its legal becasue its not a whole weapon. you can ship almost any thing in parts just not ready to use out of the crate

That's totally false! Parts of weapons can be, and are regulated in much the same way complete guns are.

Unless you disassemble the gun completely, in such a way that each part is unrecognizable by customs (which is impossible for certain parts, like upper receivers) then they will just get seized like everything else.

haha, just the same situation as I had when I moved back 6 monthes ago. I dissembled my M4 and sold all the others. My plastic M4 receiever was taken away at customs.

You can bring your gearboxes, motors, basically everything that doesn't look like a gun IIRC, which basically means you'll have to replaces bodies and that's about it.

+1