All Fallout 4 Unique Heavy Weapons

Ashmaker

Variant Of: Minigun
Location: Potential reward for completing the quest The Big Dig

The Big Dig Quest
The player character receives the quest after talking to a woman named Bobbi No-Nose in a backstreet at Goodneighbor. She says that she's planning on breaking into the Diamond City strongroom located under the mayor's office. At first the player character needs to go down in The Dig, a tunnel starting at Bobbi's house basement and help diggers fight mirelurks. After, she asks the player character to meet her in Diamond City and help free another member of the heist team, Mel.

Freeing Mel can take one of several forms: bribing the guard nearest to him, pickpocketing a key, setting the protectron behind him loose to kill the guards, or passing a moderate or hard persuasion check. It may be difficult to find the right guard as there are no distinguishing characteristics. Breaking him out with lockpicking will likely result in security becoming hostile. To the left of the cell is the office, inside steal the key from the desk, then sneak to the right side of the cell. When the guards are not looking unlock the cell with the key and meet Mel outside. If the guards spot you they will become hostile.

Finally, the team goes into the tunnel, traveling through old metro stations and basements filled with feral ghouls and more mirelurks. Mel will frequently express his doubts about the tunnel actually leading to Diamond City, as the team is heading too far South. After they make it to a cavity underneath the strongroom and blow the ceiling with the help of Sonya, a modified eyebot, it is revealed that it's not Diamond City's strongroom but a secluded storage room owned by John Hancock, Goodneighbor's mayor.

The room is filled with the mayor's henchmen. The player character should be subsequently given the choice to persuade Bobbi to leave and surrender, kill all the guards and stay with Bobbi, or betray Bobbi and kill her for the mayor instead; if the player character enters the room wearing headwear incorporating a targeting hud, Fahrenheit and her man will be automatically hostile, forcing the PC to kill them to continue. If you still have the headwear on after finishing the quest by getting paid, Bobbi will also immediately turn hostile and attack.

If the player character persuades Bobbi to leave or betray her, Fahrenheit will reward them with a legendary minigun with incendiary bullets (+15 fire damage); Ashmaker. Additionally, John Hancock will become available as a follower.

Even if the player character kills Fahrenheit and sides with Bobbi, Ashmaker can be looted from her corpse and John Hancock will still be available as a follower after finishing Hancock's follow up quest of killing Bobbi.

Video: https://www.youtube.com/watch?v=thpfbmPTYig

Big Boy

Variant Of: Fat Man
Location: Sold by Arturo in the Diamond City market

Cost is 12,300 caps

Video: https://www.youtube.com/watch?v=prgFactLAYo

Broadsider

Variant Of: Broadsider
Location Reward for completing the quest Last Voyage of the U.S.S. Constitution

Last Voyage of the U.S.S. Constitution Quest
1. Head to the USS Constitution (East of Bunker Hill). As you approach the ship, the Lookout will meet you and tell you to head up into the ship and meet Captain Ironsides on top of the USS Constitution.
2. After talking to Captain Ironsides, scavengers will attack and you will need to deal with them. (OPTIONAL: Fire the Cannons). Hitting the robot allies with stray fire will result in the entire crew turning hostile and therefore failing this quest; however the cannon are safe to fire as they do not affect the robots.
3. Talk with Bosun on the third deck inside the USS Constitution.
4. He will ask you to repair or replace 3 power cables inside the ship. (It requires INT 3+ to repair the power cables or grab the power cables to repair them) (OPTIONAL: Grab power cables).
5. Return to Bosun and talk with him again.
6. He will ask you to repair or buy a replacement power relay coil.(It requires INT 5+ to repair the power relay coil).
7. Next, you will need to find Mr. Navigator and offer your assistance.
8. Mr. Navigator will ask you to recover the guidance chip for the ship from the scavengers.

Acquiring The Guidance
1. Head back towards Bunker Hill and talk to Mandy Stiles. At this point you will have to at least claim to choose to help the scavengers to destroy the robot crew or side with Captain Ironsides. Both paths follow the same pattern, but with a few differences. (Note: some companions such as Robert Joseph MacCready, John Hancock and Cait dislike it if you say you choose Ironsides, and other companions such as Codsworth like it).
1.If you side with the scavengers, they give you the guidance chip for free and ask you to bring them any equipment the ship requires so they can sabotage it, but warn you not to double cross them.
2.If you side with Ironsides, you'll have to steal the chip from the scavengers camp (there is a mercenary who stands in the room where the chip is, crouch behind the desk to the left you can remain hidden and steal the chip). (Note: some companions such as John Hancock, Preston Garvey, Codsworth and Piper dislike you stealing the chip).

Stealing the guidance chip will turn the local scavengers hostile, if spotted. Leave any companion out of sight, use a stealth boy, and leave through the chained door in the room containing the guidance chip for a good chance to successfully burglarize the scavengers undetected.
1. Head back to the USS Constitution and install the guidance chip on the main deck.
2. Now return to Mr. Navigator and talk with him (he should have moved up onto the main deck beside where you installed the guidance chip).
3. Mr. Navigator will now ask you to repair or retrieve the Poseidon radar transmitter, which is located beside Mr. Navigator and beside where you installed the guidance chip on the main deck. (It requires INT 9+ to repair the radar transmitter or you can retrieve a replacement from Poseiden Energy Turbine 18-F, North West of the BADTFL regional office. You may also be sent to the Poseidon Reservoir, south of Fort Hagen, to retrieve the replacement part.
4. After repairing the guidance systems, talk to Mr. Navigator again and he will tell you to talk with Captain Ironsides again.
5. He will ask you to retrieve FLL3 turbopump bearings from a specific location. Known locations for this part of the quest are: the Corvega assembly plant South of Lexington, Fort Hagen at the West edge of the map, and General Atomics factory northwest of The Castle.
6. Return to the USS Constitution and head into the captains quarters on the second deck, then install the the FLL3 Turbopump Bearings.
7. Return to Captain Ironsides on the main deck and talk to him, while doing so the scavengers will attack the ship again, eliminate them. If you let them get to the top deck you will fail the quest so a quick save is recommended before doing this part.
8. Head back up to Captain Ironsides, and he will reward you with the Broadsider and ask you to complete a final task of firing up the auxiliary power to launch the ship.
9. Activate the auxiliary power circuit and watch the ship take off. Quest complete after the ship crash.
10. If the player character reaches the tower in which the ship crashes (using two elevators on the east side of the ship at ground level), Ironsides will name you honorary lieutenant and grant you use of the captain quarters as well as the Lieutenant's hat.

Siding With The Scavengers
There is no difference between siding with Ironsides or the scavengers up until you are told to get and install the guidance chip and radar transmitter, as is mentioned above.
1. Once you retrieve the FLL3 Turbopump Bearings, take them to Mandy instead of Ironsides. Davies will sabotage them so that the ship will explode when the rockets are fired up.
2. Install the Turbopump Bearings and talk to Ironsides again. Go ahead and agree to turn on the auxiliary power.
3. After the rockets fail the ship will remain landlocked and the robot crew will turn hostile. Storm the boat with the scavengers and defeat Ironsides.
4. Meet up with Mandy after claiming the ship - she has wandered away to near Cabot House - to find out the scavengers held a vote and are not going to split the cut with you and have, in fact, voted to kill you.
5. Regardless of what dialogue option you choose the scavengers must be defeated to complete the quest. NOTE: They seem to be very slow to turn hostile if they turn hostile at all, and there's only four of them (one on the ship, one by the scavenger claim, Davies, and Mandy).

Video: https://www.youtube.com/watch?v=HHP7sI9FXTc

Death From Above

Variant Of: Missile Launcher
Location: Sold by Teagan on the Prydwen after reaching the rank of Paladin in the Brotherhood of Steel

Cost is 2,200 caps

Video: https://www.youtube.com/watch?v=3xO3z6XvnEA

Final Judgment

Variant Of: Gatling Laser
Location: Carried by Elder Maxson; available during Airship Down or Precipice of War or Rockets' Red Glare

It is carried by Arthur Maxson during the quest Airship Down. If you are currently siding with the Minutemen and you want to obtain this weapon without siding with the Brotherhood of Steel, just continue the Railroad quests until you receive the quest Precipice of War, but do not go to Police Station. Instead go to The Prydwen, and kill Elder Maxson in order to receive Final Judgment.

Alternately you can still acquire the weapon after completing Precipice of War by continuing with Rockets' Red Glare; engage the Brotherhood of Steel members in the main deck area, plant the explosives, and then you should get ambushed by Maxson and two unnamed Brotherhood of Steel members (one will have power armor and a Gatling laser) as you exit the Prydwen via the command deck. Be prepared as they'll open fire as soon as loading completes, there's very little cover available, and the energy weapons can deplete your health very quickly.

Maxson also uses it during The Nuclear Option.

Video: https://www.youtube.com/watch?v=q0rysS1etuA

Junk jet

Variant Of: Junk Jet
Location: Located in ArcJet Systems rocket control room

In ArcJet Systems on the table in the rocket control room. Accessing the room requires accessing a terminal that needs Advanced hacking to crack, however, the Sole Survivor can find a way to access this terminal without having to hack it. Found during the quest Call to Arms. If you have Nick Valentine as a companion he will unlock the terminal for you.

Dropped by Manta Man in a random encounter.

Video: https://www.youtube.com/watch?v=cJBOlZv8dBk

Partystarter

Variant Of: Missile Launcher
Location: Sold by KL-E-0 in Goodneighbor

Cost is 15,500 caps

Video: https://www.youtube.com/watch?v=ZHTC6gwCDJE

More Fallout Guides

All Fallout 4 Unique Melee Weapons: http://imgur.com/gallery/Phe9Q

All Unique Ballistic Weapons In Fallout 4: http://imgur.com/gallery/j8MZa

All Fallout 4 Unique Energy Weapons: http://imgur.com/gallery/7Kpzd

Fallout Easter Eggs You Missed: http://imgur.com/gallery/MoSX4

Fallout 4 Companion Backgrounds & Locations: http://imgur.com/gallery/APCsF