TWO weighings can determine which one AND if it is heavy of lite. But luck would have to come into play, and only 3 of the 12 bullets would be wieghed. 1 of those bullets being the odd one. In 2 weighings we would have determined both which bullet is odd and heavy or lite. 1 weighing will be balanced and we know BOTH bullets or correct. That's my story and I'm sticking to it!

IF luck and chance is allowed then 2 weighings could do it. Here is how, luck of the draw assumed:

Pick any 2 bullets and weigh them....scales balances telling us that these two are NOT the odd ball. Now get REAL lucky and choose the odd one. The scale will tell us that it's not ballanced AND we know that the bullet left on one side IS of proper weight, the odd one will not ballance and will show wheather is it heavy or light. Now, with no luck......

Make 3 groups of 4each, being group A, B, C, each having 4 bullets.

Place 1 group on each pan A+B=1 weighing....balance? NO. So we now know that AorB groups contains the odd ball, but which one? But now we also know that the group C unweighed is a GOOD group!

Take group B off and place C on the scale, leaving A.....balance? NO So, we now know that the odd one is in group A! AND we recall that A was heavy BOTH times= 2 wieghings.

Now clear the scale and split group A in half, A1 and A2 of 2 bullets each (Remember we already know that the odd one is heavy) Weight the 2 gorups against each other. A1 indicates it is heavier that A2. 3 wieghings.

Split A1 and place 1 bulet per side, the heavy one IS the odd ball!!!! IF the scale balances then we know the 1 bullet removed from the heavy side is the odd one.4 wieghings.

NO matter how a person mixes up the bullets this method will ALWAYS find the odd ball, wheather it is heavy or lite......4 is the correct # of weighings, WITH certainty and NO luck.