Why Medieval Era?

I thought that was because if you surrounded someone and shot, you'll be shooting your own people after the bullet goes through him? lol. 

Chip bah, use the intercourse... cough.. I mean the Force.  

For instance, although not magic, human's actually believed that anybody who could float in water was a witch or madman, as people during this time didn't actually know how to swim.

To them, floating in water is just "sorcery," similar to how one would be shocked as to how one would feel if a whale, who was found washed over up, suddenly exploded. (It actually happens)

They'd feel shocked, and run away for their lives, as to them they just saw the 'devil's wrath'. 

To half-ass it.



Since in the future magic and technology has already developed. 400 different types of magic, additional fundamental knowledge prerequisite to the magic casting . Then we'd have to do more world building, make it more complex . The reasoning of antagonists would also have to be less barbaric or simplistic . Demon Kings would have to play more Machiavellian politics , heroes playing more like marines . I simply doubt that in the future (if magic existed), we would be relying on magic like in medieval times .

As an author, that would be my take on it.
 

If it's more efficient, then that would likely happen, and they would at least try to implement it in some way. 

If it's that, then it would work, and a good way to implement it would be to use the new elements in the story. For instance, you could use magic as a driving force, but in order for the bullets to penetrate higher classed monsters, you would need to enchant your bullets with mana, enhancing the durability of the metal and also increasing the velocity speed.