nato doctrine doesnt rely nearly as much on artillery since they (believe they) have the capabilities to establish air superiority. most likely, air power would replace a lot of what ukraine and russia do with artillery, at greater cost but with more precision

It honestly makes me a bit pessimistic to see that it takes us years to build a factory like this. I would like to hope that we're capable of building the tenfold of this in months if shit hits the fan...

There's a huge difference between "let's build a factory to make as much profit as possible" and "let's build a factory to stop the invasion from killing us all". Most of NATO is currently on the former, not the latter.

Factories take time because the people them want them to be highly optimized and profitable. And they're competing with toothpaste factories, TV-frame factories and factories that make ringlights for influencers. Most of those problems and requirements disappear when you're actually at war.

Honestly, at this point, war footing for Europe or America would at best cut the time in half. And that is being generous. Truthfully it may shave months off at best due to the lack of meaningful factories to convert.

On the other hand, we have a lot more diverse arms beyond artillery shells that would both need production increases as well as stockpiles we would empty in the meantime. Aerial bombs, other ground based missile platforms, possibly even other artillery shells that are simply not compatible with Ukrainian systems currently in use.

America in particular is not a heavy user of artillery for the prior 50 years, and mostly as defensive weapons currently. And the American military would be pushing to turn it from a defensive to offensive war as soon as possible.

Russia produces 2million 152mm and 122mm shells per year. Rheinmetall alone is at 700.000 155mm shells per year by 2025 alone. The difference is not that big, but many European countries are increasing stockpiles and there is a need to train their own militaries, which requires firing some of them.

However the number of shells matters much less then the enemies they destroy. NATO artillery is much much more precise. So they need one shell to hit a target, whereas Russia might need ten. The other big part is air power. NATO unlike Ukraine can destroy Russia air defence and then use a lot of bombs to create a break through in the line. This just can not be easiyl transfered to Ukraine, as training pilots and ground crews takes years.

Russia is on a war economy while Europe and the US is not. I guess that explains the difference a bit and also would change quickly if Russia attacks NATO directly.

Ukraine wins when it has 1:3 ratio of artillery shells to Russia. Which means Russia needs more than three times more shells to make progress on the front. It would seem they're getting better now with jamming and drones, but I think they currently are around this ratio, and Russia is not doing much progress.

Nato has more and much more advanced stuff than Ukraine. So I don't know if 1:6 would be enough, but Europe has a lot of margin to increase its production and don't need so much more than that to stop Russia.