American-Made Replica of 9x39mm OTs-12 Rifle

    American-Made Replica of OTs-12 9x39mm Rifle (1)

    It was less than a year ago, at SHOT Show 2018 when Wolf Ammunition officially introduced the legendary 9x39mm Soviet/Russian cartridge to the US market. Although it is a really interesting and capable round, there are not too many firearms made in this caliber yet because there are several obstacles such as getting the dimensions of the cartridge (as of now, its drawing can’t be found in SAAMI or CIP standards), finding proper barrel blanks, ordering custom reamers and gauges and so on. However, as you have guessed from the title of this article, there are people in the industry who despite the mentioned issues managed to build firearms chambered in 9x39mm.

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    Daniel Fisher, an employee of R&D department of KNS Precision, is the designer of the weapon that is the subject of this article. He started this project with the purpose of building a replica of a Russian OTs-12 “Tiss” rifle which is an AK-based compact rifle chambered in 9x39mm. Now, this is a personal project and these rifles won’t be available commercially, however, I hope in future we’ll see them available for purchase. I’ve been following this project since its very beginning and today I am privileged to receive from Daniel an exclusive content consisting of images and description of the project which I used to put together this article.

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    The easy part of this project was probably the fact that the OTs-12 replica is based on the AK-47 which means that the majority of parts used in this gun are directly borrowed from the AK-47. The interchangeable parts include the front and rear trunnions, receiver, bolt, trigger mechanism etc. Nevertheless, despite a large amount of readily available parts used, this was not an easy project and involved a lot more than just building another AK. Many of the parts had to be designed and made from the ground up, others required to be substantially modified to work properly and some parts were really hard to obtain. Let’s take a closer look at the design of different parts of this weapon.

    Ammunition and Magazines

    Although the 9x39mm cartridge has the same rim dimensions and overall length as the 7.62x39mm and it can be used with standard AK bolts, it has a less case body taper which along with the larger 9.3mm bullet makes it virtually impossible to use standard AK magazines. I assume that it is possible to load several rounds into AK magazines and sort of make them work, but you won’t be able to load the standard AK magazines to their full capacity and make them properly work with the 9x39mm ammunition. The latter requires less curved magazines and more internal space in the bullet area. So from the very beginning of the project, it was clear that AK magazines won’t work.

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    VSS Vintorez magazines

    What Daniel did is he managed to get a set of 20 round magazines of the VSS Vintorez rifle that are designed for the 9x39mm cartridge. These magazines are very rare in the USA and quite expensive, too. However, as Daniel told me: “these are the only ones that really work reliably with this cartridge at the moment“.

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    Note the opened up magazine well

    Now, getting your hands on properly designed magazines still doesn’t mean you solved the feeding problem. It turns out that despite having a similar rock and lock design and using cartridges with identical rim and overall length dimensions, the VSS magazines have quite different external geometry compared to the standard AK magazines. In order to fit the VSS magazines into the AK receiver, Daniel had to modify the front trunnion, magazine catch and the receiver. By removing the material in proper amounts and in right places, he managed to make the VSS magazines work flawlessly in this OTs-12 replica project.


    Barrel

    If it was a more standard US caliber, then making the barrel for this project would basically be a matter of getting a rifled blank, chambering and profiling it. However, as mentioned above, the 9x39mm cartridge has a rather unique bullet and bore diameter of around .366″ or 9.3mm. Not having a barrel of a proper size would simply kill the project, because no matter how passionate you are or how dedicated you are to the project, the barrel is not something that you can make yourself unless you have access to some advanced machinery.

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    PTG 9x39mm chamber reamer

    The help to solve this problem came from the industry. Green Mountain Rifle Barrels made prototype 9×39 barrel blanks and provided them to Daniel thus making this project possible. The chamber reamer and headspace gauges were custom made by Pacific Tool and Gauge.


    Gas System

    This is definitely the most interesting part of the OTs-12 project. The gas system of this gun is quite unique and ingenious. And the reason it is different than the standard AK gas system is that it is quite challenging to design a gas system that would flawlessly work with such a large bore subsonic round. Here is how Daniel Fisher describes the gas system design issues associated with the 9x39mm cartridge:

    The problem with this cartridge is that it is subsonic and therefore lower peak chamber pressure. The larger bore size makes this problem worse as the larger the bore – the faster the pressure fall-off occurs, leaving you with low port pressure.

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    Although the described gas system of the OTs-12 replica could probably function with a standard AK (Krinkov) gas piston, Daniel used a KNS Precision adjustable piston to be able to adjust the gas system because he plans to experiment with supersonic 9x39mm loads.

    In the case of the AR-15 platform, you can relatively easily solve such an issue by relocating the gas port and gas block closer to the chamber and using a shorter gas tube thus shortening the gas system. However, it is not that easy in the AK platform. The too short gas system would require to shorten the bolt carrier which would possibly cause other issues related to the dwell time, mass of the reciprocating parts and recoil spring design. Obviously, the designers of the original OTs-12 faced this problem too and they found a quite an interesting solution. So Daniel used the same solution in his replica.

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    The gas system of this rifle consists of a gas port drilled quite close to the chamber, a primary low profile gas block mounted right next to the rear sight block, an AK gas block in its normal location and an AR-15 style gas tube that connects the two gas blocks. When the round is fired, the gasses are vented from the gas port into the rear gas block and start traveling forward through the AR-style gas tube towards the AK gas block where the gasses are finally released and hit the piston of the rifle. At this point, the rifle cycles as a regular AK. The reason such a complicated system is developed is the need to vent the gasses at a point where the bore pressure is higher and keep them pressurized for a longer time to have a sufficient dwell time.

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    The AK (Krinkov) gas block is installed in a usual location but the barrel underneath it has no gas port.

    To make the rear gas block, Daniel used a low profile AR-15 gas block which he modified to make it fit under the original AK gas tube. Then he used the straight portion of the AR-15 gas tube to make the gas tube that connects the front and rear gas blocks. Lastly, he modified a JMac Customs GBC-13 gas block to accept the connecting tube.

    Overall, this gas system proved to be successful perfectly cycling the action with the commercially available subsonic 9x39mm Wolf ammunition both with and without the use of a suppressor. Particularly, it was tested with Dead Air Silencers Wolf-9SD and Ghost-M suppressors.


    Furniture

    As you can see in the images of this article, Daniel actually built two 9x39mm OTs-12 replicas with different furniture. Daniel’s own gun is the one that has a Midwest Industries Krinkov aluminum railed handguard. He had to modify the handguard to make it fit the Sabrewerks KOP rear sight block.

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    Daniel made this project in collaboration with Tyson Wahrmund who is also a KNS Precision employee. The version with wooden furniture is Tyson’s rifle. In order to fit the wooden furniture, they had to modify the upper handguard and attach the lower handguard retainer directly to the gas block.

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    Both versions have triangle folding stocks. The classic version has a bakelite original AK grip whereas the more modern iteration has a Magpul pistol grip.


    Markings

    Although both rifles are semi-auto only, they marked the receivers with Cyrillic letters seen on select fire AKs … for the sake of coolness! The logo on the front trunnion represents the combination of the Izhevsk triangle with the skunk of the Lockheed Martin Skunk Works Program.

    The Cyrillic model designation on the receiver stands for OTs-12M. The “M” at the end of the model name is used in the same manner as the Soviet Union used to designate the “Modernized” versions of firearms. You can see that “M” at the end of model names of firearms like the AKM, PKM, AK-74M, PMM etc.

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    The Cyrillic words on the trunnion stand for Battle Buddies after the line of morale patches designed by Tyson Wahrmund.

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    There you go! Another fascinating AK project. To me, this project is not only interesting because of the design challenges and the ways they found solutions, but it is also a great example showing how the companies and individuals in the industry collaborate to support and make such a cool project happen. Great job!


    Many thanks to Daniel Fisher for the provided information and images!

    Hrachya H

    Being a lifelong firearms enthusiast, Hrachya always enjoys studying design, technology and history of guns and ammunition. His knowledge of Russian allows him to translate and make Russian/Soviet/Combloc small arms related information available for the English speaking audience. Hrachya also writes for SilahReport.com
    Should you need to contact him, feel free to shoot him a message at [email protected]


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