6pdr ammunition

[John McGillivray]

Here are some photos of 6 pounder rounds. The first is of the AP rounds, followed by the APDS rounds. The last photo shows the HE shell.

Was there a difference between the 6 pounder rounds used in the 6pdr Mk.II (Mk.III tank gun) and the 6 pdr Mk. IV (Mk. V tank gun)? The Mk. IV gun had a longer barrel with a muzzle break, which seems to point towards a larger propellant charge. Is this true? If so what was the details.