That shot was a glancing blow and would have gone through had it been a direct hit. The stupid part (done for the movie effect) was him taking it off and looking at it, as he clearly was in sight of someone shooting, maybe a sniper, and he should have taken the lucky bounce as a warning he was an easy target. But also, that beach was a slaughterhouse so the odds were still not great to survive even if he had taken cover.

Surviving a headshot isn’t particularly likely in any scenario. Helmets are more to stop shrapnel, glancing blows, and- depending on the helmet- maybe pistol rounds. Realistically, a helmet just isn’t stopping a direct shot with a rifle round.

Saving private Ryan is a movie

Better bullets.

The armor soldiers wear is only gonna stop so much. Smaller/slower bullets, especially hollow points. Bigger, faster, solid core/jacketed rounds are meant to penetrate armor, and you’re only going to have so much protection vs how much weight you can carry.

No idea but I’d guess armour piercing rounds being commonplace these days?