After all, he brings a Basilisk's gun with him for 25% of the points.
There is no extra rule that could make him shoot at another target. Members of artillery units can do so (page 55 Rulebook). But the Master of Ordnance is part of the command squad, which is classified as an infantry unit (page 90 codex). His attack is supposed to be treated as a normal shot (page 31 codex).
On the plus side, this means that he is affected from orders like "bring it down" as usual.
I would be surprised if anyone is able to show you a rule which sais he cannot receive orders. The codex sais it is supposed to be treated like a normal shooting attack. He is an infantry unit model, so he benefits from all orders as usual (not "First Rank, second Rank" of course, because he has no laser rifle).
I've read about this discussion in several forums. The strongest argument of the people who say he can't is: "Well, he shouldn't, it doesn't feel right." If you play rules as written, he can use "bring it down". Just because the chances to hit the model are not good (because he has to roll 6 or less for the scatterroll), it doesn't mean it is not allowed. Everything else is just house-rules.
I have been reading the Codex and BRB and I cannot say I don't agrre w/ you. The best roll I have hit on w/ him was a 1-1-2 w/ LOS and so hit dead on (oh on top of that I rolled a Hit on the scatter roll) that was a once in a long time hit. Actually, my to my gaming clubs ire, in tourney games I am known for the uncanny scatter rolls that don’t scatter by rolling double 1's or a combination that are 3's or at most a 4's. Lol. But that is the Dice Gods bein g kind and I wouldn't bet a win on it.
_________________ In the event that you may not know if your target is down - Double Tap Em!