Both Barrels

From Halopedia, the Halo wiki

Both Barrels

Both Barrels is an achievement for Halo: Reach multiplayer matchmaking added with the Noble Map Pack. The achievement was unlocked by earning a Double Kill with the shotgun. It is represented by two crossed shotguns over a double kill icon.[1]

Following the shutdown of Xbox 360 Halo online services on January 13, 2022, this achievement is no longer attainable.[2][3]