To add to this here is another clip on the same server (ZERO Deer Isle) of unconscious from a double blaze shot to the head. At the time I thought Infected knocked me out but maybe it was the double blaze shot. This unconscious length makes perfect sense to me given the caliber and that it was a head shot. https://www.twitch.tv/videos/1095598117

i think uncon timer also depends on targets wearing armor, helmet, also on hit body part. Its definately not only bullet caliber and specific gun.

Yes, armor can have a shock multiplier, you go unconscious when your shock health goes below 25 and regain consciousness when it reaches 50.
Bullets have a shock health regen modifier, 308 has 5x modifier, so if you are hit by a .308 round and your shock goes below 25, you go unconscious and wake up 5x faster compare to being knocked out by melee.
Also consider that sometimes the shock health only goes to 24, sometimes to 0(0 is the floor), depending on armor and previous shock health and bullet, which will also affect unconscious times (having to regain 24 shock vs having to regain 50 shock).

Melee damage and zombie damage has 1x multiplier, you can learn more about the multipliers by searching the game .cpp files for unconRefillModifier,which is applied in scripts\4_World\Entities\ManBase\PlayerBase.c Line 728 in the EEHitBy function.

This feature is undocumented and confusing to users who don't unpack the game files and it's not explained in-game at all.

This is little bit related to why double blaze headshot wasn't a kill.

https://feedback.bistudio.com/T160188