Regarding what you need in order to upgrade the gun, you can check the bottom part of the first comment, here:
http://www.wowhead.com/item=109168/shredirons-shredder&bonus=525#comments:id=2056248(the two items can also be purchased from other players and on AH)
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Also, if you want to upgrade the gun, the these are the two engineering crafted items you want to look at:
1st Schematic: True Iron Trigger which makes Unstable True Iron Trigger
2nd Schematic: Blackrock Rifling which makes Unstable Blackrock Rifling
Remember you can go to Tanaan Jungle and kill the NPC Driss Vile. He has a 35% drop chance of a ilv655 gun, and you can attempt this once a day.
The books you mention are
Secret of Draenor Engineering, right? That book you can create by using 5x True Iron Ore , and has a daily cooldown. Check your Engineering window and search for the spell:
Secrets of Draenor Engineering