Counter-Sniped Achievement in Halo: The Master Chief Collection

Fortunately, the achievement’s description here is quite self-explanatory. Load up a Custom Game on Bloodline with at least one other player. When the match begins, each player should pick up their Sniper Rifle on the top of their home base. Once you have the weapon, meet up anywhere on the map and have one player zoom in with their Sniper Rifle while the other player gets a quick headshot, thus unlocking the achievement. When the second player spawns, simply return the favor. Keep in mind that you must kill the enemy who was zoomed in with a Sniper Rifle or Beam Rifle, as no other weapon will count towards this achievement.