And now try doing the same but without the use of unlockables :)

I applaud you my good sir

Game doesn't count taken damage in sections like that since it's unavoidable

Wow. you were saying without damage and you got damage at arms room where they come from the ground

That's how i did by myself

Thanks man. I will have to figure out how to beat it faster than 2.5 hours then. I guess its possible on easy.

The enemies on nightmare have too much health to shoot them. For the most part it'll be faster to stun them with a camera. But watch out the suiciders (who armed with glocks), because they deal about 45-50% damage per shot on middle range and instantly kill you with a headshot on close range. Of course, they can be stunned as well, but in that case you have to react very fast, because they start shooting right after spotting you. Their weakness is they can be killed by a single shot in the head as well. Let me know if you have any other questions.

Any tips how to beat diffucult playthought?

Yep

So how famas works? it has unlimited ammo?