To install with OpenIV you replace the provided w_pi_pistol and w_pi_pistol_mag files these two places: 

GtaV\mods\update\x64\dlcpacks\patchday8ng\dlc.rpf\x64\models\cdimages\weapons.rpf
GtaV\mods\x64e.rpf\models\cdimages\weapons.rpf

If you have issues with not seeing the gun then replace the w_pi_pistol files in the other patchday folders.

Thanks for downloading.