-Stock is not extensible.
-Clip is independent and totally modeled.
-Details (shooting mode selector, charging handle, etc.) are static but can easily be detached for animation.
There may be some textures missing pop-up. Just reload them from the texture folder of the file.
I just saw there is some textures in the material editor that aren't used on the model (spec level and opacity bmps.). Delete the material, these maps are not included
For more photos of the check the item ID:432633
It's the same M4 model