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The Complete Reference on the Legal NFA Conversion of HK Firearms

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The Complete Reference on the Legal NFA Conversion of HK Firearms
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HKPRO SPECIAL FEATURE: The Complete Reference on the Legal NFA Conversion of HK Firearms

Note from HKPRO: This would be a good time to grab a cold drink, and to sit back, relax and read the most comprehensive article ever written on the legal conversion of HK firearms to full automatic. Thomas T. Hoel of Tactical Advantage, the author, has graciously granted permission for the reproduction of the article here, along with the best periodical for serious firearms enthusiasts, Small Arms Review. The articles as reproduced below were originally published in the April, May and June, 2000 issues of SAR, as a three part series. This is part of my commitment to you to keep HKPRO the most comprehensive source of information on all things HK.

The Mechanics of the Heckler & Koch NFA Conversions

By Thomas T. Hoel
Photos by James Bardwell, Tom Hoel and Dan Shea


With the Civilian NFA Weapons collecting market in a continual stage of flux, one thing remains constant. Those firearms of the general type almost universally known as “H&K” models remain THE most favored and desirable amongst those collectors of firearms of the “modern”, post World War II era. Their almost mythic popularity and desirability are not without pitfalls however, as unless one is well versed in what is available in terms of the mechanics and cosmetics of the available versions, it can come as a rude awakening to discover what one has acquired is not necessarily what one expected! The fact that these guns, as a class, are some of the priciest civilian legal semi-automatics makes it incumbent upon the owner, or individual considering ownership, to grasp the many significant factors that determine relative value of the vastly different incarnations of these guns. With very few exceptions, those “H&K” type machine guns available for civilian purchase as fully transferable Title II NFA weapons all began life as Title I semi-automatics. This the basis for the most confusion, as there were many different routes taken to convert the guns into functioning selective fire full-automatics. These converted semi-auto guns are often surrounded by confusion and misunderstanding, and it is that problem that this article will address in detail.

Factory HK33E machine gun showing push-pin, swing down type of trigger group attachment.

Even the common identifying term of “H&K” is a misnomer since an examination of the history and pedigree of this general firearm design will reveal that the salient features of its’ design were well established during the late WWII years in the work of the famous Mauser-Werke firm on the evolutionary prototype Sturmgewehr-45. Only after a period of considerable movement around continental Europe post-war did this basic design eventually find a permanent home with the reconstituted pre-War Mauser factory in the guise of the then new West German firm of Heckler & Koch GmbH, and its’ ultimate final conversion to the then new NATO 7.62mm caliber. This occurred, after having been initially designed and experimentally first produced in post-war Spain by the Government entity CETME during the period 1949-1956, with the engineering guidance of Ex-Mauser-Werke employees who had fled Post-War Germany and settled in Spain. After a hurried initial adoption of the new rifle in 1957 by both the Spanish and West German militaries, the Spanish and West German Governments co-operated for a time on the final development and perfection of the basic operating system until it became clear that there existed differing requirements for a new service rifle in each country. Development had begun in Spain not only because the prominent ex-Mauser-Werke engineers were presently residing there, but also because West Germany had initially adopted the also then new FN FAL rifle as the Gewehr-1, the “G1" FAL. Only when it became quite clear that FN-Herstal was not going to allow a production licensing agreement to take place, allowing for West German production as opposed to direct contract purchase from FN, (...owing to a lingering bitterness over NAZI Germany’s roughshod run over Belgium) did the West German Government begin in earnest a search for a suitable equivalent rifle design that could be domestically produced. The differing specifications extant in Spain and West Germany by 1963 caused termination of the second joint-development agreement and ultimately resulted in the production of two similar, but different versions of the perfected original CETME 7.62mm NATO caliber Modelo “C” rifle design. The CETME produced versions issued to the Spanish military were in a slightly different form than the now ubiquitous German Army standard Gewehr 3, or “G3" as it became universally known. Parts and fittings were not fully interchangeable, though fundamentally similar.

That Heckler & Koch has become synonymous with the particular mechanical design type is due more to that firm’s aggressive marketing and promotional strategies, than any original conception of the design parameters. Although since the pre-War Mauser-Werke firm resurfaced as H&K GmbH, there were no doubt a multitude of significant individuals still on hand from the time of it's wartime conception, and the return of the original engineering team to West Germany from Spain/CETME no doubt cemented HK GmbH as the preeminent production facility of this design weapon. It goes without saying too that H&K GmbH has considerably mined the potential for expansion within the basic design parameters in the ensuing years, producing a vast family of mechanically similar weapons. Clearly this potential is owed in large part to the soundness of the original concept which allowed an inherent capacity for expansion into differing calibers and applications.

So for purposes of discussion, when we talk about an “H&K” type firearm we are using that term in the general sense, an even more important distinction when it is known that there have been more than a dozen countries which have produced guns to the “H&K” military pattern(s) since the mid-Fifties, with a few even producing guns in the semi-automatic configuration for intended sale to law enforcement or civilian markets worldwide where such sales were lawful. “H&K” type guns made by H&K GmbH licensees to the pattern of the semi-automatic versions made and marketed by the West German firm in the U.S.A. have also been imported here in substantial numbers over the years. Imports of these semi-auto versions were clones of the HK91 .308 caliber rifle and came from Greece (Springfield Armory SAR-3/SAR 8) and Portugal (FMP XG3S; various importers). H & K GmbH had the sole honor of manufacturing, and offering for import through their U.S. based sales and marketing arm, HK U.S.A., Inc., civilian legal sporting guns in the .233 Remington and 9mm Para calibers with their models HK43, HK93, HK94, and their “pistol” version gun, the SP89.

Foreign Licensee production and importation of semi-automatic sporting arms was limited to the .308 caliber class weapons, the “HK91" clones. No COM-BLOC 7.62x39mm M43 caliber sporting weapons were ever imported into the U.S.A. by anyone, though H&K did catalog a few versions of their guns in that caliber for military sales. (NOTE: as this article was being prepared it appeared as though a new U.S. based concern, Special Weapons LLC, has obtained ATF approval to begin manufacture and sale of a “U.S. made” version of the HK91 & HK94 type semi-auto Sporting rifles using receivers manufactured in the U.S.A., with other major components obtained from foreign Government Licensee producers of HK type weapons, together with enough U.S. manufactured minor components to qualify the guns as being “Made in the U.S.A..” according to the new Import restrictions currently in effect. The information available seems to indicate that these new made receivers will be close copies of the original design, though not identical in all respects)