Hello Flash,
the shoulder title is S Of G school of gunnery he was posted there when it was experimental establishment, the cap badge is the Royal Artillery he was with the RGA section of the R, Another thing that gets missed however there's the wounded stripe, I have all of his brass inc his Gun Layer trade and Gunnery instructors badge, The Artillery Corporals were called Bombardier.... I have looked into his service and found lost of paperwork its only been this year that I found out about the Shoeburyness Essex experimental Establishment, sadly there's no records of this and by chance I was going over some old letters and the address caught my eye "S Of G" now this is dated 1920, his regt number and Shoeburyness... it all added to the jigsaw.