(Nearly) got it!
Got some tech spefs for latest tungsten-core AP-T 20mm ammo for 20*102mm gun M621, while the M693 uses 20*139mm cartridge!
However, this 20*139 cartridge is also used by Rheinmetall's Rh-202, in the US M-139 and Oerlikon's KAD/HS830, which you can all find in the oobs. I guess the pen. specs should be nearly the same. Barrel length shouldn't vary wildly, and I'd the ammo is NATO standard!
So maybe this can elp. And I'll try to extract some more info from there:
http://www.giat-industries.fr/asp/us/feu.asp
Cheers, and good hunt!
Plasma