HLMV recognizes my model incorrectly

[Bors_Balog]

I want to make a AA12 in gmod however, when I want to view it in Half life Model Viewer, some of the gun's side's appear to be facing the wrong way

https://files.facepunch.com/forum/upload/383380/4152df68-2b09-4deb-99a3-7b2ca5d42eba/image.png

https://files.facepunch.com/forum/upload/383380/105d5b37-fa42-43ae-90a6-135ec97d6c91/image.png

all the sides that cannot be seen can be seen if viewed from the other side
I have made the textures in Blender however it looked normal there

If anybody knows what can be the problem or how to fix it, please tell me.

[Grodbert]

Most likely it's the normals that are flipped on the wrong side, it looks good on blender because it's displayed on both sides (I think) so the faces that are flipped in the wrong direction are still shown, on the source engine it only displays one side unless you specify it on the .QC of the texture.

To fix it go back on the model in blender, select all faces (in edit mode) with A and then press CTRL+N to recalculate all normals, it also gives you the option of having them facing inward of outward, you can check the little box to see the difference, normals that are flipped inwards usually appear darker as the light is not reflected as well.