20x110 H-S markings query

[Tmine35]

Case headstamp is RG 53 20mm. What means the marking stencilled on case side: TH 28 54 SAPIRIZ ?

 

[TonyE]

These are the filling station details.
TH - Royal Ordnance Factory Thorpe Arch
28 - Lot number
54 - 1954
SAPIR1Z - Semi Armour Piercing Incendiary Representative Mark 1Z

Regards
TonyE

 

[Tmine35]

Thanks Tony, a bit strange subject to me.