A real life example can be found in the movie Tora Tora Tora.
Adm Kimmel, is watching the attack on the fleet at Pearl Harbor from his HQ, standing behind a set of french doors. A bullet breaks the glass, and strikes him, bouncing off his uniform jacket. It was reported as having been a "spent" Japanese 7,7mm round.
History is full of examples of bullets being stopped by various things, particualy things not usually thought of as "bulletproof".
Most of the time, there's no way of knowing what speed those bullets were moving when they got stopped. Often in combat, they're not doing full muzzle velocity.
when the stars line up in just the right way, the most unlikely things can happen.