GREENEVILLE — A 43-year-old Kingsport man has been sentenced to 10 years in federal prison for his role in a two-year-long “gravel” distribution ring in Sullivan County. Michael Ray Mangum received the 120-month prison sentence last week in U.S. District Court in Greeneville. Mangum was one of 10 people indicted in August 2014 on a 35-count indictment charging them with numerous drug, conspiracy and weapon charges and maintaining a dwelling where drugs are manufactured or distributed.