Trail Arm Only Bunker Swings

Just like with the finesse wedge swing, there are a couple of advantages to doing a right arm only swing for practice in the bunker. First, because the right arm is in a relatively weak position at the top of the swing, you will be more inclined to create speed by letting the club drop as opposed to yanking the club forward with the left arm. 

Dropping the club and letting gravity help you speed up the downward movement helps to create a narrow swing arc. Second, because the right arm is further away from the target, having the effort there tends to help get the shaft more vertical (and use the bounce) as opposed to the amount of shaft lean that the left side would create. After you have a feeling of those 2 keys, add the left arm on at different places during the swing. The top of the swing and the follow-through can be great checkpoints for this. You can then see where your "normal bunker swing" (the one you are trying to improve upon) is different from your "right hand only bunker swing" and make adjustments until they feel similar.