A really good way to help figure out the scale, rotation & position of your model is to import the rifle template that comes with the addon. It'll show you where on the grid your model should be in order to get it in relation to the unit's hands, how big your gun should be, what direction it should face, and how it should be set up in terms of hierarchy. To import one go ZE Tools/ZETools/Weapon Tools/Templates, and then pick the rifle template and hit "Import Template". That should help you figure everything out, hopefully.

I got the gun ingame ! Thank you everyone !!!! Now I just need to texture it and tweak it a little. (Bet you I'll have to ask a question again soon) Edit: well like I said I still have some questions and one problem. I setup the gun just like the rifle template showed me, but ingame the gun is pointing to the right (See pic) And also some Faces of the gun are missing ingame, is that because the gun is held wrong ?
And one question, how do I do the texture ingame ? I need a tga, right ? And in the msh I have to add the tga name ? If I get the gun right and with texture, I would be really happy and through this thread I'd have future references

Edit: Got the gun pointing in the right direction, but the gun is still missing some faces. Is that maybe because it's not texture yet ?