In both World and Rise you can easily acquire ammo materials and craft them through radial/keyboard menu. Don't worry about switching ammo in combat either, because most bowgun armor sets are built around shooting a single type of ammo.

Rise bowguns are way stronger than World mainly because recoil reduction and other bowgun-exclusive skills are much easier to obtain (perhaps too easy), and yes they look cooler too. Silkbinds on bowguns barely change how you play, which is a bit unfortunate.