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Get Mk II weapons at a Weapon Workshop
A documented route is Bunker ownership → Mobile Operations Center with a Weapon Workshop (or combined Weapon & Vehicle Workshop) → convert an eligible weapon at its workbench → buy available components. If you already have a Weapon Workshop elsewhere, check that first.
The 12 Mk II conversions are Pistol, SNS Pistol, Heavy Revolver, SMG, Assault Rifle, Carbine Rifle, Special Carbine, Bullpup Rifle, Combat MG, Pump Shotgun, Marksman Rifle and Heavy Sniper. Conversion and Bunker research are separate: some components are sold directly, while others require a research unlock before purchase.
Sources
- GTAV Title Update 1.40 (opens in a new tab)13 June 2017: Mobile Operations Center workshop configurations and Mk II weapons
- Rockstar: six more Mk II conversions (opens in a new tab)New Content: six Mk II additions. Weapon changes: Heavy Sniper explosive damage to players/NPCs reduced; no current one-shot thresholds inferred. Historical Avenger property requirement excluded.