Artillery Guns and Howitzers with direct fire

[Mobhack]

That is the way it's already done for arty with a solid AT shot. (IIRC it is more common in WW2, MBT uses HEAT in the main). See weapon 117 in the UK OOB for example.

The method gets a note in passing in the Mobhack help. See the yellow box in the weapons tab, containing the following:

PLEASE NOTE:

"AP ammo" can also represent earlier or alternate versions of SABOT ammo in much the same way that "Sabot" ammo can sometimes represent AP ammo when used by on map artillery.

(Italics mine)

cheers
Andy