This tutorial assumes you have the cod toolbar already set up in Maya 8.5 and that your model is textured and UV mapped!
Note this is the way i do but it might not be correct!
So after you build your model you will need to do a few things before it will work in game.
You will need to apply colour white because if you leave it the way it is with will come up black in-game and you wont be able to see your texture. to apply the colour you go to Color > Apply Color and click the box.
make sure your setting are the same as mine and then hit apply color.
then hit the number 5 on your keyboard and your model should come up white.
Now to get a rig you go to "Activision\Call of Duty - World at War\model_export\american\weapons" and find a rig that is right for your model. for example i am going to use the thompson rig. for the viewmodel you use "usa_thompson_smg.VMGun" please note that any model with VMGun is the Viewmodel.
So now that you have two models its time to start deleting the thompson mode but you have to be careful not to delete the rig. Go to Window>>Outliner and select every that is not your model if you select J_gun deselect this because that is the bones we are going to need to rig the model. once you have deleted the model more then likely the joints will be hidden so go where i marked in the picture.
now all you have to do is drag the joint into there place like for example put Tag_flash into the muzzle because Tag_flash is where the muzzleflash effects are played.
now this is the tricky part binding the skin, you will need to have Outliner open and open select everything but J_clip and the model's clip like in the picture.
now while they are all selected go to Skin>>Bind Skin>>Smooth Bind and click the box
now click Bind Skin and you every part of your model should be pink except the clip!
now repeat that process for the clip.
select the clip model and the tag, go to Skin>>Bind Skin>>Smooth Bind and click the box, click Bind Skin and it should show pink.!
now go to the Call of Duty:World at War Tab >>Model Export
navigate to your weapon and add it then click Force Export Selected Joints
Now simply select every thing while the model export window is open and click Export Selected En and your done just add the material and .XMODEL_EXPORT file to assetmanger and you have a working weapon for you map/mod.
disclaimer - i did not make this model i got it from garrysmod all credit goes to the creator and i did not make the rig either they are supplied with the mod tools.