A bullet fired from a gun makes a small hole in glass of window due to:

It happens because of the inertia of the glass molecules.

A bullet moves at a very high speed. When it hits the glass, only the small portion of glass molecules in its direct path get disturbed. The rest of the glass doesn’t have enough time to share the impact and move along. As a result, the bullet just pushes through, leaving behind a clean, small hole.

If the bullet had been slower, the force would spread across the surface, giving the surrounding molecules enough time to vibrate and break — and the whole glass might have cracked or shattered.

A bullet fired from a gun makes a small hole in the glass window because it moves with such high speed that only the particles in its immediate path are displaced. The rest of the glass stays undisturbed due to inertia, leaving just a neat hole instead of shattering the entire pane.