You may be correct. It’s just another “mouse gun” as far as I can see. But since an M4 is basically a short-barreled M-16 why keeps him from making that conversion? The receiver is the NFA controlled part and since he had to get all sorts of permission to get that what difference can a shorter barrel make?
Oh, sorry. I forgot we were talking about the government here. Logic isn’t really welcome, is it?
There’s more to the M4 than just being a short-barreled M16 - enough that the military gave it a different designation.