According to Official Guinness Records,
The most golf balls hit over 300 yards in one hour is 459 and was achieved by Lynn Ray (USA) at the Riverwalk Golf Club in San Diego, California, USA, on 5 March 2016.This record was attempted to raise money for the Santana High School Boys and Girls golf team.
For a complete list of 2016 records, please visit 2016 Guinness Records in United States.