need help whit materials

First of all hi to all who is reading . i have a little isue whit materials since iam not good at making atlas i made a several textures on 1 objectes for instance my thomson submachine gun has 2 textures on it and when i import the 3d object to unity my model is just grey ... i cant see the texture i also packed all files including textures into blend file whitch in the end was exported as FBX file but still no texture any help ?