Undead Sharpshooter

Rank 1 - kill 5 undead in 10 seconds using a gun.

Very simple and you will do this automatically when you progress through the story. If you find this hard then change your targeting setting to casual.

Rank 2 - Headshot 10 undead in a row 

Use the casual targeting setting and you will aim automatically to the head. Kill 10 zombies and you will progress to the next rank.

'''Rank 3 - Kill 5 flaming undead in one dead eye meter. '''

There are two ways in doing this. One is to save theives landing and use the firebottle and light a group of zombies and finish them off in dead eye. This is the harder method. The second method is to use phosphorous coating on your bullets and go into dead eye and kill 5 zombies. This method works and you will progress to the next rank.

Rank 4 - Kill one of each undead types in one dead eye meter 

For this go to el presidio and outside the gate a group of zombies will spawn. There will be the 4 types of zombies required for this rank. Go into dead eye and paint their heads and let it rip. You will be promoted to the next rank

Rank 5 - Kill 5 undead sniper kills in 8 seconds ( without dead eye) 

For this first of all you need a sniper rifle. You can save plainview to get the rolling block rifle. Then go to jorge's gap which is near coot's chapel. Go there as the zombies are crowded together. Aim and try to get a multi kill in the first shot. If you dont its okay just aim for the heads and shoot them. The execution move also works so you can go near and use the execution move with the rifle to kill 5 zombies.