another kind of Box Drill
444 is correct in his description of the "other" kind of box drill, often used as a warm up drill by competitive shooters. These should be viewed as a drill to increase the ability to engage multiple targets and change point of aim quickly and NOT as being tactically correct.
These are the variations I'm familiar with:
Facing two targets at 7 or 10 yards. Target A is on the left and Target B is on the right.
BOX DRILL: 2 shots to the body of A, 2 shots to the body of B, 1 shot to the head of B, one shot to the head of A.
X DRILL: 1 shot to the head of A, 2 shots to the body of B, 1 shot to the head of B, 2 shots to the body of A.
Z DRILL: 1 shot to the head of A, 1 shot to the head of B, 2 shots to the body of A, 2 shots to the body of B.
These are skill building drills. For variety, sometimes start on the left hand target and sometimes start on the right hand target. Vary the routine to get the most training value out of it.