var bullet = preload("res://bullet.tscn")
first You you change the path to resource ( like take a blueprint of a scene)
var bulletinst = bullet.instance()
next You create individual object using this blieprint.
bulletinst.global_postition = gun.global_position
finally You set any variable to this individual object
Generally You always have to call a blueprint once, and than instance() this blueprint as many times as many bullets You want