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Legal Parts Count

My goal is to configure the SL8 in the G36 base configuration with G36 magazines.  I've been researching the parts count problem since the TN conversion relies on US-built magazines to achieve the total parts count for 922 compliance parts count quota.

The parts count must be maintained, as supported by this document from ATF:

   

SO... we have to play the parts count game.

I did some research because there is some conflicting information out there.  The parts count for the G36 base model configuration APPEARS to be 16 parts.  All references to the TN conversion indicate that if G36 mags are used, then two other parts - besides the four parts provided by the conversion - need to be allocated.

The breakdown from my research indicates the following parts apply (highlighted in GREY)

 - the TN conversion parts are highlighted in RED:
 - the home-built US parts are highlighted in GREEN:
 - the US HK SL8 manual number is listed in BOLD after the name:

Total Parts
(1) Frame, receiver, receiver casting, forging or stamping:  1
(2) Barrel:  2
(3) Barrel extension: n/a
(4) Mounting block (trunion): n/a
(5) Muzzle attachments (brake, flash hider, etc.): n/a (on original SL8 configuration)
(6) Bolt:  25
(7) Bolt carrier:  38
(8) Operating rod:  7
(9) Gas piston: 6 
(10) Trigger housing: 
(11) Trigger: 62 
(12) Hammer: 54 
(13) Sear: 59 
(14) Disconnector:  68
(15) Butt stock: 47
(16) Pistol grip: 47
(17) Forearm/hand guard:  83
(18) Magazine body: 84 
(19) Magazine Follower :  85
(20) Magazine Floor plate:  87
 

= 16 parts (caveat - see below)


Opinion differs on these items, subject to an official interpretation from ATF:

  • Barrel Extension (Lugged end of the breech in receiver - the "metal part"?)
  • Trunion (same?)

    The part in question is molded into the composite stock and is inherently unable to be removed as a separate part.  In comparison, an AK trunion is mechanically attached to the receiver via rivets and can be counted as a separate part.  Furthermore, the HK manual does not define the part as an individual part and there is no part number for this "part".  The removal of the "metal part" of the receiver would in fact irreparably destroy the connection between the two parts.  Thus, the part should in fact be counted as "one" part by the ATF's standards that have been applied to other firearms.

    The locking nut, while not identified in the HK manual, is in fact a locking nut and not a "trunion (aka mounting block)".
     
  • Operating Rod 

    There are two opinions on the Operating Rod.  Either way, an argument can be made that "either/or" applies and thus a part can be counted.  Logic would suggest the push rod is the operating rod.  Given this, the "FAL charging handle loophole" should not be applicable:
     
    •  Op Rod driven by gas piston - part #7 in the HK SL8 Manual:

      The short-stroke piston sets the gas piston against the "piston rod" or "push rod" (as per the HK manual, it is called by both names).  Technically, this is called a Tappet.  A tappet is normally categorized as an "operating rod" by ATF definitions.  Whether or not the tappet (or push rod) on the SL8 is considered by ATF to be a "parts count" part is undecided.  If this is compared to similar designs such as an SKS or Steyr AUG, then it should be counted as a compliance part.
       
    • Charging Handle = Operating Rod ? 

      The ATF made themselves a loophole and defined a FAL Charging Handle as an Operating Rod... (!!!) ...sad but true.  If the same "logic" is applied here, then the "piston rod" (see above) is not an Operating Rod.  This is HIGHLY UNLIKELY, but I wish to document this nonetheless.
       

    To reiterate the point, an Operating Rod most certainly exists on the SL8/G36 system.  "+1" on the parts count... 17 now...
     

  • Disconnector

    The US HK manual does not mention a disconnector in the parts list.  The SL8/G36 system uses a sear-based action.  A disconnector exists in the system, listed as item #68, which in the manual is labeled as "Locking lever".  The "locking lever" serves to catch the hammer at the end of its rearward motion after the carrier pushes it downward to reset the firing mechanism.  The trigger must be released to "unlock" the hammer before the sear can be engaged again.
     
  • Trigger Housing

    The original HK SL8 butt stock design, and the TN conversion, both prevent an HK G36 select-fire pistol grip/trigger housing (aka "trigger pack") from installation.  Both designs accomplish this by molding the pistol grip and the lower receiver section as one piece.  This part should be self-canceling in the parts count because the only part that is available is a US-built part (via the TN conversion).  In other words, there are no G36-styled US-built trigger housings. 
     

There is one omission in the manual - there is a part that is numbered, but not labeled. This part is #71 in the manual. This is a spacer (or slide?) for the safety lever.

Bottom line, the jury is out until someone writes ATF for verification.  There could be AS MANY as 17 parts which assumes a build based on the "classic" military-style G36 design that includes a flash hider (or muzzle brake).  I plan therefore to err on the side of caution and install enough parts to meet 17 parts "just to be sure".  Legal compliance is my goal!  ;)

Again, my target build is to be the "classic" G36 standard rifle profile.  That means I'm adding a flash hider.

Therefore, to achieve the goal of "no more than 10 imported parts", my particular build must find 3 US parts elsewhere after the TN conversion is installed.  My current plans are to manufacture some of the following parts in the shop:

  • Operating Rod/Piston Rod (UPDATE - manufacture is complete - see link here)
  • Flash Hider
  • Magazine Floor Plates
  • Magazine Followers

I haven't figured out the final tally on which I will build.  Someone has already built followers and floor plates from scratch and the op rod is a relatively simple job on the lathe.  I should be able to build the FCG components via work with the mini-mill.  A surefire fore grip is another option I may consider.  We shall see! 

Update 3/06 - I made an operating rod and it fits quite well!  See link here...  One part down...