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”.