I'm hoping someone can ID the cannon case shown below. Its dimensions are (to the nearest mm):
Diameter at case mouth: 65mm
Diameter above rim: 68mm
Diameter of rim: 76mm
Case length: 249mm
12 o'clock: KN in cylinder
2 o'clock: IV
3 o'clock: C
6 o'clock: 3 ^ 93 (^ is a British broad arrow)
8 o'clock: S followed by a spear-like symbol
9 o'clock: F
All markings except the ones at 2 o'clock and 8 o'clock are struck through with horizontal lines, so presumably this has been reloaded at some point.
Additionally, there are two rectangular notches cut through the case about 12mm below the mouth, spaced 180 degrees apart. Here is a side photo of the round next to a 30mm GAU-8 for scale, as well as a photo of the headstamp (sorry for the poor-quality images!).
Am I correct in assuming that KN indicate King's Norton Metal Company?