The Rimfire Report: HK91 Conversion Kit – It Shoots .22LR

    Welcome back to another edition of The Rimfire Report! This ongoing series is all about the rimfire firearm world and its various guns, ammo, sports, and mysteries. Today we have a sort of guest article from Nicholas C and his HK91 conversion kit to shoot .22LR. According to the HK fans, this was another form of training for the German military. The alternative was blue training plastic ammo but that is for another time and article. Let’s dive into this .22LR conversion kit for the HK91.

    HK91 @ TFB:

    HK91 Conversion Kit

    H&K actually made the HK91 conversion kits for the HK G3. However, there is a difference between the G3 and HK91 conversion kits. HK fans claim that the HK91 conversion kit is a lot less common than the HK G3 conversion kit.

    The bolt on the HK91 conversion kit has a 2-inch extension welded to the rear. When you pull the charging handle, it moves the bolt rearward. But since the .22LR bolt is shorter than a normal HK91 bolt, if you pull the bolt too far back, it will move past the hammer and get stuck behind the hammer. Apparently, the full-auto trigger pack for the HKG3 does not have this problem since the auto sear keeps the hammer down. And when you run the semi-auto bolt on an HK91, the bolt does not move back far enough to get behind the hammer.

    HK91 conversion bolt next to regular bolt

    HK91 .308 bolt on the left, HK91 conversion bolt on the right

    See the 2″ extension above?

    The 2″ extension will hit the end cap before the bolt can get behind the hammer. If you have the HK G3 conversion kit you can simply cut a 2″ rubber hose/tube to achieve the same results as the HK91 conversion bolt.

    The HK91 conversion bolt works similarly to a CMMG .22LR conversion bolt. The carrier is not the part that moves but instead there is a smaller bolt that moves when the gun is fired. The bolt has dual extractors.

    See the part my thumb is holding back? That is the smaller .22LR bolt. The rest is the carrier and only moves when you pull the charging handle.

    Both the bolt and barrel are date coded IA which stands for ’80 or 1980. They are also serialized and have proof marks.

    The HK91 conversion kit consists of a drop-in bolt and barrel adapter. It is an 18″ long sleeve that slides down the factory .308 barrel. The wider chamber part has a steel ring that acts as a friction lock so the barrel does not slide back under recoil.

    I am using an EBO SAR8 overstamp HK91 clone as my host gun for the HK91 conversion kit. The previous owner removed the muzzle device. You can see the conversion kit barrel goes all the way to the end of the muzzle.

    The HK91 Conversion kit comes with two magazines.

    They are painted gray and have a .22LR magazine inserted into them as you can see in the diagram above from the owner’s manual.

    Shooting The HK91 Conversion Kit

    The manual had this about aiming with the factory iron sights.

    For shooting 50 meters, you use the 200-meter diopter rear sight. Rotate the rear drum to 400 meters for shooting 100 meters. I tried this at the range and it worked like a charm.

    I filmed the HK91 conversion kit in high speed and to my surprise, the brass ejection happens a lot faster than I expected. Watch the video. The brass is ejected but watch how long it takes for the bolt to close.

    Here is a video by my friend Scott aka Machine-gun Dad on his conversion kit for his full-auto G3.

    Final Thoughts

    The .22LR conversion kit for the HK91 is a cool piece of kit. They used to be only a few hundred dollars but since they are long since discontinued their prices have increased as their demand has increased over time. According to some HK fans, the HK91 conversion kit, like the one I have, is more rare and therefore fetches more money. An HKG3 conversion kit is around $1,000 while the HK91 version can be as much as $1,500. Thanks for reading along and I hope you enjoyed learning about this conversion kit.


    Nicholas C

    Steadicam Gun Operator
    Night Vision & Thermal Aficionado
    Flashlight/Laser Enthusiast
    USPSA competitor

    Any questions please email him at [email protected]