The Brits developed an APDS round for the 6-pounder, available from March, 1944, that had some remarkable ballistics and kept the gun useful long after it otherwise would have been useless. Don't know if the aerial version utilized these rounds, though.
The APDS round was never used in the Tseste, presumably because the sabots might fly back and damage the airframe. There was a squeeze bore round and barrel developed for the 40 mm anti tank gun though. The barrel tapered from 40 mm down to 30 mm and a special round developed that would reduce in diameter as it passed through. The idea was pretty much the same as the sabot, a large diameter to pick up energy from the charge and a small diameter once it left the gun for better muzzle velocity and low drag. It worked pretty well but was not adapted, partly because the barrels wore out very quickly and also because cannon-firing anti-tank aircraft were by then considered by the RAF to be too vulnerable to AA fire.
In AH the Tsetse would be a nightmare for GVers, but A2A you'd do better with a Mk VI as its a fair bit lighter and if you can't take out any plane with four nose mounted Hispanos you probably won't with the 57 mm either.
