... How do the numbers compare to the Vickers S 40mm ?...

Robert: Here's a few numbers together comparing the 'S' Gun with KDB. I've added in the COW Gun (OQF, 1 1/2 pdr, Mk III) for comparison - since the 'S' was effectively a short-barrelled version of the long-recoil COW Gun re-designed to take Vickers' 2-pounder 'Pom-Pom' ammunition in place of Coventry's longer rounds.

Weights, Gun Only : KDB = 1,532 lbs; COW = ~200 lbs; 'S' Gun = 320 lbs

Weights, per Round: KDB = 3.45 lbs ; COW = 1.43 lbs; 'S' Gun = 3.97 lbs

Ammunition Size mm: KDB = 35 x 228B; COW = 37 x 190R; 'S' Gun = 40 x 158R

Length, Total Gun : KDB = 15.55 ft ; COW = 7.64 ft ; 'S' Gun = 9.74 ft

Length, Gun Barrel: KDB = 10.33 ft ; COW = 6.23 ft ; 'S' Gun = 5.57 ft

Cyclic Rate of Fire: KDB = 550 rpm ; COW = 90 rpm ; 'S' Gun = 100 rpm

Magazine Capacity : KDB = 56-rd belt; COW = 5-rd clip; 'S' Gun = 15-rd drum

Muzzle velocity : KDB = 3,855 ft/s ; COW = ft/s ; 'S' Gun = 1,870 ft/s

A few anal-retentive notes:

The 200 lbs usually quoted as COW Gun weight included the mount (I haven't been able to find a 'gun only' weight for the COW Gun).

In the suffixes on ammunition, 'R' is for Rimmed, 'B' is for Banded (referring to the copper driving-band which surrounds the steel projectile).

Cyclic rof are a bit of a nonsense. Obviously, no-one ever got 90 rpm out of a COW Gun using 5-rd clips!

On ammunition capacity, the 'S' Gun began with a 12-round drum but service types had 15 rounds. There were unrealized plans to ditch the drum in favour of belt-feed.

You will see muzzle velocities for the KD series of up to 4,725 ft/s ... but that's for APDS ... and you don't really need your turboprop hoovering up discarded sabots

Muzzle velocity listed for the 'S' Gun is for AP Mk.VI (m/v for the lighter AP Mk.I rounds would be higher).