Guns don't really do a lot of damage and are mainly used for parries.
However, you sorta could make gun build work if you level your bloodtinge stat up. Evelyn is great high damage gun that has bloodtinge scaling and there's also a double barrel gun (I forget the name) that does high damage but uses 2 bullets per shot.
There is a strength scaling cannon but I think they nerfed it very early on so it's hard to make a build around that. There is also a
in the dlc which is quite Good and I'm sure you can make build centered around it. You could even suicide run to the weapon as soon as you unlock the dlc.
As bullets are a finite resource, you'll want to make use of blood bullets (press up on the dpad to sacrifice some hp for 5 blood bullets) and equip runes that increase your max bullets when you unlock them.
Even with this though, you'll want to supplement this with a good weapon that will also scale with bloodtinge.
