And this is precisely why there is a temporary shortage of ammunition. The makers of ammunition won't increase production because opening new factories for a temporary increase in demand doesn't make any sense.
What about adding an extra shift to get through? Like running 3 shifts instead of 2. That's what they do in the automotive industry when the demand is higher than they expected and the orders are backing up....
Then when they "catch up", go back to one or two shifts....
They don't have to build another factory to do that...