Mass Effect 2

Everything Nemesis wrote is right; just wanted to add that the M-920 Cain has to have 100% ammo to fire. Otherwise will just light up and do nothing.

* Spoiler Free *

Resumed : Collect all heavy weapon ammo upgrade and '' Kill enemies with 5 different heavy weapons during the game''

The easiest way to get this achievement is to have access to a DLC, the M-490 BLACKSTORM PROJECTOR, with this you could get the 5 different weapons as early as you get the collector heavy weapon on the mission to protect a certain colony.

If not, you will have to optain multiple ammo upgrades for heavy weapons to unlock the last one.

As soon as I start my second playtrough I shall write down here where you can find thoses upgrades. (You get one at the beginning)

The order you get the weapons are :

M-100 GRENADE LAUNCHER
ML-77 MISSILE LAUNCHER
M-622 AVALANCHE
Collector Particle Beam
M-920 CAIN

This achievement requires you to kill 5 enemies with 5 different heavy weapons, there is a total of 8 heavy weapons, 3 of which are DLC. You should already have one heavy weapon kill before you meet the illusive man, this is because before you go down the elevator Miranda tells you to use the M-100 Grenade Launcher to destroy the mech's that are coming through the door.

A second easy heavy weapon kill is the M-451 Firestorm, you can acquire this weapon through natural progress of the Zaeed loyalty mission.

A third easy heavy weapon kill is using the arc projector if the arc projector dlc has been downloaded, This weapon will be unlocked as soon as Shepard acquires the Normandy SR2

A fourth heavy weapon kill could be using the ML-77 Missile Launcher, this weapon can be acquired from the Normandy research station after one heavy weapon ammo upgrade have been researched, The ML-77 Missle Launcher requires 5,000 iridium.

A fifth heavy weapon kill could be using the M-622 Avalanche, this weapon can be acquired from the Normandy research station after two heavy weapon ammo upgrades have been researched, The M-622 Avalanche requires 15,000 iridium.

A sixth heavy weapon kill could be using the M-920 Cain, this weapon can be acquired from the Normandy research station after three heavy weapon ammo upgrades have been researched, The M-920 Cain requires 25,000 iridium.

A seventh Heavy weapon kill could be using the collectors particle beam, this weapon can be acquired during natural progression on Horizon
The last heavy weapon kill could be using the M-490 Blackstorm Projector, this is a preorder dlc weapon which cant be acquired any other way, If the player has the weapon it will be available once Shepard acquires the Normandy SR2.

All the above information is correct. I would like to add that to get a kill with the M-622 avalanche you have to fire two to three times on a enemy. One shot only freezes the enemy. Another shot or two with the Avalanche will kill them. This is what held me up on this achievement.