Narco Terror

This Achievement is actually rather easy since natural progression through the game have you use ALL Special Weapons so as long as you make sure to change Normal Weapons when you get them & make sure to use them,special weapons & all 4 different Ammo Types to kill an enemy with this shouldn't be that hard,Good Luck :)

Here's a list of the Weapons & Ammo Types as well as a small guide in how to activate/select them:

NORMAL WEAPONS:
(Selected by holding down & then flicking the in the direction of the weapon you want.
E.g: To select the Pistol you press & hold down the & then press )

Pistol +
Shotgun +
Machine Gun +
Minigun +
The Last Normal Weapon is the Minigun & that is found in Level.6. "Jungle Rip"
(This should be the last thing needed for the achievement so given that you have used all weapons & ammo types the achievement should now pop,NOTICE that by use I mean killed someone with every weapon/ammo,it's not enough to just fire the weapons)

SPECIAL WEAPONS:
(These CAN NOT be kept & are only picked up until you either Drop them,Change Weapon or Run Out of Ammo. NOTICE that if you drop them on the ground for too long they will disappear so make sure to get at least one kill before dropping them)

Rocket Launcher
Laser Rifle
Flamethrower
Grenade Launcher
The Last Special Weapon is the Grenade Launcher & that is found in Level.5. "The Betrayal"

AMMO TYPES:
(Selected by holding down & then flicking the in the direction of the ammo you want. Several types of Ammo can be used at the same time. Once an Ammo Type has been "Turned On" it will stay on even when you run out of ammo so as soon as you collect that Ammo Type it will be used again. You "Turn Off" the Ammo Type the same way you "Turn it On".
E.g: To select the Electric Ammo you press & hold down the & then press )

Electric Ammo +
Homing Ammo +
Incendiary Ammo +
Armor Piercing Ammo +
NOTICE: That Ammo Types need to be collected before they become available to use.
The Last Ammo Type is the Homing Ammo & that is found in Level.5. "The Betrayal"

EDIT:
Should you (LIKE ME) have failed to use one of the Special Weapons & the achievement doesn't pop once you reach & use the Minigun in the start of Chapter.6 "Jungle Rip" then simply exit the game & go to the menu & use "Mission Select" to jump to whatever chapter you think you might have made the mistake in...in my case it was the Rocket Launcher in Chapter 1 that I had tried to save for a time when I really needed it & by doing so it disappeared while it was placed on the ground & therefore I never actually got a kill with it so make sure to actually GET A KILL WITH ALL WEAPONS/AMMO TYPES. Good Luck