Hello, I have a round of what I believe to be 20mm Oerlikon. It has SWN/68/56/HF IT/TNT/13Z
I’ve found out the SWN means it was produced in Royal Ordnance Factory Swynnerton, I’m guessing 56 was the year of production, and it’s obvious what TNT is, but I’m curious about the “HF IT” marking and the “13Z” marking. I would have expected something like HE IT (High Explosive Incendiary Tracer) but I’m sure it’s an F as the shell is well preserved.
I’m also curious about what appears to be paper residue stuck to the side of the shell.
Does anyone know what the HF IT and 13Z might indicate and what the paper-like material might be? Thanks.