Shooting a projectile in spritekit

Question

I am looking to shoot a SKSpritenode (a cannonball) from a another Sprite node (enemy ship). The cannonball should travel directly down toward bottom of screen from the enemy ship node. I can't seem to get positioning right, cannonball seems to shoot from the corner of the screen and not move far, the enemy-ship node is randomly chosen from an array of all halos on screen at once and the cannonball position assigned to the front of halo:

// the cannonball

ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:6];
    ball.physicsBody.velocity = CGVectorMake(SHOT_SPEED, SHOT_SPEED);

    // we dont want ball to lose speed or momentum when it hots edges so..
    ball.physicsBody.restitution=1.0;  // max bounceness of node
    ball.physicsBody.linearDamping =0.0; // dont reduce linear velocity ove time
    ball.physicsBody.friction=0.0;

    ball.physicsBody.categoryBitMask = kCCBallCategory;
    // ball.physicsBody.contactTestBitMask = kCCEdgeCategory;
    ball.physicsBody.collisionBitMask= kCCEdgeCategory;
    ball.physicsBody.contactTestBitMask = kCCEdgeCategory | KCCShieldUPCategory | kCCMultiUpCategory ; // | KCCShieldUPCategory notify

// the array of enemy ship nodes

NSMutableArray *allHalos = [NSMutableArray array];
[_mainLayer enumerateChildNodesWithName:@"halos" usingBlock:^(SKNode *node, BOOL *stop) {
    [allHalos addObject:node];
}];




if ([allHalos count]>0) {
        NSUInteger allHalosInteger = arc4random_uniform([allHalos count]);
        SKSpriteNode *shooterHalo=[allHalos objectAtIndex:allHalosInteger];
        ball.position = CGPointMake(shooterHalo.position.x, shooterHalo.position.y - shooterHalo.frame.size.height/2 + ball.frame.size.height / 2);

        CGPoint bulletDestination = CGPointMake(shooterHalo.position.x, - ball.frame.size.height / 2);

        [self fireBullet:ball toDestination:bulletDestination withDuration:2.0 ];



    }

-(void)fireBullet:(SKNode*)ball toDestination:(CGPoint)destination withDuration:(NSTimeInterval)duration  {
    //1
    SKAction* bulletAction = [SKAction sequence:@[[SKAction moveTo:destination duration:duration],
                                                  [SKAction waitForDuration:3.0/60.0],
                                                  [SKAction removeFromParent]]];


    [ball runAction:[SKAction group:@[bulletAction, _soundLaser]]];

    [self addChild:ball];
}

Any input appreciated.