How realistic was Emily Blunt’s character’s reaction to being shot while wearing body armor at about 8:53 in this video? Sorry, I couldn’t find a shorter clip containing this scene.
I don’t know that there is a single “right” reaction to being shot. It depends heavily on the thickness of the armor, the caliber, and the muzzle velocity of the projectile.
Just an FYI, you can add the start time on a YouTube link… ?t=8m53s
Have we done yet, the Second Chance guy shooting people with .308 while wearing his company’s vests? (I’m wondering just what besides kevlar is in that vest.) IIRC, in the 70s and early 80s, Richard Davis, the CEO of what was Second Chance body armor, while trying to sell police departments on the idea of body armor, used to shoot himself with the policeman’s own service weapon. No broken ribs. And it doesn’t look like the shootee in the video above suffered any kind of injury like that. OTOH, I have read accounts of LEOs getting shot in their vest, and suffering bruising/broken ribs. YMMV depending on your vest and just how you get shot, I guess.
Anyway, as sasquatch wrote in post #2 of this thread, provided you’re expecting the blow, pretty much all small arms bullets aren’t going to knock you over from just the momentum of the bullet. What knocks you over is your reaction to getting shot or if you’re otherwise off balance.
The rifle bullet might go through a vest … While it might reduce the velocity the trade off is that the vest may have helped reshape the bullet , flaring it out to do MORE injury even when lesser speed. The vest might help reduce injury from a snipers steel jacket bullet, as it will reduce speed but not deform.
(the sniper needs to go through glass and similar and still have the bullet travel straight. Depends on his choice of bullet at the time… He might know he has no glass in the way… )
In 1984? It’s most likely steel trauma plate inserts.
As an aside, I remember in one of the Police Story movies, Jackie Chan is trying to talk down a hostage taker with a gun, and the confrontation ends with the hostage taker taking a shot at Jackie before being subdued.
Naturally, Jackie rips open his jacket to reveal a bullet proof vest! Followed by one of the other cops saying that it was a good thing Jackie was wearing two vests because that shot would have killed him at that range otherwise. Cue Jackie removing the vest to reveal another vest layered under it.
On the contrary, I’d complain a LOT more because I’d be alive to complain. You wouldn’t hear a peep out of me if I were dead. 
That doesn’t look like soft body armor police officers typically wear under their uniform.
I went on the job in '82. I had a hard vest that was steel plates though not multi layered like that. It was worn over the uniform and was more tactical. My first soft vest was about circa 1984. I’m pretty sure the trauma plates were a type of ceramic though they were also covered in Kevlar so I couldn’t be sure. They went in a little pocket in front of the vest in front of the Kevlar panels just like they are today. You wouldn’t believe how much heavier that vest was (level 2) than todays level 3’s. Todays trauma plates tend to be soft as there is a theory about bullets following a hard plate upward into an officers neck/jaw. Don’t know if that’s ever really happened.
About 1 1/2 years ago I was at a demonstration where a level 3 with soft trauma plates was fired at with .223 from an AR15. Went right through it. The vest was of no help whatsoever.
3A.
I only nitpick because the difference between NIJ Level 3A and 3 is huge. It’s the jump from soft armor to hard armor; from handguns to, well, those .223 rounds among others. Level III would have stopped them quite easily. IIIA doesn’t stand a chance.
Yep, you’re right, it was a 3A. Typo.
Of course, “stopping a bullet” isn’t a binary yes-no. It’s also possible for a vest to let a bullet through, but still slow it enough that it turns a mortal wound into a survivable one.