Tin and lead clusters are produced by laser vaporization in a pulsed nozzle source and studied with laser photoionization mass spectroscopy. Magic numbers are observed in both cluster size distributions under a variety of laser wavelength and power conditions which can be understood in terms of ionization thresholds, relative ionization cross sections, and multiphoton-induced fragmentation. After investigation of the photoionization dynamics, relative abundances of different sized clusters are estimated. Abundance patterns of tin and lead clusters are compared to those reported previously for other group IV elements C, Si, Ge to investigate the role of periodicity in cluster growth and bonding properties. Especially abundant 10-atom cluster species are observed for both tin and lead, as has been observed previously for both silicon and germanium. Other features not observed for silicon and germanium, such as abundance patterns characteristic of atom close packing geometries, are observed to a limited degree for tin clusters and are more prominent in lead clusters.