Yes, for those you need quality steel and machine it with precision, every single one. You can not simply make a larger reactor to scale production 10x.

For artillery ammunition?

Fuck, man, artillery shells are made to fired in the thousands. Dumb rounds, at least, require no such level of precision - and, for that matter, making a ‘larger reactor’ is an oversimplification of the process necessary to scale the production of explosive material.