Dave_G: I believe you are mistaken.
US v. Miller's conclusion was the Supreme Court requesting that a lower court issue a finding of fact on the issue of a short barreled shotgun being a useful militia weapon or not. The text of the Miller decision indicates that if the SBS were found to be a weapon useful to the militia, it would be protected under the Second Amendment, but the finding of fact was never made, as Miller had died by that time. A newly manufactured, fully automatic M4 would be useful to the Army, as they have purchased new machine guns in such a configuration after 1986. Thus, it would seem that US v. Miller would protect the manufacture of a post-86 machine gun by a non-SOT.
Kharn