An apparatus for sealing a puncture includes a cartridge, a pusher member, a sealant, and a tamping device on a proximal end of the cartridge. During use, the cartridge, sealant, and pusher member are advanced over a positioning member and into the puncture by advancing a cartridge hub carrying the tamping device. When further distal advancement of the cartridge is limited, the cartridge hub is further advanced, activating the tamping device, and causing the pusher member to advance relative to the sealant to compress the sealant within the puncture.