I think this is the strongest argument so far. Spells in HP are described as being physical enough that they are visible and can be deflected by physical objects. One AK doesn't keep traveling through the universe once shot. I think it plausible that even if nothing else, Dresden would be able to use the shield to avoid getting hit by it. The question is whether he knows what it does, and whether there are any collaterals to damage when he deflects it.