HK 33 223 pistol build

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  • jdindadell

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    Figured I would photo document my latest HK build.

    Some of it will be specific to the HK/33/93 223 family, but most of it will relate to all of the various caliber HK roller guns.

    Building a pistol. 12.7 inch long barrel from RCM. The bulk of my parts are from a Malaysian military contract HK 33 kit that I bought from Apex a while ago. Flat is likely a Special Weapons flat (as those are the only flat made for the 223 guns, at least to my knowledge.) No 922r parts needed, as it is a pistol build. I will convert the lower (clip and pin) and convert the trigger box to semi only. only part substitute is the locking piece, a 16" barrel hk33 uses a number 3, where the 33k (a 12.7" barrel 33 with std rifle forearm) uses a number 8.

    1st up, bend the flat!

    Bending jig is the latest style that RTG sell. It can do all of the receiver sizes. Works well, have used it for 3 9mm and this 223 flat so far. The yellow tape is to stop the alignment pins from falling through the holes.






    Done! Well not really, but it looks good enough for a pic!!!

     

    jdindadell

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    So after bending, the rear of the receiver was a bit too tight to fit the carrier. So I took the carrier apart completely and used it as a sort of "mandrel". All I had to do was to clamp the receiver at the bottom, and then half-insert the carrier, backwards, and use the "nose" of the carrier as a handle to flex the receiver side to side. This is thin, annealed sheet metal, so it does not take much to move it around.



    I will be noting some of the tools I use through the build. I use Kant Twist brand clamps whenever possible. They are great, well worth the investment. The "deep throat" versions around 2 to 2.5" are the best for general gun use, but the smaller 1" versions are really handy.



     
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    jdindadell

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    Time to demil some of the assembled parts.

    Need to free the front trunnion and cocking tube from the original cut receiver section. These are held together with a combination of resistance spot welds and tig welds.


    I find the easist thing to do is to cut the existing receiver along the point where the cocking tube and trunn meet. Being careful to not cut into either, of course!



    At that point I am left with 2 pieces, that are easier to handle and with some receiver edges to get hold of.



    Now I start grinding the visible spot welds on the cocking tube, being careful to not cut all the way through into the parts that I want to save. I will use the now available cut edges to bend the receiver metal away from the parts below, that will often allow me to "pop" the remaining thin receiver sections off around the spot welds. I am careful to not distort the thin-ish metal of the cocking tube when doing this.





    Once the receiver section is removed, I use a combination of dremel grinding disks and a file to clean up the remianing weld section:

    Before:



    After:

     
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    jdindadell

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    A note on files and cutting disks...

    I use a dremel style tool with a flex shaft for most of the smaller cutting and grinding. I have larger air power die grinders with cutting and grinding disks, as well as a bench grinder with 2 different grit wheels. And a variety of other cutting tools which is beyond the scope of this build.

    I find the dremel size stuff best, as they are easy to control, and not very aggressive. This leads to longer work times, but not much, and less chance for error, which is always appreciated!

    I like the quick change dremel attachment, it is very handy. I use the various diameter cutting disks, and the grinding disks are very useful. Not the cheapest, but they are a necessity, at least to me.



    Files, I buy the Nicolson brand from Home depot. I find them to be considerably better and longer lasting that the no-name files, and inexpensive enough to replace when needed. The 8" handi file is a good general purpose file. It has a single cut on one side, a double cut on the other, one edge will cut, while the other edge is smooth. This is important when cleaning up the weld on the top of the cocking tube, as it allows you to remove the weld, without cutting into the cocking tube body. I also have a smaller 6" fine cut file, which is nice for the finish smoothing. I also use sandpaper, 120 and 80 grit, as needed.

    This pic also shows what is called a "file card", which is basically a small wire brush. It allows you to clean the shavings off the file. Larger rough cut, bastard files may not need carding often, but finer cut files do benefit greatly from being cleaned.




     
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    jdindadell

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    Removing the receiver section from the front trunnion is a bit more work.

    There are 4 spot welds on the front sides and bottom. Those can be ground "almost" through. The tig welds on the side are much tougher. I found that it was easier to hold the trunnion in the vise and then use some pliers to "peel" the receiver section away from the welds. This left much smaller sections of weld to grind. My main goal here is not to remove any of the trunnion material at all. I found this best done with the file, as the welds are soft enough to file off, but the trunnion is hardened and the file will not remove metal unless you really push hard. It did take the finish off, but that cannot be helped.






    After some cleanup and smoothing with the small fine cut file:

     

    jdindadell

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    Now we have the main 2 front parts clean and ready to assemble.

    The next step is to see how they fit the receiver shell. In the pic I have it clamped to roughly the correct shape.




    I am testing the magazine fit prior to welding the shell. I have installed the magazine catch temporarily along with the front trunnion and the cocking tube. The cocking tube centers the trunnion, as they can only fit together one way. The trunnion acts as the front mag shelf, and must be positioned correctly (flush with the front of the receiver) in order for the magazine to fit. I had to trim the mag well slightly at the rear to get mags to fit. They are a rock and lock style, like an ak but not as much "rock".

    I have 4 mags that I have test fit in my factory HK 93, then marked them from smallest to largest. The variable dimension is front to back on the mags, they all seem to be the same width. These are factory 40rd aluminum mags. The promag poly mags are another option, but they tend to run slightly smaller than my smallest dimension mag, and slightly narrower. They do wobble a little. So I do not bother to use them for test fit, as they will fit regardless.

    This gun will have a paddle mag release, and I will drill the needed holes a bit later in the build. Also have to make a jig to align those holes, and I will detail that in later posts.

    Note my humorous markings, I get bored sometimes... Tiger tight is the largest mag.



    That is all for now. Next set of posts will cover the barrel install and setting bolt gap, welding the receiver shell, and installing the paddle mag release.

    Any questions just post them up, this will be a longer build as I do not have a ton of time right now to dedicate to this. So far I have about 3 hrs in the build.
     

    jdindadell

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    Subscribed. This is excellent. I would love to build one of these one day. It aint no AR15 build.

    Thank you!

    Yes, it is certainly more time and equipment intensive than assembling an Ar. Not sure where it would fall compared to other builds. Due to the lack of a gas system of any kind there is only really one thing to line up on the barrel, the triple frame. No gas port holes to drill. No rivets to set. 2 cross slots to be drilled in the barrel. And a fair amount of welding.

    I would say it is easier to do than an ak build from a flat... Less tools needed (if you consider that proper rivet tools are needed to build an ak correctly, as I do).

    Mig welding can be done on these, even though Tig is preferred.
     

    2aadvocate19

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    Thank you!

    Yes, it is certainly more time and equipment intensive than assembling an Ar. Not sure where it would fall compared to other builds. Due to the lack of a gas system of any kind there is only really one thing to line up on the barrel, the triple frame. No gas port holes to drill. No rivets to set. 2 cross slots to be drilled in the barrel. And a fair amount of welding.

    I would say it is easier to do than an ak build from a flat... Less tools needed (if you consider that proper rivet tools are needed to build an ak correctly, as I do).

    Mig welding can be done on these, even though Tig is preferred.
    came across this post and really wish it was completed. hope all is well.
     
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