Weapon Workshop

The Weapon Workshop is an optional modification feature in Grand Theft Auto Online, added as part of the Gunrunning update and further updated in the Doomsday Heist Update.

Grand Theft Auto Online
The workshop is dedicated to weapons customization and is operated by the Weapon Mechanic.

It can be added by purchasing the optional upgrade to the appropriate cargo bay in the Mobile Operations Center, the Avenger, the Terrorbyte, or the Kosatka. Hiring the Mechanic (working as the Weapon Expert) for the Arena Workshop will include a workshop space for him. One is also added to the lower level of the Arcade upon choosing a gunman for The Diamond Casino Heist; this is the only one available at no cost. One should also note that the workshop will be removed upon completion of the heist.

The Weapon Workshop basically consists of a long workbench with several tools on the wall, with a Heavy Sniper in the middle on a weapon vice presumably undergoing the customization process. Racks of weapons and ammunition are shown on the wall to the left and right of the tool rack in the middle.

Grand Theft Auto Online
"Well, welcome to the candy store. You don't look like someone who's going to be... satisfied with something off-the-shelf,[sic] We got that in common. I hate shelves, bad things, shelves. Anyway, you wanna cook up something a little special for these special times? I'm your man."

- Chester McCoy, first time accessing MOC Weapon Workshop

Selected weapons can be upgraded into Mk II variants, which offer an array of customizations not present on their standard models, including ammo types, unique attachments and aesthetic options (liveries and colors).

Gunrunning weapon upgrades unlocked by the corresponding research can be applied here. The same applies to the ones added in the Doomsday Heist Update, except for the unique options not listed in the research. Note that upgrading a weapon allows the user to switch back to the base weapon and switch back again to its Mk II equivalent for free, although base weapons may reset their attachments.

Restocking any special MKII ammunition (Incendiary, FMJ, Armor Piercing, Explosive, and Hollow Point) requires a visit to the workshop while normal MKII Ammunition can be bought from the interaction menu.