The trick to bunker shots is to get the correct set up, you need a wide stance because it is a big swing, open stance, weight and ball even or slightly forward and go through with your body not your hands
A common mistake on the backswing is to hinge instead of cock your wrists, a perfect drill to help fix this is to pre set your backswing by cocking your wrists right up in front of your face at address and then turning into a full backswing
Changing your grip is uncomfortable so the best place to work on it is at home, holding the club a few minutes at a time until it feels comfortable enough to swing with