Plutonium

YPCD and.. what the hell is that pfp bro..

Did you map the UV layout? Because PNG mapping is flat, so the game can't distinguish what is the stock or barrel of the gun.
skin base: weapon_acr_col.iwi

Use GIMP, is better for warping.

YPCD Could you send me the PNG?

YPCD You said you used Paint.net. It's great for simple edits, but terrible for this, as it doesn't have good warping tools. I recommend using GIMP.org. Use the original weapon_remington_acr_col.png file, the one you got from imgXiwi.
Create a new layer and paste the PNG onto it. Lower the opacity of the original texture layer to 35%. Use the Warp Transform tool.
click on the edges of the cammo in the reference to create a cage, and then drag the points so that your logo stretches and distorts to exactly match the shape. Export at the same resolution as the original, open run %LocalAppData% and go to /plutonium/storage/iw4 and create an images folder.

YPCD This whole UV warp thing is actually quite difficult, especially in Cod Zombies.

YPCD When I say "create a cage," I'm referring to a transformation tool: warp. Here you're using a reference image, for example, a cammo texture where the logo will go. You position points along the edges or important lines of the surface. You click and drag the grid points to stretch, shrink, and distort. You do this so that the PNG fits into the original space.

YPCD yes, exactly.

YPCD The original specular glow has a bluish metallic tone. When the diffuse color becomes too dark or uniform, the game applies this specular glow on top. The game is probably still using the weapon's original _spc.iwi file. Also, the whitespace you created in the _nml file is probably wrong; the normal map cannot be black or completely empty. The correct plane/whitespace is purple, a specific RGB 128, 128, 255.
So, extract it and edit it in GIMP as well, leaving it at 0,0,0 or use the same as you used in _col, create a new png with the color 128,128,255 and convert it back to _nml.iwi. Leaving it in black or white also messes up all the colors. Sorry for not mentioning this part too.

YPCD You only need one thing for the _nml file. Take your original weapon_remington_acr_nml.iwi file and drag it to imgXiwi.exe , it will become a PNG. Open this PNG in GIMP. In GIMP: Click on Colors at the top and select Colorize or simply Fill with color. Enter these exact numbers: Red = 128, Green = 128, Blue = 255. This will make the entire image solid purple. That's it. No extra layers. No black underneath. No changing the opacity. All 100% purple. Save it as a new PNG of the same size as before. Drag this new purple PNG back to imgXiwi.exe, it will become weapon_remington_acr_nml.iwi. Place this new _nml.iwi file in your folder: %localappdata%\Plutonium\storage\iw4\images\

YPCD If you don't have the iw4, use the iw5.