I picked up this helmet a couple of weeks ago and have just got around to looking at it closely.
It is marked HS for Hadfields Steel but has no heat/ batch number.
From what I read here Brodie helmets, Heat numbers/Batch numbers - Other Equipment - Great War Forum it could be made between November 1915 and September 1916 as it does not show the Heat number.
Does this sound about right ?
Colouring shows Olive Green under a sand colour paint.