Guns are weird in this game cuz the raygun thing is more for aesthetic reasons than like something born from serious world building, because it doesn't matter to story's focus. 

The canon explanation is that the raygun mechanic came about from it being easier to make one over powder weaponry, which while existed fell aside as guns were really only used in the sky world for shooting sky varmints and the occasional monsters that would sometimes pop during dredging expidtions and occasionally on the islands. Bullet shooting guns exist but gunpowder is obsolete since the magic rock can just propel them itself. 

Anyway, if by 21st you mean guns that are like capable of semi and full firing surr. Anything else is pointless since real world principles don't apply. Go ahead and make that revolver pepperbox rifle, it'll work here.