Well after doing a lot of editing the first thing you would want to do is hit it with an X-form reset. Before you do that set your objects backface cull to on.
Thanks FrankieV, but I have looking in maya and I have found a “solution”.
I select for example the mag with bullet, made an Edit Mesh → Extract (this don’t break smoothing groups) and after that I can use bind Skin and that works