Thank you for downloading the 'Black&White Auto-Shotty'. For this to work, extract all the contents of 'Black&White Auto-Shotty' to the directory as seen below.

C:\Program Files\Steam\SteamApps\<Your E-Mail>\counter-strike source\cstrike\materials\models\weapons\v_models
C:\Program Files\Steam\SteamApps\<Your E-Mail>\counter-strike source\cstrike\materials\models\weapons\w_models

Good luck.