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Thread: MG47 Jr.

  1. #31
    Gunco Member cntrailrider's Avatar
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    Coils -

    I didn't think about it either, until getting into the MG47. The specific reason for installing the left rail first is so the bolt doesn't rotate during cycling tests; and to align it when you slip it in the rear. My ejector rail came with a flat; standard-length factory ejector rail.

    Also, left rail goes in first (and NOT the ejector rail!) so you can 'unchamber' the rds. Otherwise you'd have to cut your ejection port right away. Found that one out the hard way too DUH so now you know I am certainly no expert

    Steve

  2. #32
    No Hope For Me Coils's Avatar
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    so now you know I am certainly no expert
    Your more of one then me on this matter.

    Thanks for the info on the left rail, never would have thought of that.

  3. #33
    Gunco Member cntrailrider's Avatar
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    Cycling without a spring - pull-push wearing a glove. Long strip is the extended cocking plate. Temporary U-shaped recoil spring 'anchor' used to test chambering on this & the MG47 (before FCG & BC ext) is on the lower left


    BACK END of the gas tube is visible, which should yield 5.5" of contained-full-pressure stroke. First pic above shows the piston on short carrier. Ejection port is still undersize. Hammer-to-firing-pin & cocking geometry work very well (quick mock up for pic shows tipped grip, but perm STRAIGHT installation is done)

    The trunnion-to-feed tray & feed-lever-to-stroke 'geometry challenges' are beginning to emerge, since the tray is not on TOP of the trunnion, but behind it. I was afraid to cut the trunnion down to far (up front) so as not to compromise the locking lugs. This results in a longer chambering path, and feed-lever geometry is vastly changed. There are no guarantees on this one, but I'm working on it

    I am open to suggestions which have been thought through. An option may be to extend the widened part of the feed lever (the 'funnel-like' portion, which initially 'kicks it' sideways) so the feed stud can be located further forward. There is space to extend it


    Here's the section of feed-lever I called 'the funnel' for lack of a better term

    When dealing with things like this, one can better-appreciate the engineering mind of SharpShooter, and his level of ingenuity. I am no engineer so it's going to be a steep climb

    Steve

    UPDATE: I have figured out the feed stud CAN be located further forward, to compensate for the longer "dead part" of the stroke which doesn't exist in an RPD. The funnel-like swell at the front of feed lever will 'catch' the stud as it moves aft. So funnel wasn't such a bad term after all. My concern now is whether that 'funnel-bend' will absorb the sudden recoil shock without damage. It seems like an odd set-up to begin with. I believe RPD's have a 'flapper' bolt lock which delays bolt/BC unlocking/velocity, like an HK delayed blowback?
    Last edited by cntrailrider; 03-03-2008 at 04:24 PM.

  4. #34
    Gunco Member SW44's Avatar
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    It may not be any help but I pulled out my RPD parts kit and estimated some measurements. From the front of the FT to the chamber mouth was about 1/4". From the bottom of the FT to the top of the chamber was about 1/8". The edge of the feed lever (start of the "funnel") sits in the middle of the actuator roller when the bolt is closed. Measurements are approximate due to the torch cuts but not too bad.

    The RPD locking mechanism has positive locking and unlocking driven by the gas piston/bolt carrier. The H&K action has an additional delay because the rollers need to be "squeezed" out of the recesses before the action can move back.
    I am not sure that the RPD recoil forces are any worse than the AK.

    I love your work and follow the progress. I would love to see how the cocking plate interfaces with the bolt carrier.

  5. #35
    Gunco Member cntrailrider's Avatar
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    SW44 -

    I Thank You

    The 'cocking plate' is simply a flat plate which lays alongside the upside-down BC, and has a 'catch' on the front, which engages the front 'step' on the BC. It's basically a hook that will pull the BC back, but won't push, so it's non-reciprocating. That's why I'm using a dowel for the front stroke, until I get a butt-plate & recoil spring system made

    There is a rather poor pic of the cocking plate assy belt feed ak-47
    If you look close, you can see the part that catches the BC, right above the body/shank of the bolt. The hole in the plate is for attaching the cocking handle. Right now that's a weak link in the chain

    Steve

  6. #36
    SHARPSSHOOTER5090 SHARPSSHOOTER5090's Avatar
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    Steve
    Here is another thought. If you still can't get the feed stud far enough forward to be at the same distance from the bolt head as on the STD RPK, what if you slotted the bolt carrier holes where you bolt on the 2 pieces of flat bar that goes back and mounts the feed stud angle. Put long thru bolts from one side to the other, going clear through the BC with a nut on the end of each bolt. Put a small coil spring between them with a pin thru the BC back of the spring to press against but ahead of the rear bolt. When the BC goes forward, the feed stud angle would bear against the back of the FT and retract as the BC still goes forward. When the BC move rearward, the feed stud/angle/ flatbars would stay against the back of the FT until the cross bolts came to the end of the slots, at that point the feed stud/angle/flatbar would move back with the BC and into the funnel of the feed came so that the distance from the feed stud to the bolt face would be the same as on the STD RPD. I had to make a similar device on my 300WSM FAL to lock the bolt head from rotating when it stripped a cartridge from the magazine. The trick is to get the spring tension right as it will oppose the closing of the BC spring after the feed stud contacts the back of the FT.

    Just a thought

    Tom Hartman
    SS

  7. #37
    Administrator pirate56's Avatar
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    You can probly save yourself a lot of problems by mounting the feed cover / feed tray in the proper location. I notched my trunnion so the bullet is in the same relative position as a round in a mag in a regular ak. this will allow the bulet guide to work right.
    thats how I did mine and it feeds perfectly.

  8. #38
    Gunco Member cntrailrider's Avatar
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    Pirate - your approach is closest to the original set-up, and you have yours feeding. I need to re-locate the tray forward and re-do the top.

    First, I will try extending the BC ext. longer (forward) and re-locate the feed stud as far front as possible, just to see what happens. It might work. But a more forward-positioned feed tray (where it should have been to begin with, on TOP of the trunnion) WILL keep the feed lever geometry original, and keep OAL of the pistol shorter at the same time. I may still be able to salvage the lower tube. I sure would like to see more pics of yours if you have any

    SS - I followed your train of thought (it would work) but it's rather involved - I need to keep it simple

    Thanks for the shared guidance. All this, after the long-winded "Logic post"......well, humility ain't a bad thing. Experience = list of mistakes, and I have lot's of experience

    Steve

  9. #39
    SHARPSSHOOTER5090 SHARPSSHOOTER5090's Avatar
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    Default Feed Stud

    Steve,
    I agree with Pirate 100%, if you can move the FT forward, it's a much simplier solution. I just thought it was as far forward as you could go. If he has his farther forward and it works, I would try to match his.

    SS

  10. #40
    Administrator pirate56's Avatar
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    Basically I positioned mine so thet the feed tray was in the same spot as an ak mag, that works so this should and it does. I made a sleeve and welded it to a peice of barstock welded to the trunnion. for the feed cover hinge. My concern was that the ak rounds feed from the sides and that there would be a problem feeding from the center but there isn't.

    I haven't installe the rails or ejector yet. I wanted to get the feed cover positioned first. I will be removing the fillers to do the rails now that I know that it feeds.
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