When you start parsing out the biography of James Milton Campbell, Jr., known to the world as Little Milton, his story starts reading like he was some Forrest Gump of the blues, a guy bouncing around the timeline of music in the ’50s, ’60s, and ’70s, part of seminal history, but never at its direct center. Through him, you get to Sun Records and Elvis Presley, and Stax and Otis Redding. Through him you get to Albert King and Fontella Bass. Through him you get to Etta James, Chess Records, and the legendary Wattstax concert film. Despite lodging only one No. 1 R&B hit, playing Six Degrees of Little Milton ends up a survey of American music in the mid-20th century.