» Find an Axe, Silenced Makarov, Amphibia, Silenced CR75 and ammo for them, .380/.22/9mm.

» Hit infected's head while they are unaware of your presence, you will then always one shot kill them.
• With the axe, you'll need to aim the aimbox a little above their head to get this done.

» Hit infected's head while they are startled or running at you, the results will be as follow:
• Wooden Axe - 3 hits.
• Firefighter Axe - 2 hits.
• Silenced Makarov - 2 hits.
• Amphibia - 3 hits.
• Silenced CR75/Glock - 1 hit.

The same results will wield when you hit their bodies, it is as if the head hit box went gone after they are aggro and everything counts as body damage.

I've tested .22 Amphibia on many infected today, killed a lot of them while they were unaware of my presence with one shot to the head by any side, but if they get on that alerted state where they shake their head searching for you before running at you, the head shot wont work, and you will need to shoot them 3 times to kill them.

.380 is the same thing but 2 rounds.

Even 5.45mm is 2 body shots to kill after they aggro.

But 9mm is 1 shot anywhere on the body.

I believe head damage should persist even if the infected are running at you, it's hard to hit them when they start running, and with a 9mm round you can one shot them in the legs if you want to, effectively killing 15 infected with a glock or CR75.

The same thing goes for melee weapons, no one shot head damage if they are startled on you. If we manage to hit the infected in the head with the axe or any proper melee weapon, they should go down, even if they are going crazy on you.

All firearms from 9mm downwards should be 2 shots to kill on body. The high caliber ones should be the ones that one shot body shots.