Technically small calibers with low velocities, small bullet masses, and high angles of incidence would be deflected by a helmet's surface, but those aren't regarded as self-defense loads. I seriously doubt a fiberglass shell and foam inner would do well against a .45, 9mm or even a .38 or .380 round coming at it, even with as much as 30 degrees of incidence. Anyway, the main perp conveniently took his helmet off...