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Thread: in-progress build - question

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  1. #21
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    Forget about needing the 0.020" clearance between the top of the barrel and underside of the slide. A mid-spec M1911A1 has only about 0.006" clearance.

    The initial problem here is that your link is not allowing the barrel to fall all the way down to its bed in the frame simply because it's in compression when you did that test. The simplest cause of this is a link that's too long.

    The standard link is a "278" wihch is the spacing between its hole centers as shown below:

    scan0003atxtc Barrel Link & Pin Dimensions Post 1.jpg
    Q: Does the link you've been using have any marking(s) on to indicate it's really a 278 link?

    If not, you can attempt to measure what should be the 0.097" web between the holes - but that's not an easy thing to measure.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  2. #22
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    Ok, this one will take some doing. I don't see any marks on the part I can see. When Sarco sent the kit, the link was already pinned to the barrel. So far I have not given it the percussive force to remove the pin.

  3. #23
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    If the link pin is tight, place a snug fitting feeler gauge leaf between the link and the inside of the lower lug when you drive out the pin. This is to prevent collapsing the lug sides inward.

    Much of the error in measuring to the edges of the link holes can be compensated out by measuring to the inner edges of the holes, and to the outer edges of the holes, and then averaging the two measurements together.

    So the .097" dimension might erroneously read .098", and the .459" dimension might erroneously read .458", but the average would be a corrected .278".

    The error is due to the caliper jaw edges having a small but non zero thickness. If the inside and outside jaws are of similar thickness, the inside and outside errors will be equal and opposite, and therefore cancel when averaged.

    -
    Last edited by megafiddle; 28th May 2020 at 18:50.


  4. #24
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    As a guess, your link is probably at standard 278 as I don't think Sarco has any other lengths of links. But follow megafiddle's instruction when removing it.

    If the link is indeed a 278 the next suspect is the distance between the slide stop pin hole in the frame and the Vertical Impact Surface (VIS) which is immediately in front of the barrel bed. See if this distance is too short by measuring it as shown below:

    P(12)07220001a Sig Sauer, Frame Defect, Post 20.JPG

    It should be about 0.333" using the slide stop pin or a better fitting drill bit inserted through the holes and pushed aft as a reference surface.

    If that checks OK, put the barrel and bushing back into the slide with the slide upright, the barrel down as far as it will go in the slide and back about ¼" from the battery position. Then use paper shims to see if the distance between the top of the barrel and underside of the slide is any greater than when the slide & barrel were linked together and the gun assembled without the recoil spring. Schuemann specifies this test to see if the slide is keeping the barrel from dropping all the way down onto its bed in the frame.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  5. #25
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    Still can't quite get the link.

    3 measures put that distance just over what you say (0.335, 0.335, 0.336)

    For the second check:
    I'd have to use feelers or shims to measure it, but there is a visibly noticeable difference from when the slide is on the frame. If I hold the barrel there, and try to slide the slide+barrel onto the frame, the barrel contacts the front of the frame rails.

    Thank you for your patience and all for the help you have provided so far.

  6. #26
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    Those three measurements show the frame is within spec for that distance as it works out mathematically to be 0.3325 ± 0.0030. And it's good the distance is toward the long end of the spec.

    That second test with just the barrel & bushing in the slide going on the frame is also good as it indicates the slide is not keeping the barrel from dropping down as far as it should when the barrel is linking down.

    Made a quick review of what you've told us so far and glad I did, as this from your Post #6 finally sunk in:
    When I try to pull the slide back, it moves about 1/4 inch or so, then stops. I have to push down on the barrel (chamber end) to get it to move the rest of the way.
    That's an indication that the barrel bushing is interfering with the free movement of the barrel as the chamber end drops back down to the horizontal as the gun comes out of battery.

    Carefully examine the barrel and bushing to see if there are any telltale wear patterns in their finishes showing contact that would cause the bushing to lever up the back end of the barrel.

    Also check to see if the front flange of the bushing is parallel to the front of the slide when they're put together.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  7. #27
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    Quote Originally Posted by niemi24s View Post
    Those three measurements show the frame is within spec for that distance as it works out mathematically to be 0.3325 ± 0.0030. And it's good the distance is toward the long end of the spec.

    That second test with just the barrel & bushing in the slide going on the frame is also good as it indicates the slide is not keeping the barrel from dropping down as far as it should when the barrel is linking down.

    Made a quick review of what you've told us so far and glad I did, as this from your Post #6 finally sunk in:That's an indication that the barrel bushing is interfering with the free movement of the barrel as the chamber end drops back down to the horizontal as the gun comes out of battery.
    Minimal wear patterns near the front of the barrel that I can see. Only thing I see on bushing is tiny wear at front bottom. Bushing is flush with the front of the slide, no apparent gaps between mating surfaces.

    I might be missing something, because some of this seems to be conflicting. With the slide on the frame, the vertical travel of the barrel appears to be constrained more by the frame rails and the bed than the bushing. Without the slide stop pin holding the link, the barrel drops when I move the chamber end forward of the rails. If it were the bushing causing that interference, I would expect it to continue after moving forward of the rails, and the barrel would not drop at that point?
    Last edited by joral; 29th May 2020 at 10:30. Reason: correcting wear observation


  8. #28
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    The logic of your second paragraph sounds good, but there's just got to be something keeping the barrel from unlocking from the slide when coming out of battery - at least until you push down on the chamber. Hmm-m-m---

    Put that pin or drill back through the slide stop pin holes, lift up on it and measure the distance from the top of the frame rails down to the top of the pin/drill. It should be about 0.347 ± 0.003 inch.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  9. #29
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    That may be it. 0.355, 0.356, 0.354 (so about +.008 from your spec)

    A part of me keeps wandering back to that 9mm / 38s question. For other barrels, are the outer dimensions still the same? I can't find anything that says they're different, just the feed ramp. Just can't help but wonder though.

  10. #30
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    Even though an average of 0.355" is a bit out of spec, being a little too far down is OK in the sense that too far up is the way that would keep the barrel from unlocking. But in your photo in Post #15 I see a bright rub line in the bottom of the link clearance cut below the slide stop pin holes. If the link is rubbing there because the slide stop pin hole is too low, maybe that could be the culprit. Maybe.

    Does the outside surface of the links lower end show a matching rub mark?

    The minimum distance from the bottom of the slide stop pin holes down to the bottom of the link clearance cut is 0.103" (#38 drill bit) - what's yours measure?

    Also, the minimum distance from the tops of the frame rails down to the bottom of the link clearance cut is 0.654".

    In any even and even with tolerance stacking, the link should never contact its clearance cuts in the frame or barrel, as shown below:

    P(09)3060001b Recoil Spring Replacement, Post 40.jpg
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Last edited by niemi24s; 29th May 2020 at 15:30.


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