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Thread: PKM Parts Layout

  1. #21
    Master Endmill Breaker Rhino_66's Avatar
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    I'm interested to see what you guys are going to do for the striker/hammer for this thing. It's a beautiful weapon, but there's not much room left in there...


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  2. #22
    Happy Camper hcpookie's Avatar
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    Yeah well if you can find where to get stuff like the carry strap, drop case, and all those tool things I'd like to know too!

    I wonder if the 200-rounder box lids can be cut & re-welded to 100 round size? I read the boxes are aluminum so maybe not...
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  3. #23
    Happy Camper hcpookie's Avatar
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    Quote Originally Posted by Rhino_66
    I'm interested to see what you guys are going to do for the striker/hammer for this thing. It's a beautiful weapon, but there's not much room left in there...


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    I'm thinking some milling will need to be done to remove material around the sear. I think either the hammer can be connected above the bolt carrier and swing down to hit the firing pin, and the sear (disconnector) would be mounted somewhere directly behind the bolt. Assuming that there is enough room to clear the bullet extractor claw that removes the bullets from the belt on the backward motion.

    That would make the need for a trigger that had a long L-shaped bar attached so that it would reach up beside the carrier and touch the sear. Another option would be to make a VZ-58 style of mechanism that is striker-fired. You'd need a long trigger arm no matter what.

    I don't see any reason that would couldn't make the receiver 1/2" longer to make room for the parts.

    I think there will be some work involved to shim or block the receiver Uzi-style so you can't insert the original bolt carrier into the receiver. That means milling a notch into the carrier like on the Uzi or like the 1919a4 semi that lets only the semi carrier fit.

    It will be a challenge to be sure! I was surfing Weaponeer's ATF letters forum and found that is kinda what the M60 semi conversion did/does:

    http://www.weaponeer.net/forum/forum...?TID=1110&PN=1
    Last edited by hcpookie; 02-08-2006 at 08:16 PM.
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  4. #24
    Happy Camper hcpookie's Avatar
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    A few more design ideas. Thinking about the blocking shim that prevents insertion of a FA bolt carrier, there is some room on the left side of the bolt carrier that would be suited for this. In this pic, the area I'm suggesting is directly below the "194" at about the 6" mark on the tape measure:

    http://pookieweb.dyndns.org:61129/be...M/DSCN1746.JPG

    The area would need to be matched to the extended part immediately to the left of the tape measure. That would allow us to put a blocking shim on the left hand bottom of the receiver and it would be about 1/4" high. I think it wouldn't have to be any more than about an inch or two long, and it could serve as a lower guide rail if it were long enough to support both of these extended segments.


    The sear engagement notch could also be ground off, since it would be moot. However, the bottom of the bolt carrier is worn smooth, suggesting the carrier touches either the bottom of the receiver, or more likely, a spacer to keep it off of the rivet heads for the trigger frame.

    http://pookieweb.dyndns.org:61129/be...M/DSCN1747.JPG

    http://pookieweb.dyndns.org:61129/be...M/DSCN1748.JPG


    I don't think the trigger frame could be moved backward or forward. The trigger has a lug on the front that engages a mating tab on the tripod. Therefore the trigger group should stay in the original location. The good thing for us, is that the tripod mounting arrangement will help to confirm that the trigger frame is at the proper position!

    Here, you can see where the measurement I'm getting is 5 11/16" from the rear of the receiver to the front of the mounting lug (the tape measure is set to 10" at the rear. That is as far forward as it can go and still be mounted on the tripod. The locking tab on the tripod would allow it to be moved back 1/16" with no problems. At about 1/8" it may no longer engage unless the tab on the tripod is modified.

    http://pookieweb.dyndns.org:61129/be...M/DSCN1749.JPG

    http://pookieweb.dyndns.org:61129/be...M/DSCN1753.JPG

    http://pookieweb.dyndns.org:61129/be...M/DSCN1754.JPG
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  5. #25
    Master Endmill Breaker Rhino_66's Avatar
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    This would be a perfect case to get a letter from the ATF for classification. The MG42 was determined to be a "firearm", not a rifle. It is shoulder supported, not shoulder fired. As such, it is not a semi-automatic rifle and is therefore not subject to 478.39 for parts count.

    Since there is no forearm to support the front of the PKM, it would most likely be classified as a "firearm" instead of a rifle.

    The sear notch could be milled with a bevel to eliminate any possibility of it catching on the sear.

    With the rear block being riveted, that kinda limits what you can do. If it were removable (like an HK buttstock), you might be able to come up with a striker to ride in a set of rails. There would still be a problem with needing a guide rod to keep the spring retained.

    If the guide rod is attached to the striker instead of the rear block, it could be pushed back through the block and into a hole in the stock (think of the rattail on a FAL carrier).

    For a sear, you could mill a latch mechanism to attach behind the buffer plate. If the sear lays horizontal, a vertical arm could pull it down on the back end of the sear to pivot it off of the striker. To connect the vertical arm to the trigger would require a horizontal arm. By adding a hump to the horizontal arm, you would effectively have a disconnector (like a Sten trigger bar). Does that sound convoluted enough?

    I wish these kits weren't so expensive. I think it's a really beautiful weapon, but I can't float the coin for one.
    The most damning evidence is the truth.

    That which does not kill you, really really really hurts...



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  6. #26
    Happy Camper hcpookie's Avatar
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    Yep, I had considered the same thing after looking at my VZ kit. I measured the buttstock earlier and you have a good 4" of useable buttstock behind the rear stock tang. There is just about 5 1/16" in-between the rear of the bolt ( in battery) and the back of the receiver. Not sure if that would work.

    Assuming it won't, I'm thinking about something that imitates the general action of a semi AK, but along a different geometry. I'm going to make a pic to explain, it is too involved to try to type out...
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  7. #27
    Happy Camper hcpookie's Avatar
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    OK Here's the pic:



    Now, what I tried to do is capture the idea. Basically, the hammer gets mounted on the side of the receiver, and is hinged at the front. It rotates forward into the firing pin and is pushed backward against the disconnector & trigger by the RH side of the bolt carrier. The trigger axis pin is vertically aligned, not horizontally as with the AK.

    The disconnector would just catch the end of the hammer, similar to the way the AK disconnector works.

    The trigger shape I'm thinking is like an AK trigger single-hook but with the hook 1.5" farther to the right. The hook is offset to the right, and backwards about 2" or whatever it takes to reach the "working" end of the hammer.

    The disconnector/trigger relation is almost the same as with an AK, however the disconnector is on the RH side in the same plane as the tip of the trigger.

    Does that make sense? It is kinda like a Maxim animation I saw on the History Channel once.

    If my abilities to think in 3D were better, I would make the bottom end of the trigger notched in such a way as to require a less-complicated trigger design. I think the design could be improved upon, but there you have it.
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    The "original" Boltcutter Rivet Squeezers:
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  8. #28
    Master Endmill Breaker Rhino_66's Avatar
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    Okay, here's what I drew up at lunch time today...




    The striker is basically a block with a threaded hole. The guide rod screws into the striker and is brazed or pinned. The striker has a ridge on each side to fit into rails inside the receiver. The rails align it with the bolt.

    The trigger is attached to a draw bar. The draw bar has a raised area to act as a disconnector. When the carrier travels back, it pushes the draw bar down and disengages it from the rest of the mechanism. The mechanism will then reset the sear and catch the striker.

    The vertical and horizontal bars of the mechanism are connected by a cam. When the horizontal bar is pulled forward, the cam will rotate and pull down on the vertical bar. The vertical bar will pull down the back of the sear and release the striker.

    The drawing in the bottom right shows the fixed pivot points in blue. The direction of travel of each piece is shown by the arrows.

    Not shown are the springs to reset the sear or the draw bar.

    If a setup like this is used, a new trigger housing would be a good idea. The housing could have sides that extend up into the receiver. The rails for the striker could be milled into the side plates of the housing.

    The carrier would need to be milled to clear the rails and side plates of the housing, but this would ensure that an unmodified carrier could not be used. It would also prevent installation of an original trigger housing/grip assembly.

    Since you will be making your own receiver, you could make it a little longer than original. This would allow room for the striker and sear assembly.

    What do you think?


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    That which does not kill you, really really really hurts...



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  9. #29
    Happy Camper hcpookie's Avatar
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    Rhino, I'm feeling it. I believe I understand your design and it looks sound. Like a big VZ-58. I wonder how much leverage would be needed for it to not require a great deal of pressure on the trigger?

    There isn't that much room on the bottom, and I think that trigger bar would have to be located on the side of the receiver to happen. OR be a more complex piece that reaches back and to the side.

    That it needs to go outside of the stock is a concern, and the more I look at the stock tang, the more I think it won't be a good idea to cut that area down. The center part of the stock tang actually sits inside the receiver in such a way that if you remove the buttstock, the stock tang creates a recessed cavity. This is also what the hammer bangs against, just like an AK. I don't know if removing this metal would weaken the receiver or interfere with the inertia of the recoil spring? Not sure on this.

    Let's assume that we could do the striker without harming the tang, or remove enough from the tang that it doesn't matter... the pivot block at the bottom would need how much room I wonder? A notch could probably be cut from the bottom of the carrier to let it ride in the bottom rear of the receiver. THere's also enough space between the bolt and the recoil spring that I think you could cut a horizontal section from that in-between section and have it work, but that would affect the geometry of your design.

    I bent some sheet metal into the proper size and C-Clamped the trunion and stock tang, and there is more room on the sides than I thought there was. I'll put some pics up later.
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    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
    http://pookieweb.net/pink/pink.htm

  10. #30
    Master Endmill Breaker Rhino_66's Avatar
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    I was thinking that you could make the receiver a little longer than necessary. You could rivet the stock tang in place, but the extra length would allow you to slide the sear mechanism in from underneath.

    In all honesty, I would seriously consider making a new grip housing. That way you could be sure to machine it exactly as needed.

    Using a fulcrum like that in my drawing, you could adjust the lengths of the arms and position of the pivot pins to minimize travel of certain pieces and maximize the travel of others. A 1/8" movement of the fulcrum could translate into 1/4" movement of the sear.

    If there is enough room on the sides, your side swinging hammer should work. It will be interesting to see how much room there is between the receiver walls and carrier.

    I would love to actually get my hands on one of these kits, but my funds are being directed to other projects. I do have another project in mind, so I will be watching to see what you and pirate come up with.


    .
    The most damning evidence is the truth.

    That which does not kill you, really really really hurts...



    Gunco Member #21

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