On one hand, we all love Belebro.
On the other, Roswita dearly needs high quality powder to feed her Repeater rifles, and she is unlikely to get a better deal than a Stirlandian source, while Belegar can always set up his own thing.
And, tbh, the Army of Stirland sounds hungrier for gunpowder than K8P. Also, it looks more directly "assisting the empire", too. So I think we should go for producing in Stirland.
Boney, is there a remarkable quality difference between producing in Stirland and in K8P? Or would we get Gotri's Gotriness involved?