I was recently thinking about which technologies an Isekai-Protagonist could give his allies in a medival fantasy world. For all those who don't know, Isekai is an anime genre where the protagonist is a real world human who get transported into a fantasy world. Come to think of it, this question applies to time travelers as well.
Assume that I've joined a local lord after I established my value and that I'm a respected advisor. Since he is at war with the good guy empire, I decided to help the war effort by introducing gun powder to this world. I don't know the exact formula, but I know that I need charcoal, sulfur and salpeter. With the might of the scientific method and the more or less voluntary help of laboratory slaves I'll figure it out.
However I'm uncertain which application of gunpowder I should pitch to the Dark Khan. Sure, splinter granades are a no-brainer, but I feel that I can do better. While I'm certain that I could teach the artisans the Overlord bound in this service conquering far away lands how to make guns and cadnnons eventually, I want to show results quickly.
The basic idea is to build large splinter bombs to devastate the enemy heavy infantry. Horse archers, shock cavalry and auxiliaries will do the rest. I want to use catapults to launch the bombs. Figuring out artillery maths was one of my early projects, so accuracy shouldn't be an issue.
I got three projectile designs in mind. All are strong, waterproof sacks filled with an outer layer of gunpowder and shrapnel, an inner gunpowder core and a lute. The first design is as simple as that and could be made quickly. However I'm wondering if having the bomb explode above ground would be deal more damage. This would mean that I would have to work out the timing of the lute. Another, even more complex idea of mine was to attach a wodden pole with large fletchings. I hope that this would make it predictable which side would be down during the fall. This might allow me to improve the bombs inner structure to some sort of directional bomb. This would of cause require even more research to figure out. Which of these designs is best? Does the improvement of the bombs performance type 2 and 3 would bring really justify the extra effort? Or are my bomb catapults a bad idea all together and I should use the gun power in another way altogether to help the war effort?
Note that sieges aren't the issue, large field battles are. Our shamans got biological warfare down to the pont that most cities prefer to surrender.