I'm looking for something like Release that Witch where the protagonist brings in modern assets in a fantasy/medieval settings. No, It should be that the mc makes them using what he has and not be reincarnated with a bunch of tech at the start.
Tales of the Reincarnated Lord is a favorite of mine and has what you're describing but the start is abysmally slow because it starts more as a slice-of-life novel about the MC and doesn't switch to Kingdom building until later. Also, it takes him a long time to make guns and he instead invents catapults. And he never manages to make glass or concrete. Common Sense of a Duke's daughter has a lot of technology introduction but it is a shoujo and didn't have any large battles in the parts I read. The Defeated Dragon might get there eventually but it is also slow paced and the MC is not particularly likeable.
Totally forgot to recommend Isekai Tensei Soudouki. It doesn't have exactly what you are talking about yet but I believe that it will get there.
A Hero's War, more like technology uplift rather than kingdom building with MCs as central figures of development Akuyaku Reijo Ni Koi Wo Shite Rakuin no Monshou, gun and sword story setting, they use guns but because human depleted their resources and record it make gun less sophsticated than our counterpart. Mother of Learning, guns are still in early development but they sure can kill mages and monsters Illustration from Maquia: The Promised Flower Blooms