LoL, it doesn't work that, You don't lock in and kill one bomb at one time. It's more like thousands of bullets attacking that whole group of bombs.
You are shooting at a bomb not a missile. There is no fuel tank you can rupture or any other volatile. If 2000 lbs bomb's timer can withstand a shock of 20 meters penetration of steel reinforce concrete before exploding, those bullets will have a hard time exploding those bombs.
Secondly, you are assuming that the B-2 will fire all its weapons at one go.
Thirdly, a shock of a 2000 lbs bomb explosion, along with the shrapnel will destroy your CIWS even at 3,000 meters.