Problem With Replacing Weapon

https://i.imgur.com/vIUdfcy.jpg

I encounter a strange problem with importing and exporting models with 3dsmax. Even without editing anything, simply exporting will mess up the meshes. Have anyone ever encounter this problem and know how to resolve it?

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December 29, 2017 update1

Okay, I understand what the problem is. It seems the cas exporter doesn't work with my version of 3dsmax 2013. There is no way I could make changes and export it back into the game.

Does anyone have a working copy of Max and can help me with some simple weapon swapping?

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December 29, 2017 update2

I figure it out, I fixed the problem.

https://i.imgur.com/k8GI0kk.jpg