Aim for the Head
Aim for the Head is an achievement in Halo: The Master Chief Collection. It is unlocked by earning a total of 2,500 Headshot medals in multiplayer; this includes both matchmaking and custom games. Spartan Ops missions are considered custom games, and can be used to very quickly earn hundreds of headshots. The achievement is worth 10 gamerpoints.
Players attempting to unlock the achievement should avoid playing Halo 3 multiplayer matches, as the Headshot medal is not awarded in Halo 3 multiplayer matches (due to the fact that the Headshot medal was only awarded in campaign in the original game) - the only game in the collection for which this is the case.