An ordinary bullet has gotten a little mass of just some 100 to 150 grams that are very small figures. Then what makes this little bullet so damaging and destructive?

A bullet when fired from some pistol or rifle achieves a highest velocity (in simple words you can say speed) and that high velocity increases the overall momentum of the system.

(Momentum = mass * velocity)

It means you can enhance the destructive property of some moving body either by increasing its mass or velocity.

A heavy truck at rest is not able to destruct a building as its velocity is zero. And due to this the momentum is also zero.But a moving truck will distort a building.

http://pixabay.com/en/bullet-cartridge-ammunition-crime-408636/