Hm strange. How about creating an object to visually represent the position of the right stick and having the bullets fire and set angle towards it..
Always > Reticule: Set position
X = PlayerSprite.X + XBox360Controller.RightThumb(1)*100
Y = PlayerSprite.Y + XBox360Controller.RightThumb(1)*100
Reticule would be the new object you create and the *100 is important as the actual output from RightThumb is only a tiny decimal :)
Then just when you spawn bullets fire towards and set angle to the 'reticule' object.