To unlock the Unloaded trophy in RAGE 2, you will need to fire a total of 70 bullets from an Assault Rifle within 16 seconds.
You can do this very early in the game when you pick up an Assault Rifle as part of the story. The Assault Rifle doesn't need to be upgraded. Simply reload the weapon so that you have a full clip of 35 bullets and hold
. Once the clip is empty, you will automatically reload, so just continue holding
until you have used two full clips.