When playing out of hard packed bunkers be sure to lean your shoulders toward the target. By this I mean playing most of your weight on your front foot, and a slightly open stance. Open up your face and play the ball about 12 inches behind your foward foot. If you lean toward your target it forces your club into the sand first, preventing the bounce of the club from skidding into the ball which results in a "skulled" shot across the green. You may also find it easier to use a higher lofted club than the sand wedge, i personally prefer my lob wedge from tight bunker lies. When you get used to playing out of firmer bunkers, you will find that it is actually easier to spin in out of these type bunkers.