This is my Rifle, This is my Gun
From Halopedia, the Halo wiki
This is my Rifle, This is my Gun is an achievement in Halo 4 and Halo: The Master Chief Collection. It is awarded when the player carries a UNSC weapon all the way through the third campaign level, Forerunner, on Heroic or harder. The achievement is worth 20 Gamerscore in Halo 4 and 10 gamerpoints in Halo: The Master Chief Collection. It is represented by an MA5D Assault Rifle and an image of the map Solace in the Xbox art.
The name of the achievement is a reference to the military chant which states "This is my rifle, this is my gun; this is for fighting, this is for fun," with each mention of the "gun" accompanied by a crotch grab. The chant is notably featured in the film Full Metal Jacket.