func spawnBullet() {
let bullet = SKShapeNode(circleOfRadius:30)

//set other properties here...

self.addChild(bullet)

}

var bulletNode: SKShapeNode?

func setBulletProperty() {

let bullet:SKShapeNode? = SKShapeNode(circleOfRadius: 30)

//set other properties here...

bulletNode = bullet

}

func spawnBullet() {
let newBullet = bulletNode.copy() as! SKShapeNode
self.addChild(newBullet)
}