Looking down at your relatively small chest, you get an idea.
"Time to test #6," you say.
Placing the barrel of the gun against your nipple, you feel the wonderful sensation of the cold metal on your sensitive skin. Experimentally, you squeeze the trigger. All of a sudden, your hand is pushed backwards from your breast expanding. Now, your right breast is a lot smaller than your giant left breast. Putting the gun against your right breast, you pull the trigger and the two large breasts are even-sized.
"What about more?" you say, and put the barrel of the gun below your right breast. You squeeze the trigger and loose your balance because of the new weight on your right side. Getting up, you quickly adjust to the new sensation of the third breast. Pointing the gun right next to the other one, you pull the trigger and the weight evens out. You look in the mirror at your four-breasted self and smile.