Determine the direction of force.

When the evidence includes the breakage of glass by a bullet,  the direction of bullet travel can easily be determined.  Find the sharply tapered glass pieces nearest to the hole (radial break pieces).  Be sure you know which flat surface is the inside (or outside!) and look at the glass piece from the side. 

The force of the bullet hitting one side will break away a crater on the opposite side!  The glass is tapered... from the impact surface away to a larger hole on the opposite side from the impact.  This “rule” is also true for surfaces such as “particle” board and gypsum board used in construction as well as in human skulls!

Be careful with larger holes such as those left by large rocks... The “rule” is still true, but the pieces remaining around the larger hole may not always be the right ones to evaluate for “directionality”.

Fracture lines radiate from the break.  Find a piece near the break  and examine the area where the lines come closest together. Turn it to look at the edge as in the view to right.

 Which way was the bullet traveling?

Which surface is still flat and which is cratered?  What direction was the force? (Remember - Flat side faces the shooter! Crater Away from the shooter.)

You are correct if you said the bullet was traveling (as depicted in the above photo) from the top to the  bottom of the view.