He didn't serve in a Royal Horse Artillery regiment as the OP writes. He served with the Royal Field Artillery and was with 242 Brigade when he died in action in March 1918.
MaxD
PS for the record, the Royal Horse Artillery (RHA) and the Royal Field Artillery (RFA) were both administered by a single record office that is written as "Royal Horse Artillery and Royal Field Artillery" or RH and RFA which often confuses.