Close Quarters Combat
From Halopedia, the Halo wiki
Close Quarters Combat is an achievement in Halo: Combat Evolved Anniversary and Halo: The Master Chief Collection. It is awarded for having at least four sniper rifle rounds left at the end of the level The Truth and Reconciliation. In the original game it is represented by four sniper rifle bullets surrounded by a purple octagon; in The Master Chief Collection it is represented by a screenshot of Infinity (strangely, sharing its image with the That Just Happened achievement).
The Achievement is worth 25 Gamerscore in the original game; in The Master Chief Collection it is only worth 10 points.
Reaching the end of the level with at least four sniper rounds remaining should not be difficult for most players. A player running low can find one cache of sniper ammunition in the brig in which Keyes is being held, and a second cache is just outside the ship's bridge. Playing through the level with the Bandanna skull will completely eliminate the need to conserve ammo, so the player only needs to remember not to swap out their sniper rifle, something that should not be a problem as the sniper is, understandably, a weapon with no peers in the level.