Both this Achievement and The Man In The High Tower Achievement can be earned at the beginning of the level Heat.
To earn the Achievement Four Of A Kind you must headshot 4 enemies in a row. An easy way is by using the M21 sniper rifle at the start of the level to attack the first group of enemies being ambushed.
To earn the Achievement The Man In The High Tower you must find the RPG stash in the church tower & attack enemies with the RPGs while in the tower.