Fri Nov 13, 2015 12:59 am by Robotnik
Haven't worked with that lock specifically, but from your description, sounds like it may be the incorrect key. From similar locks I've used, the key will go a quarter turn relatively freely, then - with the correct key setting the levers and retracting the bolt - continue rotating another quarter turn to free the shackle.
Have you tried smoking/sharpie-marking the key to see if you're encountering any obstructing wards or binding levers?