You are using 77 colors. Why?
I made a rough edit for you.
33 colors (still too much)
That pale pink-brown doesn't seem to be working very well for you. It'd probably be beneficial for you to have a few colors dedicated to the color of the wood. When someone sees that group of colors they'd instantly assume it's wood, assuming you shade them similarly. The metal parts look very very flat. The scope should look like a cylinder atop the gun instead of a weird shaped block. also shouldn't the eye piece be more symmetrical?
The stock and furniture of the weapon are suffering from pillow shading. After looking at a reference it seems you've squished the clip and the trigger together. The clip would probably be bigger.
Summary:
-Define those forms.
-Cut that color count down.
-Use and post a reference.
