and an axially elongated rear mounting extension extending rearwardly from the main body; a butt pad assembly slideably coupled to the rear mounting extension, the butt pad assembly slideable between a plurality of axial positions on the rear mounting extension for adjusting a length of pull of the firearm; a cheek rest slideably coupled to the rear mounting extension, the cheek rest slideable between a plurality of vertical positions on the rear extension; and a locking mechanism coupled to the rear mounting extension and changeable between a locked and unlocked position, the locking mechanism configured to simultaneously lock both the butt pad assembly in one of the axial positions and the cheek rest in one of the vertical positions respectively; wherein the butt pad assembly includes an axially extending forward adjustment rail slideably inserted into a longitudinal cavity of the rear mounting extension of the chassis; wherein the locking mechanism comprises a pair of clamping blocks biased apart by a spring, the clamping blocks movable together to clampingly engage the adjustment rail of the butt pad assembly to lock the butt pad assembly in axial position when the locking mechanism is in the locked position; characterised in that a first one of the clamping blocks has a first portion engageable with one of a pair of lateral sides of the mounting extension of the chassis, and a second one of the clamping blocks has a second raised portion insertable through a lateral window of the mounting extension for engaging the adjustment rail of the butt pad assembly.