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Thread: MG47 Jr.

  1. #151
    Gunco Member dvanncvann's Avatar
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    I gotta build me 1 of those!!!!!!!

  2. #152
    Gunco Member cntrailrider's Avatar
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    Today was testfire #2 and it didn't go very well. I tapped a screw thru the gas block, to limit pressure, and started with it fully shut. It still cycled, real strong. But soon the cocking plate began hanging up on the cocking tube, when manually cocking. That was the first clue, but I didn't pick up on it. Then I noticed when cocking, it wasn't as smooth, and the rear of the stock seemed to be shifting left. Finally the BC stuck in the aft position, and where the stock joins the rcvr, a gap was opening up on the right side.

    It beat the recoil spring gude tube (which is on the right side) against the back-plate, where the stock is attached. Very minor damage (more like evidence) and the rcvr and pin holes are intact. One M11 spring is not strong enough to counter the recoil. There is enough space to locate another recoil spring set-up on the left side, then go from there. Also thinking about a stiff coil-spring buffer behind the bolt stem. There's very little rear surface area for a buffer

    I am wondering if a rotating bolt and a super-tight gas system would have been better than straight blowback. I didn't think x25 would have this much energy, while cycling the belt feed mech

    On a brighter note, accuracy was good. Was hitting milk jugs @ 150 yards, even though I was distracted with the other problems. I only shot about 30 rds

    Steve

  3. #153
    aka: SDK1968 dutigaf's Avatar
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    stay after it bub.

    yes the x25 really does make this kind of power and if you stumble across some hot stuff its WAY more than that.

    even if you just ad a small piece of leather in the back as a buffer (like the pps43) it will help you a bunch.

    same thing on evening out your spring vs bolt ratio... im gonna go back and re read this thread and see if you got your bolt weight listed. cause if your bolt is about the same weight as ppsh 41 bolts and your in a blowback set up, then your spring from one of those would be perfect.

    or if you are down at the pps 43 bolt weight then one of those springs which is a bit longer would be the trade...

    the gas tube set up would be cool, but this cartridge has been used in about 40 million firearms in blowback set ups ... so im sure you will get it with ust a little more tinkering.

    its a fun to watch build.
    say what you mean & mean what you say


  4. #154
    Gunco Member cntrailrider's Avatar
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    Sorry double post
    Last edited by cntrailrider; 07-20-2008 at 04:05 PM.

  5. #155
    Gunco Member cntrailrider's Avatar
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    Dutigaf -

    Thanks for the support. I'm not abandoning the project at this point -

    Here's a pic of what happened. Fortunately the damage is only to the stock insert where the tube is welded to the rear; the back of it pounded against the backplate, bending the right side out. It can be bent/pressed back into shape. Front of the tube is slightly mushed. From the top, looking down:



    B & BC weigh 15.6 oz - intent was to keep the weight down, plus be internally self-contained

    Here are the BC's from previous builds, with a long "L" type extension:

    #1 = 22.8 oz
    #2 = 21.4 oz (Jr, using RPD cover)
    Standard BC + bolt weigh 17.3 oz

    I could insert round stock inside the (unused) BC recoil spring cavity to increase the weight. A better choice would be adding a recoil spring on the left side
    ************
    Just now snapped this pic to illustrate another possible solution. Small section of spring is just for display/clarity


    The feed stud PLATE could be replaced with a section of square tubing, sliced edgeways, into an upside-down "U" cross-section, 2.5" long (image is distorted / tube is 2 & 5/8" till impact) The back end of it would be closed flat, creating a rear buffer surface between it and the stock insert. Buffer cut to the insert profile, and slipped on over the tube. This would add some weight to the BC, and limit the rearward travel, with an evenly distributed impact, instead of being on one side. Thinking this out as I type. I have some of the liveliest conversations in the shop, when I'm alone.....

    Steve

  6. #156
    No Hope For Me Coils's Avatar
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    The feed stud PLATE could be replaced with a section of square tubing, sliced edgeways, into an upside-down "U" cross-section,
    Very good idea
    The back end of it would be closed flat, creating a rear buffer surface between it and the stock insert.
    The only thing I'd worry about with this is interfering with the hammer swing.

  7. #157
    Gunco Member cntrailrider's Avatar
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    Coils -

    Hammer swing will clear it

    The difficult part is getting the feed stud location in the exact same position again, for smooth feeding. Plus a reinforcement plate on top for deeper stud threads

    Steve

  8. #158
    Gunco Member cntrailrider's Avatar
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    Another error / duplicate post

    If someone would tell me how to delete a post I'd appreciate it

  9. #159
    Administrator pirate56's Avatar
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    use a buffer to stop the bolt, this round is to hot to use just a spring.

  10. #160
    Gunco Member cntrailrider's Avatar
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    Just completed the left side of a twin-spring system. Much stronger stroke. Also a telescopic spring loaded buffer, with a recessed plunger that centers on the back of the bolt. Very heavy short spring, located directly in front of the top TD pin. It's ready to shoot, pics later

    Steve

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