double_barrel_shotgun_v.2.zip

This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • Double Barrel shotgun <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• Double Barrel shotgun/
  • info.txt
  • lua/
    • weapons/
      • DBS_weapon/
        • shared.lua
  • materials/
    • models/
      • weapon/
        • V_dbs/
          • V_dbs.vmt
          • V_dbs.vtf
          • Vshotgun_normal.vtf
    • rg/
      • rg_parascope.vmt
      • rg_parascope.vtf
  • models/
    • weapons/
      • v_dbsshot.dx80.vtx
      • v_dbsshot.dx90.vtx
      • v_dbsshot.mdl
      • v_dbsshot.sw.vtx
      • v_dbsshot.vvd
      • v_dbsshot.xbox.vtx

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