Unlock Xbox Live Gamerscore points, by completing the following Achievements.

Achievement	How to unlock
Bloodbath ( 15 points )	Achieve a "Bloodbath" Kill streak.
Chapter Brother ( 10 points )	Complete a mission in co-op mode.
Chapter Master ( 40 points )	Play through each mission with two different Space Marines.
Devastator ( 20 points )	Complete a mission without using melee.
Emperor's Champion ( 10 points )	Earn a gold Aquila in every survival challenge.
Exterminatus ( 15 points )	Kill 5000 enemies in total.
For the Emperor! ( 20 points )	Get over 50 kills with each weapon type.
Honour in My Shield ( 20 points )	Complete a mission without dying.
Master Your Craft ( 10 points )	Use a special move.
Relic Bearer ( 10 points )	Find all the collectables.
Tactical ( 10 points )	Unlock all weapons and ability upgrades.
Victory for the Chapter ( 20 points )	Defeat the Warboss!