The Patent behind the Heckler & Koch HK233 and HK237

    Technically Heckler & Koch haven’t really released the HK233 yet. It’s “just there” on their homepage and they forgot to tell the marketing department to send out the press release.

    But as we found out about the HK233 (5,56 NATO) and HK237 (300BLK) there were various people posting both in Facebook groups and at HKPro about the patent behind the rifle.




    “Patent” isn’t a language I speak, especially combined with German. I learned that a long time ago, but there were some very interesting drawings that made more sense.

    The patent from Heckler & Koch Gmbh was described as: “Adapter for mounting at least one additional device to a self-loading firearm, and equipped with this self-loading firearm”

    and furthermore:

    “The invention relates to an adapter (3) which is adapted for mounting at least one additional device (45) to a self-loading firearm (1), extends in weapons longitudinal direction, and having a tube side (25) and a housing-side (35) section. The adapter (3) is characterized in that it with one of its two portions (25; 35) on a holding device (79, 89) on the tube (19) or on the housing (4) can be fixed, and (with the other portion 25; 35) on the housing (4) or tube (19) by means of a longitudinally movable guide (96, 97, 109; 177, 179, 181) is movable storable. The invention also relates to a self-loading firearm (1) an adapter (3) according to one of claims 1 to 19, a holding device (79, 89) on the tube (19) or housing (4) for fixing the adapter (3), and a movable bearing on the housing (4) or tube (19) which is adapted to be longitudinally movable guide of the adapter (3).

    So this new patent is most likely HK’s solution to a problem that never officially existed (Source), but it’s fixed now with the HK233. The HK233 is a G36 Version 2. At least it’s one way of looking at it, I’m sure there are other ways.

    “If, for example, the tube emits heat to the housing during heat firing and expands or distorts it, which could occur, in particular, in the case of plastic housings, Or if the tube itself thermally warps, the additional device – largely because of the special adapter bearing – will be largely spared from tensions thus caused.”

    You can find the sources of the Patent here:

    and here:

    The pictures and figures are from the sources mentioned above.




    Look at the drawing above, N# 110. I think this design is interesting and worth discussing. If you look at the LWRC IC-A5 Individual Carbine the solution looks very similar, where you open or remove a lid to service the piston. There might be more rifles out there, with this solution?

    If you add the knowledge, that a few Special Units have left / are leaving / are transferring from the H&K G36 to the LWRCI it becomes a bit ironic.

    Here are two examples TFB recently reported about: and

    The below picture is from the LWRCI IC Manual.

    You can check LWRCI IC-A5 on the homepage for reference:

    I have never seen the HK233, but my question is how reliable is HK’s design?

    Will a laser (or similar) keep mounted on the lid keep it’s zero?

    That’s a question a lot of HK’s customers are going to ask themselves (or find out, too late).

    The parts are called “110 cover” and “119 hinge pin”, and by the looks of it I wouldn’t place a laser there.

    Note where LWRC put their front sight.

    You also get a very short line of sight with your back-up iron sights, you’re only using about half of the potential length.



    These list describe the content, and translated (from German) below. Yes, a machine translated it from German in case you some odd technical translations.




    1 Self-loading firearm
    3 adapter
    4 casing
    4a housing section
    5 buttstock
    7 grip
    9 Fire selector lever / safety lever
    11 deduction
    13 trigger guard
    15 magazine holder
    17 Cocking lever
    19 pipe
    21 Bayonet recording / grenade launcher connection
    23 Muzzle brake
    25 Pipe-side section
    27 Picatinny rail / top
    29 Picatinny rail / bottom
    31 breakthroughs
    32 Keyhole
    33 bridge section
    34 passages
    35 Housing-side portion of the adapter
    36 Pin / bolt
    37 recess
    38 groove
    39 Picatinny rail / rail
    40 Recess for folding grain in Picatinny rail
    41 Folding grain arrangement
    42 Passages for bolt / pin for supporting the folding grain
    43 Camp for folding rear sight assembly
    44 Bilateral breakthroughs for storage of the folding rear sight
    45 optical sight
    46 Recess for folding rear sight in Picatinny rail
    47 Pin / pins
    48 folding rear sight
    49 Holes in the adapter for hinge pin

    50 rails
    51 Recesses for bolt
    52 Sloping rear end
    53 mouth
    54 guide extension
    55 bearing section
    57 bearing section
    59 Groove for defining the bayonet receiving
    61 Groove for determining gas consumption
    62 gas purchases
    63 bearing section
    65 Federation for gas purchases
    66 bearing section
    67 Groove for sleeve
    69 pipe Length
    71 relief grooves
    73 Stege
    75 Fastening bolt / pin for receiving bayonet
    77 Fastening bolt / pin for gas consumption
    79 shell
    81 passage
    83 transverse groove
    85 tube nut
    87 elongated tube nut
    89 Sleeve extension section
    90 ring groove
    91 Fastening bolt / pin
    93 hinge section
    95 Longitudinal recess for cocking lever
    96 Counter-profile socket
    97 Non-locating counter profile
    98 deepening
    99 tube support
    101 longitudinal recess
    103 Orientierungsausnehmung
    105 bolt
    106 bolt
    107 Orientierungsausnehmung
    109 Dovetail extension
    110 cover
    112 breakthrough
    113 Picatinny rail / rail
    115 passage
    117 support web
    119 hinge pin
    121 Camp for folding rear sight
    123 mold insert
    125 shaped spring
    127 locking lug
    129 recess
    131 recess
    133 camp
    135 recess
    137 web
    139 saddle
    141 longitudinal section
    143 guide nose
    145 transverse groove
    147 passage
    149 bolt section
    151 spiral spring
    153 Chamber
    155 firing pin
    157 gas well
    159 Gas piston rod
    161 Tangentialstift
    163 bolt head
    165 against Steg
    169 Gas piston rod guide
    171 Gas piston rod spring bearing
    173 Gas piston rod spring
    175 Extension gas piston rod guide
    177 Separate non-locating counter profile
    179 Wedge-shaped groove
    181 Slit-like groove

    End of Patent.

    I have very little experience with the G36, but I do have experience shooting rifles fairly successfully. And I have a lot against the design which is now repeated in the HK233:

    You have a barrel. On top of this barrel you mount a piston and a charging handle. On top of the piston you put more metal (or polymer), then you add some sort of carrying handle where you put your optic. On top of the optic you put another optic. Yes, I’m aware that all G36s don’t come with optics like pictured below, but even with a normal specification you have a sight line which is very high above the bore, and you are forced to compensate a poor design with cheek welds.

    You don’t have to build a skyscraper to build a rifle.

    The G36C shows what I mean. I’m sure it goes bang every time, but there’s room for improvements in other areas to make it easier to hit the target.


    G36C, with lots of extras above and under.

    Eric B

    Ex-Arctic Ranger. Competitive practical shooter and hunter with a European focus. Always ready to increase my collection of modern semi-automatics, optics and sound suppressors. TCCC Certified medic.