While most tutorials revolved around modeling require a complete model, the deletion of faces are necessary when creating an FPS weapon since one side will not be seen for the majority of the time.  Deleting certain faces add in lowering the poly count aiding in the FPS and overall poly count.  Creating a normal map and or using baked textures of a higher poly version helps to refine the overall look of the weapon itself.  Here is a low poly revolver without the higher poly portion but with the most essential parts deleted.