The windshield is considered the most delicate part, so back in the first wave of hijacking I was involved in testing 747 windshields for bullet impact from the inside.
We made a glass / plastic laminate windshield. In tests, a NATO rifle round penetrated about half way through. A 38 magnum got through the outer glass ply, and that's about it. Splat! No penetration, no structurally threatening damage from either. None.
Later 747s used an all glass laminate from another company because it was cheaper, but I doubt the results would be all that much worse.
Something designed to flip off a head-on collision with a duck at 420mph is pretty tough.