pp.98SO talks about how ammo could be hit by a crit on aerospace units to some degree. It speaks of rolling 1d6 for ammo tonnage if the weapon/ ammo in question exists in arcs other then the one hit.
The question becomes how does this apply to Capital and Sub-Cap weapons? Some of those items, talking up more then one ton per shot, could conceivably negate the crit of the 1d6 rolls low enough . . .