Here is the full list of all 36 Snipers achievements worth 1,000 gamerscore. It takes around 20-25 hours to unlock all of the achievements on Xbox 360.
Succeed at all the challenges from level 3.
Succeed all Level I challenges.
Reach the highest rank (Commander).
Kill multiple enemies with an explosive.
Win a match on each map for each game mode.
Win a game in each game mode.
Win a Contract match.
Purchase all equipment.
Purchase all Abilities equipment.
Be promoted to Lieutenant I.
Win a Last Team Standing game.
Kill an enemy with a silencer.
Win a Capture the Flag game.
Purchase all Booby traps equipment.
Purchase all weapons.
First weapons purchase.
Purchase all Scope equipment.
Succeed a Level III challenge.
Win a Team Deathmatch.
Kill an enemy caught up in his grappling gear.
Win a game on each map.
Destroy an enemy explosive.
Be promoted to Sergeant.
Purchase all Projectiles equipment.
Finish off an enemy who has been stunned by a stun grenade.
First equipment purchase.
Stab an enemy in the back.
Stab an enemy to death.
Win a Free For All game.
Kill an enemy by sending his own grenade back to him.
Kill an enemy through a wall.
Kill an enemy and yourself with a grenade.
Kill an enemy with an explosive.
Kill an enemy with a headshot.
Finish the tutorial.
First use of a Drone.