It's actually a big mess. Nitrocellulose at lower nitrations than munitions-grade nitrocellulose is sold by Dow (though I don't know where they make it) and is used in everything from wood finishes and nail polish to ping pong balls and printing ink binders. Hex-nitrated munitions-grade nitrocellulose is made in just one facility in the U.S., and that is the U.S. Army's Radford plant. It makes both the nitric and sulfuric acids required, as well as the finished nitrocellulose hexanitrate. While making basic nitrocellulose is a simple YouTube-type process, the commercial process requires the production of stable nitrocellulose with consistent nitration, which is not quite so simple.
This paper will give you some idea of what is involved. Then you have the acid production and concentration, and that is another whole complex process. Such plants are expensive to build, and it is hard to get environmental permits to build them.
Radford produces at 100% capacity all the time, as it has for decades, stockpiling when the marketplace didn't want all their production and drawing down the stock during a surge, like a period of rebuilding military ammunition stockpiles. Additionally,
they updated and commissioned new nitrocellulose manufacturing in 2021. So, where has that fallen down? It started with the unprecedented growth in the number of US gun owners and shooters during the pandemic and the "defund the police" movement. The US civilian ammunition market is over ten times larger than the government market when the military isn't stockpiling or sending artillery shells to Ukraine. Civilians went from around 15 billion rounds annually to over 20 billion over the last four years. It is producing ammunition for that additional civilian demand that has drawn down the Radford nitrocellulose stock, and the new facility was planned before the new demand appeared, and it looks like Radford can't catch up.
Meanwhile, Europe is also trying to supply ammunition to Ukraine and has its own nitrocellulose shortage. It turns out the Europeans allowed themselves to become dependent on China to supply the grade of cotton used in their processes, and of course, China stopped shipping it a few months ago (though alternatives have now been identified). You can
read about it here. They also have problems with their own environmental permitting process, which is getting in the way of constructing new plant capacity.
It's going to be interesting to see how these things play out, but it looks like we are in for shortages lasting some additional years before production can catch up.