User blog comment:Lord Loss/Monster Hunter Frontier G Discussion/@comment-76.114.237.96-20121119031855/@comment-969093-20121219235836

SR999 is the rank that is dedicated to a weapon type. It comes with +50 base raw bonus attack power, grants access to HC/Supremacy (just needs SR) and usage of the SR moves (just needs SR) as well as the Affinity % Up bonus boost.