[Rules] Bombardment Chart - Example

[ACav]

Split columns are irrelevant here because they both resulted in "X". In this specific instance, all we have is a singular Bombardment attack that resulted in an "X" as the CRT result. Accordingly you resolve it as an X, resulting in 1 step loss to 1 combat unit (owner's choice) + removal of one transport.

Forcing the prioritization of the AT gun because of its +1 modifier apparently is a house rule that others use, but its not in the actual rules. A combat unit is a combat unit is a combat unit. This was a specific change going from second to third editions, and then carried into fourth. 2nd Edition has special rules for losses to weapon units but lets not dig into that to confuse people even more. 

When it gets complicated is when the columns find a different result. Say the roll was an 11, still on the 21 and 30 columns. In this case only the AT gun would "see" the "X" result so it would be required to take the step loss. The INF "see's" the result as an "M2" and roll accordingly. The INF does not suffer an additional M2 as a result of the X for the AT gun as this, once again, is just ONE bombardment attack.

How does 7.5 apply here? It clearly says to apply the die roll to the different columns:
 7.52 Separate Column Modifers in One Attack - In some cases, a column modifier will apply to some units in a target hex but not others. In such a case, make one dice roll for the attack, but use different columns to determine the combat results on the different target units.

I would play it where the Art and Inf each take a step loss and the infantry then must pass a M2 moral check (per 7.6)

That would be conducting multiple attacks though, which is why the rules header in 7.52 specifies that it is still one attack. The interaction, albeit not this specific interaction is included in the example in the rules text. For those that dont have it up, a single split column attack results in an M1 to an Infantry unit and an X to a weapon unit per die roll.

If it was played as you are suggesting, with it being treated as two attacks with cumulative effects then the Infantry would receive an M1 and the weapon would receive an X, then the INF would receive an M2 from the cumulative effect of the X.

But that's not what happens, as the example illustrates. It is ONE attack you are just finding the result on separate columns, hence the weapon receives X and is eliminated, and the INF receives and M2 via the weapon X. The M1 is dropped, again ONE attack, not cumulative. 

When ONE attack achieves an X, one step is lost, not one per unit...

Sorry, I don't understand how this amount to Two attacks. It's one target hex, in one action segment, with two units with the misfortune of being on the receiving end of the combat result.

Two separate, cumulative results = two attacks

Hmm, this is too complicated and there are too many conflicting opinions about ONE bombardment action that stimulated two affects on two SEPARATE units in the same instant.

Maybe it's time to consider the great American pastime?

A single home run hit can score up to 4 runs if the bases are loaded when that lucky batter hits that baseball. That is not considered 4 separate attacks, just like this discussion is not about 2 separate attacks. The guy hitting that homer, represents just ONE action that affects what is going on ALL 4 bases of that diamond, in that moment. Both units get the results of the hit, it just affected them differently, e.g., like running from 1st base to home plate is different for the runner on 3rd base running home.