Old Guns

Old Guns is a quest and achievement/trophy in Fallout 4.

Quick walkthrough
Quest Can be Received from Preston Garvey in Sanctuary at a certain point in the game. Alternatively, a few days after you secure The Castle, when you tune to Radio Freedom you will hear the radioman and Ronnie Shaw asking for your presence in The Castle, which will also begin the quest. After receiving the quest, head to The Castle and talk to Ronnie Shaw. She'll guide you to the old General's room where you need to use the Workshop (i.e, be in Workshop mode) to clear the rubble. Inside, you'll find a turret and Sarge. Sarge will boot upon seeing the player, giving a few seconds to land a couple of power shots to weaken him before the battle begins. He is devastating in stand-and-fight combat, even against power armor, and can sprint at a very high speed to ram and crush his opponent. He can have difficulties crossing the narrow door entrance, so if he gets stuck it is a good opportunity to spam him with (pulse or nuka) grenades. If he gets through, it is a good opportunity... to reload the game.

After defeating Sarge, open the door with the button on the wall and take the Artillery schematics.

Make the Artillery, assign somebody to it, and throw an Artillery smoke grenade in the target location.

Starting the quest
Quest Can be Received from Preston Garvey in Sanctuary at a certain point in the game. Alternatively, a few days after securing the castle, you will be approached and engaged in conversation by a woman named Ronnie Shaw, she tells you of the old Castle's untapped armoury. After some dialogue, the Old Guns quest will begin and Ronnie will lead you to a large hydraulic steel door within the Castle, she will tell you that this door is not accessible and you will need to find another way round. Ronnie then leads you inside the Castles halls into the old General's office where a hallway (now blocked by rubble) leads to the Armoury.

Lower Halls
Ronnie Shaw will ask you to clear the rubble, using the workshop, the lone survivor can clear said rubble and gain access to the lower halls/rooms leading to the armoury. Inside are a few rooms with general junk. Also minor defence such as mines and a mk V machine gun turret. Guarding the entrance is and heavy sentry bot called Sarge (Fallout 4), who will instantly attack you. After defeating him, you can go into the room before the armoury. Inside you will find a computer with the last generals, General McGann, last entries and also, his corpse. You will need then to go through the door to the West Bastion.

West Bastion
Ronnie Shaw will access a computer that will open the armoury. Inside is an array of plunder, including an artillery schematic and some artillery smoke grenades, which are needed for the next part of the quest. After taking the schematic it will add an artillery gun to your workshop. Speak to Ronnie, she will ask you to build some artillery guns and assign someone to them. After doing this, speak to Ronnie again and she want to test the new big guns out.

Testing the Artillery Guns
Ronnie Shaw asks you to keep the Minuteman radio station on (optional task) and to throw a grenade into the test site. If you have the radio station on, Ronnie will speak to you via it, once you approach the test site, throw an artillery smoke grenade into the site and step back. After a few seconds the guns will fire and Ronnie will tell you the test was a success. After this, speak to Preston Garvey and complete the quest.

Quest stages

 * 1) Return to the Castle
 * 2) Speak to Ronnie Shaw at the Castle
 * 3) Gain access to the Castle's armory
 * 4) Talk to Ronnie Shaw
 * 5) Build and assign artillery at the Castle
 * 6) Talk to Ronnie Shaw
 * 7) Follow Ronnie Shaw
 * 8) Head to the target area
 * 9) (Optional) Keep your radio on and tuned to Radio Freedom
 * 10) Throw a smoke flare into the target area
 * 11) Speak to Preston Garvey

Bugs

 * This quest may cause the transmitter for Radio Freedom to stop broadcasting (Operator complains of lack of power even if ample power is provided).
 * Tuning into Radio Freedom after throwing the smoke grenade may cause the broadcaster to leave his post and refuse to return.
 * The artillery may fail to fire after throwing the smoke grenade, completing all other quest objectives without triggering the "Speak to Preston Garvey" objective, rendering the quest unbeatable.
 * If you start the quest after having already retrieved either the artillery blueprints or smoke grenades (via console commands, etc), you will not be able to progress. However this can be fixed by adding the smoke grenades to your inventory if you do not have any.
 * Minuteman NPCs dead, unable to set someone to man the artillery.