Scattered throughout the levels are white barrels that look like the ones in the achievement. Surely enough, if you shoot one enough, it will explode.
Now, an easier way to do this achievement other than blind luck is to get 1-3 more players with you. Kill off any AI survivors before doing this. Start the campaign on any level until you find a barrel or two. Next, position a player near the barrels until a Hunter comes along (turn on subtitles to know when one is around). Step away from the player near the barrels and the Hunter should pounce on them. Shoot the Hunter a few times with an automatic weapon, then blow up the barrels. The Hunter will die, and you should obtain the achievement.