I see it’s not the case by looking what he is trying to make, even if you could make Map in Array or Array in Map (which Maps is still is not officially implemented in blueprints) i would say he is doing it wrong anyway. From description he gave he should at least create array with structure, or even class as a weapon (but you can access default properties via blueprint so it might not be easy to do it with classes)
But i also think multidimensional array, at least static dimensions number once should be implemented