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  1. #1
    Join Date
    Dec 1969
    Posts
    8,308

    Default FBP bolt in MP40, problems

    I find that the ledge in the FBP bolt I bought is a less steep angle and shorter than my original MP40 bolts. Thus, the FBP bolt I got from IMA will engage the sear manually, but not after a rebound or two during operation, causing it to "run" for maybe 10 rds, sometimes the full mag. Anyone tried to modify an FBP bolt? What about removing material on the sear ledge that stops the sear from protruding into the tube? That is, the sear ledge that is stopped by the receiver tray such that the sear does not rise up any farther into the tube? I probably have only a bit to go, don't want to alter any original parts. What about milling down the flat in front of the FBP bolt ledge?
    Regards,
    HB

  2. #2
    Join Date
    Dec 1969
    Location
    Indiana
    Posts
    149

    Default

    Had a full mag run away on my MP41, got a new (MP40) spring ... but have not tried again.

  3. #3
    Join Date
    Dec 1969
    Posts
    8,308

    Default

    Tried changing springs to Wolff, cutting a bit off the FBP original, etc. Good call but I don't think that's it, but that was my idea for a long enough time to cause me to go through all the iterations of spring changing. I noticed when I rapidly manipulated the bolt by hand, racking it back and releasing it, hard, but of course less than what firing would do, it would fail to catch on the sear. The German bolt caught every time. The German bolt doesn't run away, accept on low powered Denel / PMP which goes putt putt putt about 5-10 times until one with enough oompf pushes the bolt back far enough.
    Last edited by Hambone; 03-24-2008 at 12:25 AM.

  4. #4
    Join Date
    Dec 1969
    Location
    Texas
    Posts
    5,395

    Post

    I have one of those FBP bolts but I have yet to try it out on my MP-40. I appreciate the forwarning.
    What has our country become? More takers than givers.

  5. #5
    Join Date
    Dec 1969
    Posts
    8,308

    Default

    Ricky, if you assemble the FBP bolt, rack it back fast and hard and release it without touching the trigger. If it overrides the sear at all, even a couple times, it is going to run away on you.

  6. #6
    Join Date
    Dec 1969
    Posts
    47

    Default Have FPB bolt runs in my MP40

    I have a very beat up transferable MP40 (original WW2 steyr manufacture) and the belgian FPB bolt runs great in my gun. Guys who have tube guns (US made receivers) have problems with these bolts sometimes.

    Brian Stewart

  7. #7
    Join Date
    Dec 1969
    Posts
    8,308

    Default

    Mine are not tube guns Brian. Originals. You can compare the bolts side by side and see a noticeable difference in the angle and height of that sear catch in the bolt. Being an open bolt weapon I want as much sear/bolt interface as possible. Drop that puppy and putt putt putt putt it goes bouncing about. Bad juju. I think the remedy may be modifying another sear by grinding/polishing a bit on the underside where it contacts the receiver tray such that more sear protrudes into the tube.

    I wish my FBP bolt would work. I like that fixed pin and it looks well made.

  8. #8

    Default

    For what it's worth, Ham, when I first got my MP40, the WWII German bolt skipped off the sear 75% of the time when cycled by hand. I never live fired it under those conditions and sent it to Ohio Ordnance for repair. They replaced the sear block as well as the trigger return spring (which I believe to have been the main culprit). It now runs like a top. It's worth looking into anyway.

    For the record, my MP40 is a WWII parts kit on a wilson tube and an FBP bolt was just a weeee bit too wide to slide reliably in the tube. It would cycle for a few rounds then jam up so I sold it to another guy and bought another German bolt and recoil system.
    REMOVED

  9. #9
    Join Date
    Dec 1969
    Posts
    8,308

    Default

    Thanks Chuck. I'm going to experiment a bit more. You may have a good point there with the return spring! I may get the spare sear I have, take a little off the stop and see if I can get a replacement return spring. Good info and thanks again!
    HB

  10. #10
    Join Date
    Dec 1969
    Location
    Siloam Springs, AR
    Posts
    135

    Default

    I tried an FPB bolt in both my C&R MP40s and experienced similar problems. If someone comes up with a practical fix, I'd be interested.

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