Please correct me if I'm wrong, but I believe you need to shoot through 200 hp if you account for 2 armor plates. In addition to that, weapon balance seems to be slightly tweaked, so you may need more bullets to kill.
This means that it's not uncommon for a gun, even at close range to require 8-10 bullets if they are not headshots. At a distance the damage drop off kicks in and it could require about double that amount.
Damage drop off tends to affect BTK/TTK after roughly 20 meters for many of the guns in the game.
Add hit detection issues due to 80% of a BR game running at 30 hz, to the equation and it could require far more. If they'd just make it 60 hz, it'd probably feel like the TTK was sped up.