The challenge in running any business is to be consistently profitable. There are times when the market is good and you make money, and times when the market is bad when you lose money. You have to make enough money when times are good so you can survive when the market is bad. As much as companies try to smooth that out with long term contracts, inventory management, and strategic planning; there are always big up's and downs. So many just settle on having a high demand product with a long order file.
Take McMillan for example. For around 20 years or so they have had 4-6 month order file. They refused to add capacity, most likely because they had been burned in a down market before. If you add capacity, when the market goes down you may well go out of business. At the best you have to lay people off and hope you have enough cash to survive the downturn.
As a consequence of McMillan not adding capacity, several other quality stock makers have entered the market. Retailers started buying ahead, and McMillan started making to inventory a little. We have seen the same thing with barrel makers.
This is going to be tougher with ammo, powder, and primers. I'll bet it would cost $1.0 Billion to build a new ammo factory today. There is great risk with that. None of the people who have created enough wealth to afford to build a new plant are likely to do that just to help out a few reloaders and shooters. I doubt if even the Trump family would take such a risk.