The following is from memory of other articles and remembrances, I make no claim that I am right but this is what I "THINK" he is going on about
Pre 1982 Macs were open bolt, ATF changed their interpertation of what a MG, this administrative change made these Macs MG's. Because of the original open bolt mac design it was considered easy to modify to shoot full auto. But instead of confiscation they grandfathered all the pre 82's and all guns produced from then on fired from a closed bolt.
I think this Examiner article has key portions left out in the quoted sections.
The way this article is written sounds like it was passed through an anti-gun filter. None of these so called "unregistered MG's" have select fire capacity. They are simply more easy to
illegally convert to an unregistered mg. These are no more "unregistered machine guns" than my shoelaces.....
I believe this is full text of the ATF Rul. 82-8. with attached download link from atf.gov
"ATF Rul. 82-8
The Bureau of Alcohol, Tobacco and Firearms has reexamined firearms identified as SM10 pistols, SM11A1 pistols, and SAC carbines. The SM10 is a 9 millimeter or .45ACP caliber, semiautomatic firearm; the SM11A1 is a .380ACP caliber, semiautomatic firearm; and the SAC carbine is a 9 millimeter or .45ACP caliber, semiautomatic firearm. The weapons are blowback operated, <b>fire from the open bolt position with the bolt incorporating a fixed firing pin,</b> and the barrels of the pistols are threaded to accept a silencer. In addition, component parts of the weapons are a disconnector and a trip which prevent more than one shot being fired with a single function of the trigger.
The disconnector and trip are designed in the SM10 and SM11A1 pistols and in the SAC carbine (firearms) in such a way that a simple modification to them, such as cutting, filing, or grinding, allows the firearms to operate automatically. Thus, this simple modification to the disconnector or trip, together with the configuration of the above design features (blowback operating, firing from the open bolt position, and fixed firing pin) in the SM10 and SM11A1 pistols and in the SAC carbine, permits the firearms to shoot automatically, more than one shot, without manual reloading, by a single function of the trigger. The above combination of design features as employed in the SM10 and SM11A1 pistols and the SAC carbine are normally not found in typical sporting firearms.
The National Firearms Act, 26 U.S.C. § 5845(b), defines a machinegun to include any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.
The "shoots automatically" definition covers weapons that will function automatically. The "readily restorable" definition defines weapons which previously could shoot automatically but will not in their present condition. The "designed" definition includes those weapons which have not previously functioned as machineguns but possess design features which facilitate full automatic fire by a simple modification or elimination of existing component parts.
Held: The SM10 and SM11A1 pistols and the SAC carbine are designed to shoot automatically more than one shot, without manual reloading, by a single function of the trigger. Consequently, the SM10 and SM11A1 pistols and SAC carbines are machineguns as defined in Section 5845(b) of the Act.
With respect to the machinegun classification of the SM10 and SM11A1 pistols and SAC carbines, under the National Firearms Act, pursuant to 26 U.S.C. 7805(b), this ruling will not be applied to SM10 and SM11A1 pistols and SAC carbines manufactured or assembled before June 21, 1982. Accordingly, SM10 and SM11A1 pistols and SAC carbines, manufactured or assembled on or after June 21, 1982, will be subject to all the provisions of the National Firearms Act and 27 C.F.R. Part 179.
[ATFB 1982-2 49]"
http://www.atf.gov/publications/download/p/atf-p-5320-8/atf-p-5320-8-appendix-b.pdf