Generally, I calculate this as the (Base Weapon AP X3) + 4 (APDS AP)
I don't apply the penalty because there is no spread of bullets - only 1 line.
I also tend to allow this with the Depleted Uranium bullets, as that makes sense. Not RAW, but from the description of APDS and Depleted Uranium, it is reasonable.
OTOH, the opposition can use it in the same way.