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Thread: Stopping Barrel Fall At Linkdown

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  1. #1
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    Stopping Barrel Fall At Linkdown

    Much is written about what should arrest the barrel's downward movement at linkdown. Some say the VIS in conjunction with the link in compression with no contact with the receiver bed. Others say by the receiver bed alone with no compressive force on the link.

    Based on Ordnance Dept. blueprint spec's it seems a vast majority of GI M1911A1's assembled with in-tolerance parts would have the barrel stopped by receiver bed contact.

    This conclusion was based on determining what "size" link would be needed to halt the barrel's downward motion by contact with both the bed and the VIS, with the link just starting to get compressed. A slightly longer link would prevent barrel/bed contact and thus stop the barrel by link compression/VIS contact. A slightly shorter link could never be in compression and thus rely on bed contact to do the stopping.

    Note: "Size", as used here, refers to the distance between the edges of the link holes [ O<size>O ] - not their centers.

    The only assumptions made were: barrel bore axis was parallel to the receiver top at linkdown; barrel link pin diameter equalled the feet hole diameters for a press fit.

    Calculations (lots of 'em!) led to 0.1056 +/- 0.0102 inch as the "size" needed to stop barrel downward movement by both the VIS and the bed. With no specification available for the link, a new, unused Colt standard "0.278" link was measured and its "size" was 0.097 inch. In a mid-spec GI M1911A1, this link is almost 0.009 inch short of allowing stoppage by both the VIS and bed, could therefore never be in compression, and would thus cause the barrel's fall to be halted by the bed.

    Don't know what JMB's intention was for this, but it seems (to me at least) that most GI M1911A1's assembled with in-spec barrels, barrel link pins, links, slide stop pins and receivers would stop the fall of their barrels by contact with the receiver bed - and their links would be loose at linkdown.

    If all this is close to being correct, why all the fuss about avoiding barrel/bed contact? Was JMB wrong? Or, does it really make any difference how the barrel's fall is stopped?

  2. #2
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    Quote Originally Posted by niemi24s
    If all this is close to being correct, why all the fuss about avoiding barrel/bed contact? Was JMB wrong? Or, does it really make any difference how the barrel's fall is stopped?
    No. JMB wasn't wrong. The barrel should be stopped a thousandth or two off the bed, but most pistols born after about 1937 do stop on the bed. The trick is not to let them hit the bed first, before the barrel's rearward movement has been stopped by the VIS. Once the barrel has stopped, it can freefall onto the bed without problems.
    It's when it hits the bed while still moving that bad things happen.

  3. #3
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    I appreciate both of these posts. I had wondered how that worked but didn't really know enough to even ask the question......now, one has asked and another has so excellently answered. Thank you!
    Lynnie, "Nobody realizes that some people expend tremendous energy merely to be normal. "
    - Albert Camus

  4. #4
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    Others say by the receiver bed alone with no compressive force on the link.
    Niemi, could you be more specific about just who has said this??

    Second thought: You say that link selection is done to determine how to properly halt the barrel in linkdown. I don't believe this is completely correct. While link length does affect how the barrel stops, the link length (these days) is selected based on the position of the lower lugs when the barrel is fully in battery. Given a particular gun with its own unique vertical stacking dimensions, you will select a link that allows the slide stop to support the lower barrel lugs in battery.


    -Lazarus
    "Do not fix that which is not broken."

  5. #5
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    The receiver bed? Think I've seen that in one of Kuhnhausen's manuals.
    xxxxxx Iron bottom sez; Don't let your Rat Terrier hang around with college boys.

  6. #6
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    Hi Lazarus: The answer to your question;

    Ken Hallock, on page 126 of his book, Hallock's .45 Auto Handbook. In his description of how to check if the link is too long he says the barrel should seat firmly into the curvature in front of the feed ramp (bed) when pushed down and back, and the slide stop should not be under any pressure from the link and be free to move.

    Regarding your "second thought", I agree with you completely. My apologies if I implied I was going to use any of my findings to select a link to allow a certain linkdown condition. My aim was simply to determine how a mid-spec GI M1911 halted the fall of its barrel, and the link's hole edge separation was the simplest way I could find to make that determination.

  7. #7
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    re:

    Hallock...

  8. #8
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    Ok, then

    Suprising what you can find these days. Kind of like that guy who thinks his recoil spring somehow affects the trigger pull. I have a copy of book, currently sold by Brownells and others, who advocates the removal the extractor's middle "hump". He states that it is only there to make it easier for production line guns to get a working extractor. The "real" method involves removing it and using his special adjustment technique. Fortunately, this suggestion is not widely distributed on the 1911 forums.

    -Lazarus
    "Do not fix that which is not broken."

  9. #9
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    Quote Originally Posted by Lazarus
    Suprising what you can find these days. Kind of like that guy who thinks his recoil spring somehow affects the trigger pull. I have a copy of book, currently sold by Brownells and others, who advocates the removal the extractor's middle "hump". He states that it is only there to make it easier for production line guns to get a working extractor. The "real" method involves removing it and using his special adjustment technique. Fortunately, this suggestion is not widely distributed on the 1911 forums.

    -Lazarus
    LOL. And I once read, in a shooting magazine, that a lighter weight pistol would permit the shooter to feel less recoil since, if I recall his goofy logic, there was less mass to hit your hand. I kid you not.

  10. #10
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    Hump

    Laz...While I don't remove the outboard dogknot, I reduce its size by about .015 inch on most installations. It lets me put a little more bend in the stem without making the extractor so stiff and unyielding on the front half...and it gives the extractor a little more wiggle room when the channel gets all canked up...AND...it allows the hook to snap over the rim easier in case the round happens to push-feed. I guess I've added yet another redundancy to the system.

    Works well, but usually requires a fitted firing pin stop to keep it from clocking.

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