Jiggs' Loot

Jiggs' Loot is an unmarked quest in Fallout 3.

Detailed walkthrough
There are a series of secret codes hidden within access terminals around the Museum of Technology. This is part of a series of security tests for a scavenger, Prime's loot allocation for another comrade expected to show up at the museum. You only get one attempt at entering the codes. If you make an error, you will not be able to complete this quest and will be unable to obtain the Xuanlong assault rifle.

Although Prime alludes that he has left '...the usual breadcrumbs' for the player to follow, the clue is actually in Prime's name, as the correct numbers are all prime values (divisible by only themselves and the number 1, for example, 2, 3, 5, 7, etc.). Successfully unlocking all three terminals will grant the player the password for the Security Office terminal, allowing them to unlock the safe.

The first terminal is on the wall when you enter the museum. As soon as you enter the west wing, the second terminal will be on your immediate left (the second terminal to the right). The third terminal is on the bottom floor near the Delta IX rocket. The safe is located west of the planetarium in the security office that overlooks the Virgo II. The terminal codes are:
 * Terminal #001 - 19 (Ground floor, directly across from the entrance to the museum.)
 * Terminal #002 - 53 (In the museum's West Wing, which is past the Vault tour. Just after entering, seen ahead and a little to the left. The furthest terminal from you.)
 * Terminal #003 - 113 (Ground floor by the Delta rocket.)

Accessing any of these terminals allow you to begin this sequence.

Inside, the safe holds 200 caps, sundry other valuables, and the gun locker key for the planetarium office's cabinet. This cabinet contains several firearms, including a laser pistol or missile launcher and assorted ammunition (greatly varies, usually 3x assault rifles and a random weapon/ammunition). There is a Nuka-Cola Quantum on a shelf near the gun safe above the desk.

After entering the last terminal code, the player receives another note from Prime, Earned your share. In the note Prime tells his buddy to meet him at the "usual spot", the diner near Jury Street Metro station, which is marked on your map the moment you access the password. By the time you arrive, Prime is dead (lying on a table behind the counter), but is still worth finding. His corpse has 500 more caps, explosives, ammunition, and the unique weapon, the Xuanlong assault rifle.

Rewards

 * Xuanlong assault rifle
 * 700 caps (200 from Jiggs' loot, 500 from Prime's body in Jury Street Metro station).

Bugs

 * You can bypass all the hacking and lockpicking by hiding in the Planetarium and waiting for the 2 Super Mutants to start arguing in the middle. Once you attack them (keep trying to hide), they'll both run for the utility room to get the missile launcher even though they're not supposed to know about it and the locker is locked. Just make sure you snipe the one with the missile launcher before he hits you once they come out of there.
 * Sometimes unlocking the third terminal doesn't give you the password for the security office. Even after hacking the security computer you cannot unlock the safe. Reloading a save game from before you entered the Museum of Technology and unlocking the terminals in the following order circumvents this bug: 3/1/2.
 * Prime's empty body: after activating all the terminals and getting the note, Prime's body sometimes does not show up in its entirety (only a hand or foot) at Jury Street Metro, and whether or not the whole body is present, no loot is found on Prime. This bug is caused by another non-player character looting his corpse while you're away. On the PC, use the console and click the body (or body part). When Prime comes up at the top of the screen, type 'resurrect' and hit enter. Exit the console and blow his head apart, and voila - all the original loot.
 * In some cases, Prime's body does not appear at all in the diner. Instead, little pieces of him can be found outside, for example the nearby bus stop.
 * Sometimes, after getting all codes right, you will not see Prime's corpse, you'll only find some of his small organs. You can still loot him but he is hard to see.