Why we always gotta start with muskets every time they put guns in these fantasy worlds.... Could have could have went straight to a repeater or revolver even break action pistols and riffles would have been good..🤦🏿♀️
Maybe it's my own lack of knowledge of firearms, but I get the impression that muskets and cannons are easier to manufacture than all of those things you mentioned. Especially for some random person that got reincarnated.
Cannon/musket: Make metal tube that has one tiny hole for a fuse, and one big hole for everything else. Scale up appropriately for cannon / down for musket. And it doesn't matter if the tube is too thick, just makes it heavier.
For actual firing: Shove powder down this tube. Shove metal ball down this tube. Shove wadding down the tube. Light fuse.
Versus building very consistent bullets with thin metal caps that don't explode in the barrel, complicated revolving mechanisms, precision rifling down the barrel, repeaters that don't jam...