install here: Grand Theft Auto IV\GTAIV\pc\models\cdimages\weapons.img\

you must download these gun models for the textures to work:
https://www.gtagaming.com/grims-weapon-packs-in-gta-iv-f5407.html (volume III/M14)
https://www.gtainside.com/en/gta4/weapons/149317-glock-34/