Perhaps 20x96B should be 27x96B?
The following is a quote from the thread 27 mm Experimental http://www.bocn.co.uk/vbforum/threads/93858-27-mm-Experimental, post by “EODGUY”:
“As far as I know the 27x70Bmm rounds were developed by Olin Mathieson, East Alton, Illinois. Several variations were made (HEI (T144), Target Practice (T142), Dummy (T143) and High Pressure Test), but in relatively small quantities. One pilot lot of about 50,000 rounds of the HEI were made for testing. I do not know when the contract began, but it was supposedly sponsored by the Army Ordnance Corps and terminated in 1955. Even though the Ordnance Corps sponsored it, I have always heard it was for an airborne gun system. The projectile length for the HEI was 113mm and it weighed 250 grams with the fuze. Velocity was given as 615 m/s (2,000fps). I have never seen a photo, or a round, of the actual fuzed HEI cartridge. The electric primed cases for the rounds were made in both brass and aluminum. There was also a long cased version with a shorter projectile. This round was the same overall length as the 70mm case lengthed round. It had a 96mm long case. A velocity of 860m/s (2,700-2,800 fps) and a projectile that weighed 200 g with fuze. I have never seen an example of the long cased version.”
And from PetedeCoux’s photo, posted above, concerning Pete’s use of the descriptive term “Winchester” for the 27x70mmB cartridge:
From MIL-STD-1461E 1990 AMMUNITION MANUFACTURERS AND THEIR SYMBOLS: