Never Saw it ComingG 15

If you missed some of the other earlier opportunities you have a very easy opportunity to get this late in the story mode. If you're like me you kinda struggled to put yourself in a position to get the achievement.

After you kill Olivia Marcano you can access a supply room containing body armor, adrenaline and a weapon locker with an M-14. There's another door in the room, and you can hear one of the Marcano's goons on the other side. This is an excellent opportunity to kick open the door and spray down the enemy on the other side.

I already had the achievement by this point but this is a very easy, very hard to miss opportunity to unlock it. If you want to make it even easier, turn aim assist to "High" before kicking down the door. At close range the assist does the aiming for you so you can't miss.