An apparatus for sealing a puncture extending through tissue, comprising: an elongate member comprising a proximal end, a distal end sized for insertion into a puncture through tissue, and an expandable member on the distal end; a cartridge comprising a proximal end, a distal end sized for insertion into the puncture, and a lumen extending between the proximal and distal ends (122, 124) sized for receiving the elongate member therein; a sealant disposed within the cartridge lumen adjacent the cartridge distal end; a pusher member disposed within the cartridge lumen adjacent to the sealant; and a tamping device on the cartridge proximal end for biasing the pusher member distally relative to the sealant when activated, wherein the cartridge is movable along the elongate member from a proximal position wherein the cartridge is disposed adjacent the elongate member proximal end to a distal position wherein the sealant is disposed adjacent the expandable member and the tamping device is activatable to bias the pusher member to move distally to push the sealant towards the expandable member, the apparatus further comprising: a cartridge hub on the cartridge proximal end for directing the cartridge from the proximal position to the distal position, the cartridge hub comprising the tamping device therein, wherein the cartridge hub is slidably coupled to the cartridge proximal end, characterised by the tamping device comprising a slider member within the cartridge hub fixedly coupled to the cartridge proximal end and a spring member coupled to a proximal end of the pusher member, the slider member biased to a first position within the cartridge hub such that the slider member moves distally with the cartridge hub when the cartridge is advanced towards the distal position, and wherein the slider member moves proximally within the cartridge hub to a second position when the cartridge cannot be advanced further to the distal position, so that the bias of the slider member to the first position is overcome, thereby compressing the spring member to bias the pusher member to move distally. an elongate member comprising a proximal end, a distal end sized for insertion into a puncture through tissue, and an expandable member on the distal end; a cartridge comprising a proximal end, a distal end sized for insertion into the puncture, and a lumen extending between the proximal and distal ends (122, 124) sized for receiving the elongate member therein; a sealant disposed within the cartridge lumen adjacent the cartridge distal end; a pusher member disposed within the cartridge lumen adjacent to the sealant; and a tamping device on the cartridge proximal end for biasing the pusher member distally relative to the sealant when activated, wherein the cartridge is movable along the elongate member from a proximal position wherein the cartridge is disposed adjacent the elongate member proximal end to a distal position wherein the sealant is disposed adjacent the expandable member and the tamping device is activatable to bias the pusher member to move distally to push the sealant towards the expandable member, the apparatus further comprising: a cartridge hub on the cartridge proximal end for directing the cartridge from the proximal position to the distal position, the cartridge hub comprising the tamping device therein, wherein the cartridge hub is slidably coupled to the cartridge proximal end, characterised by the tamping device comprising a slider member within the cartridge hub fixedly coupled to the cartridge proximal end and a spring member coupled to a proximal end of the pusher member, the slider member biased to a first position within the cartridge hub such that the slider member moves distally with the cartridge hub when the cartridge is advanced towards the distal position, and wherein the slider member moves proximally within the cartridge hub to a second position when the cartridge cannot be advanced further to the distal position, so that the bias of the slider member to the first position is overcome, thereby compressing the spring member to bias the pusher member to move distally.