M92S SBR

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  • HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    I've been AWOL from MDS for several months now... Let's just say I've been busy. Had no time to breathe, let alone post (or shoot, or build). Anyway, for the first time since before Christmas, I had time to disappear into the basement for a full day, and finish (mostly) a gun that's been sitting in a tray, broken into parts, and waiting for a trip to the blasting cabinet and parking tanks...



    The gun started as a demiled parts kit from a brand new M92 pistol (had to do it that way since I got this before the gun was on the roster). I built it on a receiver flat that I folded, welded, fitted, hardened, tempered, blasted, and engraved. (see http://www.mdshooters.com/showthread.php?t=161803 for a discussion of how I hardened the receiver - the video in post 12 of this thread is the receiver for this gun!) The rear end is the Asian copy of the Russian/Bulgarian triangle side folder. The grip and safety switch is from the new SAM7's. The barrel is also new because the factory barrel's machining was so bad that it was unsalvageable.



    The muzzle device has the interior cone removed to make it MD compliant (no folding stock and FH). I may still make something custom there, but I just don't have the time now. :(



    A couple of acknowledgments before the pictures: 1- Thanks to the great folks at Engage Armament for sourcing the parts kit, helping with the engraving, and introducing me to the AK platform. 2- Thanks to Jim Fuller and Rifle Dynamics for bringing their awesome AK Builder class to Maryland. It was this class that gave me the knowledge and confidence in the AK platform which culminated in this build. To anyone thinking about taking the class: I highly recommend it!



    Without further introduction, here is my new M92S SBR:



    EDIT: Scroll down to posts 9 and 10 for more pictures and a discussion of a couple interesting issues I ran into during the build.



    ImageUploadedByTapatalk1430001516.315018.jpg

    ImageUploadedByTapatalk1430001528.038089.jpg

    ImageUploadedByTapatalk1430001541.195016.jpg

    ImageUploadedByTapatalk1430001556.001795.jpg

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    ImageUploadedByTapatalk1430001583.782620.jpg

    ImageUploadedByTapatalk1430001594.803865.jpg
     
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    HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    I thought that I would document some of the issues that I encountered when building this. This is my 4th AK build on a homemade receiver (8th if you count commercial receivers, and guns I've helped friends build), and by far the most complex. It was not an easy road.

    First, the front trunnion was in spec... just not in spec compared to the AKMs that I am accustomed to. It is very different from every other modern AKM around. It is actually closer to the front end of the original milled AK-47s than to a AKM. In particular, the bottom of the trunnion is about 4x thicker than an AKM. That necessitated milling a substantial pocket out of it to get the front side folder latch in the correct location (in addition to drilling the hole for the pivot pin).

    ImageUploadedByTapatalk1430082635.576697.jpg
    ImageUploadedByTapatalk1430082656.567898.jpg

    Further, the notch in the trunnion that accepts the front stud on the magazine is a couple millimeters further back compared to an AKM. Picture next to Polish AKM.

    ImageUploadedByTapatalk1430082684.000719.jpg

    That meant that magazines would hit the center support and not lock into place! The solution was to drop an end mill through the mag well and mill a small flat on the center support.

    ImageUploadedByTapatalk1430082740.193696.jpg

    This is actually what they do to the factory guns (see pic below for factory center support still in the receiver shard)... Something that I only noticed after hitting this issue. In retrospect, I probably should have salvaged the factory center support and used that. But my solution seems to work ok. I have some minor concerns that this will turn or deform with heavy use... I doubt it will (since the factory piece doesn't turn), but it's possible. If it does, I'll replace it with the factory center support and tack weld it to prevent turning. But I suspect that I am worrying about nothing.

    ImageUploadedByTapatalk1430082755.367739.jpg

    Second big issue: the factory barrel. What a disaster! I'll start from the chamber and move towards the end.

    1- the extractor relief cut looks like it was cut but a drunken blind machinist. I don't even know how this is possible!

    ImageUploadedByTapatalk1430082778.312521.jpg

    2- the barrel journal was totally wrecked by being shoved in without being aligned (I know that's the cause because I did it once :( ).

    ImageUploadedByTapatalk1430082830.336942.jpg

    3- the barrel pin hole looked like it was drilled with a piece of rusty rebar.

    ImageUploadedByTapatalk1430082841.893445.jpg

    4- the lower hand guard retention notch was machined at a slight angle... Resulting in this:

    ImageUploadedByTapatalk1430082855.233046.jpg

    5- the gas block/front sight journal was machined too small. Factory solution: Beat the journal with a center punch to displace some material so it can be pressed on.

    ImageUploadedByTapatalk1430082882.663283.jpg

    With all of those issues, I just decided to replace the barrel. I found a good price on a nice chrome-lined part, and am very happy with it.

    (To be continued in next post)
     
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    HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    Third, the safety. I bought a safety from the SAM7SF because I love how it works. Of course, I wasn't thinking that the M92 uses a completely different style safety that is not interchangeable (without looking really out of place).

    ImageUploadedByTapatalk1430083064.469488.jpg

    Thus, I had the file and drill the stock safety to interface with the SAM7SF switch. Of course, it also required milling a L shaped slot in the bottom of the receiver... I patterned my cut off of my SAM7SF. I screwed up in milling this slot a little (made it too wide), but the handgrip covers my mistake nicely.

    ImageUploadedByTapatalk1430083078.261802.jpg

    A couple notes about the safety install: (i) unimpeded operation of the safety required relieving the left side of the rear trunnion and the bottom of the rivet "biscuit" ... you can barely see it in the picture. (ii) I doubt this would work with a standard hand grip nut... it would probably get in the way and would definitely deform the receiver. The M92's use of the riveted hand grip nut allows this to work. (iii) I had some concern about the cuts weakening the receiver in the back, but when I considered that within less than an inch, there was support from the rear trunnion and support from the riveted hand grip nut, I decided it would be ok... only time will tell. It may also help that the receiver is made of stronger 4130 chromoly, rather than the factory 1050 carbon steel.

    Fourth, the top cover hinge: I don't like that this is permanently installed by the factory by peening a pin over. I bought a factory replacement (damn hard to find), but then decided to make the hitch pin pictured on the gun, secured with a mini split ring. I made it a very tight fit to keep the rear sight steady. I will monitor this to make sure there are no problems with wandering zero. If there are, I will go back to the factory solution.

    ImageUploadedByTapatalk1430083092.701706.jpg
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    Fifth, populating the new barrel... What a royal pain! The problem is that everything depends on everything else. It's almost too complex to explain, so I'm not going to try. Just take my word that it's much harder than a standard AKM. I got everything right on my third try. :(

    That's all for now.
     
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    HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    Thanks to all for the kind words. :)

    Well, that's certainly better looking than the last time I saw it!


    That was a while ago... Before thanksgiving, I think. Thanks for the help with getting the engraving done on this!
     

    HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    Finally got time to burn this baby in... If there's a problem, I'm going to find it in the next couple hours.

    Off to the range.

    ImageUploadedByTapatalk1430672050.483172.jpg
     

    HT4

    Dum spiro spero.
    Jan 24, 2012
    2,728
    Bethesda
    600 rounds before I got tuckered out and went home. The gun ran like a champion. Zero malfunctions of any kind. The only casualties of the day were my bruised shoulder, a pair of nice sunglasses, a burnt left hand (forgot my gloves), a scorched wood shooting bench (this gun got very hot!), and the neon yellow paint on the front sight post (burnt off within 200 rounds).

    ...and I don't think that I made any friends at the range. This gun is not quiet.

    More on the gun to follow once I tear it down and do a thorough inspection.
     
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    awptickes

    Member
    Jun 26, 2011
    1,516
    N. Of Perryville
    The only casualties of the day were my bruised shoulder, a pair of nice sunglasses, a burnt left hand (forgot my gloves), a scorched wood shooting bench (this gun got very hot!), and the neon yellow paint on the front sight post (burnt off within 200 rounds).

    ...and I don't think that I made any friends at the range. This gun is not quiet.

    More on the gun to follow once I tear it down and do a thorough inspection.

    It's awesome to finally see it finished.

    And I know the problems of bringing an SBR'd AK to the range... But it's a nice tool to get people to back off when they're shooting too close to you. (Those nets between lanes on Hap Baker don't block the sound of a 223 with a brake.)

    I too discovered that paint burns off of the front sight on an AK. I melted a bunch of paki-tape once too.
     

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