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Thread: Barrel link and timing

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  1. #1

    Barrel link and timing

    Can a loose fitting barrel link at the slide stop pin hole cause incorrect timing during linkdown?

    Lets say a 1911 is setup to link down with the slide at 0.25" aft of battery. When hand cycling the pistol at slow, controlled speeds, the barrel has linked down sufficiently (0.012" to 0.018" clearance from top of barrel above the chamber to bottom of slide lug). In this scenario, the slack from the link pin does not come into play because the slidestop pin "rides" the contour of the barrel's lower lugs.

    However, when the gun is fired, the barrel (initially trying to go forwards) is forced backwards by the slide and the link swings the barrel downwards. In this condition, the slack is taken out of the link by the inertia of the barrel, and the radius the barrel swings down at is larger than it was during the hand cycling. Let's say that the slack is enough to cause this condition to have nearly zero clearance between the top of the barrel and bottom of the slide lug.

    Has the slack in the link caused a mistiming? Thanks for helping out a confused individual.
    Last edited by tophatjones; 8th April 2008 at 22:06.


  2. #2
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    Quote Originally Posted by tophatjones
    Can a loose fitting barrel link at the slide stop pin hole cause incorrect timing during linkdown?

    Lets say a 1911 is setup to link down with the slide at 0.25" aft of battery. When hand cycling the pistol at slow, controlled speeds, the barrel has linked down sufficiently (0.012" to 0.018" clearance from top of barrel above the chamber to bottom of slide lug). In this scenario, the slack from the link pin does not come into play because the slidestop pin "rides" the contour of the barrel's lower lugs.

    However, when the gun is fired, the barrel (initially trying to go forwards) is forced backwards by the slide and the link swings the barrel downwards. In this condition, the slack is taken out of the link by the inertia of the barrel, and the radius the barrel swings down at is larger than it was during the hand cycling. Let's say that the slack is enough to cause this condition to have nearly zero clearance between the top of the barrel and bottom of the slide lug.

    Has the slack in the link caused a mistiming? Thanks for helping out a confused individual.
    tophat, The safe and obvious answer to your opening question is, YES a (too) loose fitting barrel link at the slide stop pin hole can cause incorrect timing at/during link down.

    The proof of this can be had through manual testing. Wil Schuemann has written a very comprehensive article about barrel timing and how to determine it in your pistol. The article can be found on his website, Google Schuemann Barrels and you will find much to read and digest for days.

    1911Tuner has also written much about this very important understanding of the operation of the 1911. You can find some very interesting posts from Tuner and others on the Gunsmithing Sticky Threads at the top of this forum.

    One way, while not as definitive as others, is to hold the gun upside down and cycle the slide, there should not be any sensation of the lugs catching on each other. Also while in this position you can push the barrel back into link down and see the clearance between the top of the barrel and the inside of the slide. Do this by pushing on the muzzle not the slide.

    The correct link should be selected so that when the pin is in the link and held back against the lug feet in the battery position the pin is free to sit on the feet and has minimal clearance at the bottom of the link.

    Read and think about it, it will come to you all at once and you will smile.

    Best Richard

  3. #3
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    Log man defined it pretty well. About all I can add is that the barrel clearance with the slide should correctly exist with all the slack removed from the link by placing it into the test position and forcing the chamber end of the barrel up.

    The test kit uses a spring loaded fixture to accomplish this, but it can be done with a dowel rod or similar tool in the barrel. It's just a bit awkward unless you have an extra hand to assist...or a vise to clamp the frame into.

    You can do a rough field test by holding the gun upside down and checking to see if the clearance obviously changes.
    Last edited by 1911Tuner; 9th April 2008 at 06:54.


  4. #4
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    Quote Originally Posted by tophatjones
    When hand cycling the pistol at slow, controlled speeds, the barrel has linked down sufficiently (0.012" to 0.018" clearance from top of barrel above the chamber to bottom of slide lug). In this scenario, the slack from the link pin does not come into play because the slidestop pin "rides" the contour of the barrel's lower lugs.
    Whether or not this actually occurs depends on the individual pistol.

    In a mid-spec USGI M1911A1 with a standard 278 link, the only time the SS pin contacts the barrel feet is when the gun is in the battery position as shown:

    Other in-spec (but not mid-spec) USGI 1911's may experience some foot/pin contact prior to battery and others may see the feet held farther off the link.

    For a 1911 with a fitted (oversized feet, hood, etc) barrel and perhaps a link other than a 278, this part of your scenario is OK.

    FWIW, doing the Shuemann timing tests is a lot easier if the wood dowel put in the barrel has a small stop about 4" from one end. The stop lets you force the barrel aft and at the same time force the chamber up without pushing on the slide. Putting the forward part of the protruding dowel under the edge of a bench and lifting the gun up while pushing forward against the bench puts the barrel in the position of initial VIS contact after firing.

  5. #5
    intersting??? so i guess it is normal for it to stand on link a bit??? and mid-spec means what exactly??? all tolerances in the middle? of high's and lows and for and afts? it's odd my gun was in mid-spec and i was trying to get it off from standing on the link... so would "in-spec" be a pistol that had link closer to "curvature" as compared to a "mid" spec???

  6. #6
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    Quote Originally Posted by hutch1510
    so i guess it is normal for it to stand on link a bit???
    Yes, based on U.S. Army blueprint data.
    Quote Originally Posted by hutch1510
    and mid-spec means what exactly???
    Mid-spec means each of the dimensions for each of the parts is in the center of the allowable limits for that dimension. If the dimension is 0.278 0.001, the mid-spec value is 0.278. If the dimension is 0.4055 + 0.0040, the mid-spec value is 0.4075.
    Quote Originally Posted by hutch1510
    would "in-spec" be a pistol that had link closer to "curvature" as compared to a "mid" spec???
    Not necessarily.

    An assembly of in-spec parts just means that none of the dimensions on any of the parts is outside the allowable limits. On the same part, some could be above mid-spec but within (or at) the upper limit and some could be below mid-spec but within (or at) the lower limit.

    So an in-spec gun's feet could be closer to or farther away from the SS pin.

    Did I muddy that up enough?

    Cheers

  7. #7
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    Hi

    I suspect you could do something with one of these little super magnets to pull the barrel "up" in the slide.

    Bob

  8. #8
    Join Date
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    Quote Originally Posted by niemi24s
    Putting the forward part of the protruding dowel under the edge of a bench and lifting the gun up while pushing forward against the bench puts the barrel in the position of initial VIS contact after firing.
    Actually, you can check the clearance by simply pressing the muzzle against a table to move the slide until it stops, and verifying that it's a quarter-inch out of battery.
    What we're after here is to determine whether the link has too much slack in it by seeing if the barrel has proper clearance with the slack taken out.

  9. #9
    thanks for the info neimi24 anyway i ordered volume 2 of kerhausson manual or whatever his name is... gonna read it from front to back before i install a kart easy fit to my norinco

  10. #10
    Quote Originally Posted by log man
    The correct link should be selected so that when the pin is in the link and held back against the lug feet in the battery position the pin is free to sit on the feet and has minimal clearance at the bottom of the link.

    Read and think about it, it will come to you all at once and you will smile.

    Best Richard
    Thanks, Richard, I'll try this.

    -Alvin
    Last edited by tophatjones; 9th April 2008 at 18:42.


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