Mortar and Mourning is the mini-game available after buying Mourningwood Fort when it becomes available as real estate. Score 2,000 points to earn the Kaboom! achievement as well as a random legendary weapon. Scoring over 2,000 points is also a requirement for unlocking augmentations on the Swift Irregular and Simmons's Shotgun rifles. Achieving this can be very difficult (many random variables involved), there is no simple answer that will allow it to be completed quickly beyond patience, luck and tenacity.