When evidence includes the breakage of glass by a bullet, the direction of travel may be easily determined. Find the sharply tapered pieces nearest to the hole (radial break pieces). Be sure you
know which is the inside (or outside!) and look at the glass from the side.
The force of the bullet hitting one side will break away a crater on the opposite side of the glass. The glass is tapered, from the impact surface away to a larger hope on the side opposite the
impact. This “rule” is also true for surfaces such as “particle board”, gypsum drywall, plywoods... and large bone structures such as skulls, jaws and hips.
Be careful with larger holes as left by rocks. The rule is still true, however the pieces remaining around the hole may not always be the right ones to evaluate for “directionality”.