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1911 Clinic. The barrel link

Discussion in 'Gunsmithing and Repairs' started by bigjim, Dec 27, 2003.

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  1. bigjim

    bigjim Member

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    What is the barrel link? What does it really Do? How do you know your barrel link is the right size?

    What is the correct name for the ramped projection that the barrel link rides in with the pin through it to hold it in place? What is the purpose of this "barrel foot" besides holding the link to the barrel?


    See attchment for a picture[​IMG]
     

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  2. BigG

    BigG Member

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    That's the bbl lug. The profile of the lug follows the slide stop pin to unlock and lock the bbl. According to 1911Tuner, the link just keeps everything in place and does not do much for bbl lockup or unlocking. The lug needs to be accurately machined for the pistol to work right. I know Jerry Kuhnhausen's book stresses cutting the lug accurately. HTH
     
  3. 1911Tuner

    1911Tuner Moderator Emeritus

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    Link

    Ah! The oft-misunderstood link. Due to some misconceptions
    about that simple little machine, I'll watch this one for a while
    to get some input.

    One thing that I will say is that the link is NOT supposed to
    put the barrel into vertical lock, though many ill-informed
    tinkerers install a longer link in hopes of enhancing accuracy
    with a better vertical lockup. While a long link will often remove
    vertical barrel play, it won't help the accuracy,and as often as not,
    will actually make it worse. In fact, when the barrel is in vertical lock and the slide in battery, the link should be under no load at all. If the link
    bears the load of vertical lockup, the condition can do damage if allowed
    to remain for very long. Depending on how MUCH of a load that it bears,
    and how long it delays barrel linkdown, the damage can be done in as little as 100 rounds.

    Now that there's a mad scramble to remove all those long links, I can
    sleep better tonight.:D

    Nitey-nite!

    Tuner
     
  4. Delmar

    Delmar Member

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    How do you check the lock up to make sure the lugs are bearing on the cross pin when in battery?
     
  5. 1911Tuner

    1911Tuner Moderator Emeritus

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    Lock-up

    Delmar asked:

    How do you check the lock up to make sure the lugs are bearing on the cross pin when in battery?

    Color the lug with a blue, chisel-point felt tip marker...Marks-a-lot is a good one. Look for even rub marks just at the point that the pin starts to go around the corner all the way to lockup. Note that if there is vertical play in the barrel, you'll get a false reading. If the rub marks start after the pin has engaged the bottom of the lug, the barrel is riding the link a little.


    Tuner
     
  6. Jim K

    Jim K Member

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    The link plays (or should play) no real role in barrel lockup. This can be tried simply enough by removing the link and working the gun without ammo. The cam surface of the "foot" rides up on the slide stop to lock the barrel. If the barrel "rides" the link during lockup, the narrow center contact allows the barrel to be "wobbly" and accuracy suffers. That is why folks recommend that the barrel "feet" be even and bear evenly on the slide stop, rather than the link bearing on the slide stop.

    But the link IS needed for positive unlocking. Again, easy to try at the same time. Remember, in recoil, the barrel-slide unit will remain locked until an outside force (outside the barrel-slide unit, that is) unlocks them; that force is the link, which is fixed at one end and allows a circular motion at the other, drawing the barrel out of engagement with the slide.

    Barrel movement begins at the same time the bullet begins to move, but the greater weight of the barrel-slide unit keeps the unit locked until the bullet exits the barrel. Yes, this means that the barrel is actually moving while the bullet is still in it, another reason to ensure the barrel-slide stop contact is correct. Kuhnhausen, very good in other ways, says some "thrust vector" keeps the barrel from moving until the bullet exits; he is wrong, and his "thrust vector" is nonsense.

    Jim
     
  7. 1911Tuner

    1911Tuner Moderator Emeritus

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    Ladies and Gentlemen...

    Welcome Jim Keenan into the fray. Jim is a savvy old pistolsmith up in
    Maryland, U.S.A. He knows his stuff, but he ain't in the habit of chewin' his
    cabbage twice when somebody wants to fight over a fact. He's also a helluva nice guy that will take the time to explain something,and has experience with many gun designs and models aside from the 1911.

    This is gonna prove to be a good workshop. Let the discussions and
    debates begin!

    Tuner
     
  8. bigjim

    bigjim Member

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    OK fellas,

    I hear what your saying about the link pretty much just acting as a lever to pull the barrel out of battery but.....


    How does this jive with the existence of the Wilson group gripper guide rod that uses a spring loaded link to force the barrel up?

    Inquiring minds want to know!
     
  9. bigjim

    bigjim Member

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    Thanks Jim,

    That helped me a good bit. So is it safe to say if anyone ever recomends long linking a 1911 to make it more Accurate they are full of crap?
     
  10. Delmar

    Delmar Member

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    I must be missing something here-if the barrel begins to move backwards at the same time the bullet is headed towards the muzzle, then why is lockup at the barrel lug so important? Is the barrel NOT floating somewhere between full lock and rearward movement?

    Just swagging here, but I would think the bullet, being of much less weight would begin moving first because of its lighter weight? BTW, I don't buy into Kuhnhausen's theory of the bullet out of the barrel before unlocking begins-the pressure would be gone when the bullet exits the muzzle, and in order to have inertia, you have to have movement and weight.
     
  11. romulus

    romulus Member

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    What is the barrel link? What does it really Do? How do you know your barrel link is the right size?

    What is the correct name for the ramped projection that the barrel link rides in with the pin through it to hold it in place? What is the purpose of this "barrel foot" besides holding the link to the barrel?


    I think that projection is called the "barrel bed" or the "frame bed". The barrel foot is supposed to mate with the slide stop pin for maximimum lock-up (no discernable play). As to right size, I hope to find out by sticking with your lesson plan.

    Thanks
     
  12. BigG

    BigG Member

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    Delmar, I think I know what you are asking, so here goes. What you are thinking about is the timing of the unlocking.

    If you look at the picture of the lug, you'll notice two small projections at the rear. Those are known as the barrel feet. The slide lock pin is up against those feet when the gun is in battery. It is also riding on the flat portion of the lug. You'll notice that the curve of the lug is not a nice circular profile but flat before it starts to curve. This is a guess, but I think the barrel moves STRAIGHT back about maybe 1/16" before it starts to go down to unlock. That's the dwell time that the bullet has to leave the bbl. The old master balanced the two forces, i.e., the bullet and the slide masses and figured that that distance was enough to allow the bullet to leave the bbl and release the pressure. They are both moving at the same time, but the heavier mass moves so much slower. What you are maybe not taking into account is that the process of firing the cartridge has hit the slide with the same force as the bullet. The lesser mass moves first, but the slide has also received a helluva kick. So the inertia of that kick completes the action of cocking and the spring returns the slide to battery.

    What I'm saying is, the bbl is fully locked during that 1/16" or so that it travels to the rear before the slide stop pin hits the curve of the lug. So it is fully supported (not floating) while the bullet is in the bbl and would have no effect on accuracy if properly fitted. HTH
     
  13. Delmar

    Delmar Member

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    Thanks, Big G. I had an idea this might be the case, but it always helps to hear it explained, too. I've been fooling around with the 1911 for over 30 years, and understand alot, but always willing to listen and learn. This forum would never be the great place it is without the people we are blessed to have here.
     
  14. bigjim

    bigjim Member

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    Thanks guys this is exactly the kind of tone and exchange of information I was hoping for.

    I hope some Anti-gunners are watching.
     
  15. Jim K

    Jim K Member

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    Delmar is correct, though it is a bit more than 1/16". The distance is critical and can affect extraction and other areas.

    There are plenty of high speed movies showing (when projected in slow motion) the barrel moving backward before bullet exit. The force involved is recoil, which is why the gun is called (surprise!) a recoil operated pistol. Some folks just can't accept recoil since it is something that sort of has to be taken on faith, so they come up with the drag of the bullet in the barrel, or the pressure on the slide, and other ideas. A blowback action is more easily understood because we can grasp the idea of pressure moving the slide. But the 1911 and all similar pistols (even ones as unlike as the Luger and Mauser C96) work on recoil from the forward motion of the bullet.

    Simply put, if the bullet does not move, the gun will not operate; the pressure itself will NOT move the barrel or the slide and the gun will not unlock.

    This was once called Newton's third law of motion (for every action there is an equal and opposite reaction) but now has been Borax freshened and lemon scented and put out as the Law of Conservation of Momentum. Still basically the same thing. Mass x velocity in one direction equals mass x velocity in the opposite direction. The bullet is small mass times high velocity, the barrel-slide unit is large mass times slow velocity, so they equal out.

    HTH

    Jim
     
  16. Old Fuff

    Old Fuff Member

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    Actually the use of “long links†to lock the barrel into battery was first popularized by the folks at Springfield Arsenal during the late 1950’s. They were trying to develop a match grade .45 for armed forces’ match teams and civilians who competed in the National Trophy Pistol Match held at Camp Perry, Ohio each year. During these early days they had to use modified service pistol parts, and to achieve a tighter lock-up they had set of barrel links with longer then normal spacing between the holes. When an armorer built a gun he would experiment to find the particular link that gave the best, but not a perfect lock up. So long as the barrel wasn’t forced or “jammed†into position this system worked.

    By the early 60’s they had developed a true “match grade barrel†that had extra metal on the hood and link-lug that allowed individual fitting on each pistol. With this system the lower hole in the link was drilled oversized and only served to pull the barrel down while the slide moved backwards. The barrel was cammed upward by the lug pushing against the slide stop pin. This was much better then the previously used “long link†which was quickly abandoned. This resulted in excellent bull’s-eye match pistols, but had one serious drawback in a service gun. If excessive fouling or dirt built up in the slide in the area of the barrel locking lugs the piece might refuse to go into battery.

    In my view the “long link†system still has a place on a carry gun (read that as “personal weaponâ€) IF IT IS CORRECTLY FITTED. If it isn’t you will get all of the problems Tuner alluded to. From the point of view of maximum accuracy a tightly fitted, lug-cammed barrel is unquestionably the way to go. However this accuracy may come at the price of reduced reliability – particularly in a dirty environment.

    One may also opt for a lug-cammed barrel that is slightly less then fully locked, which offers a compromise of a little less accuracy in exchange for some additional reliability.
     
  17. Jammer Six

    Jammer Six member

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    Jim, that's twice you've said that.

    Where does Kuhnhausen say this?

    I have both volumes, and would like to read what he says about "thrust vectors".

    Thank you.
     
  18. 1911Tuner

    1911Tuner Moderator Emeritus

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    Link Length

    Excellent! So far, so good. Many questions have been asked and answered. Kudos to BigG for his explanation to Delmar.

    The barrel and slide move straight back for a distance of about 1/10th
    inch and the barrel STARTS to unlock at that point, as the slidestop
    pin reaches the upper part of the forward curve of the barrel lug. By the time the slide has traveled a quarter inch...the barrel should be completely unlocked from the slide and in the bed, or as some call it, the saddle. When the barrel is in the bed, there should be a small gap between the top of the barrel and the underside of the slide. This gap should be a .012-.015 inch. I like to see .018-.020 inch, but that's just me. These figures assume that the lower lug is in-spec, and the link is the proper length.

    The link TIMES the event. If it's too long, the barrel is held to the slide
    for too long. The lugs can be impacted by the lugs in the slide, and they
    become "rolled" on the front. This damage can extend to actually starting
    a shearing action on the lugs...and the lugs in the slide begin to show damage as well. A link that is too long can also bring this damage about
    when the rear of the barrel lug hits the impact surface in the frame while the link is in a bind with the slidestop pin. The barrel is captive for a brief
    time, and the lugs get hit.

    On the other hand, if the link is too short, the barrel begins to unlock
    too early, while chamber pressures are still high. This can undermine
    the case head support and put additional stress on the extractor hook
    as it tries to yank the still expanded case out of the chamber.

    With the link in the In-Battery position, the radius in the hole should align
    with the radius in the lower lug at the rear and the bottom. If the link's
    hole protrudes above the lug, the link is too long, and is bearing the load
    of vertical lockup, and all sorts of bad things can occur.

    The pin hits the lug feet toward the tips instead of in the radius. The tips of
    the feet get damaged by the slide going to battery. The pin that holds the
    link in the lug begins to wallow out the hole that it's pressed into, and the
    interference fit is lost. The bent feet and sloppy action in the link delays
    linkdown timing. Incidentally, this is why letting a slide slam into battery on an empty chamber is a bad thing to do to an autopistol.

    Now, go to the front curve of the lug. When the barrel is in linkdown, the
    link doesn't lay flat against the barrel. It swings to a point that roughly
    aligns the radius of the hole in the link to the center of the convex radius
    of the lug...or just slightly past center. As the slidestop pin goes around the "corner", the pin should make light contact all the way, if the lug is correctly dimensioned. If it's not, and the pin is held away from the lug,
    the barrel is riding the link...even though its length is correct in lockup.

    Most production pistols' barrels ride the link to some degree, and it won't
    hurt anything for many thousands of rounds, and then it's usually just a
    slight loosening of the pin. Since these pins come in oversizes in .001
    increments, we can fix the problem with the next size up.

    In this situation, we can go to a slightly shorter link, provided that the
    link isn't being stretched as the barrel links down, and it doesn't get the
    pin in a bind as it goes back around the corner toward vertical lockup.
    The hole in the link can be slightly BELOW flush with the lug...just not above flush. .003 inch shorter seems to be about the limit in any case,
    due to the stretching forces against the link as the barrel comes to full
    linkdown. In some instances, we can't go to a shorter link due to the dimensional tolerances of the impact surface in the frame to the backside
    of the lower lug. Most of the time, we can.

    Going to a slightly shorter link has one distinct advantage. It can reduce
    a slight stem bind condition during the feeding stroke. Whenever you run
    into a failure to return to battery, and you notice a crescent-shaped mark
    on the case just below the mouth, you have stem bind. By going to a
    slightly shorter link, you delay the barrel rise for a few degrees in the
    arc. When the round is stripped from the magazine, it hits the barrel
    throat at some point, and this causes the barrel to move forward. When
    the barrel moves forward, it also begins to move UPWARD, due to the
    link's influence on the barrel, when the barrel rides the link. The longer the
    link, the faster it swings upward, and the higher it will be in relation to the
    barrel's forward movement. It's a mechanical ratio. Think of a pole vaulter
    when he sticks the pole in the vaulting cup as he races toward the bar. The higher up on the pole his hands are positioned, the faster he will rise,
    and the higher he will vault. He is the barrel riding the link.

    If your barrel is riding the link, and you want to make the pistol feed
    more smoothly...try going to a slightly shorter link. There is a limit to
    how MUCH shorter you can go. To find it, remove the bluing from an old
    slidestop pin, and color it with machinist's layout fluid, or a felt-tip marker.
    Install it through the link with the slide and barrel on the frame, and
    leave the arm hanging vertically. Leave the recoil spring and plug out of the slide, and push the slide fully rearward. Push the barrel down and
    back into the frame and hold it there with moderate pressure. The slidestop should swing freely without binding. A very tiny bit of bind is
    okay, but ideally, it should swing free of its own weight. If it binds, remove
    it and see where the bluing is removed. If bare metal is showing at the
    front, the link is too long. If it's at the rear, it's too short.

    Blueprint specs call for a center to center length of .278 on the link. I've
    found that a .275 link can be used in most production pistols. This is
    the essence of fine-tuning, and helps us to understand why some pistols will feed almost anything, while others are finicky about the overall cartridge lengths. The link plays a part.

    Cheers!

    Tuner
     
  19. bigjim

    bigjim Member

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    Thanks guys,

    Tuner, Jim, Old Fuff, BG,

    I have several guns part now and I am looking at what you have all mentioned and am trying to understand it. Thanks a lot!


    I have printed Tuners last post and I Am using it as a bench mark reference since it is quite clear. Does anyone else disagree strongly with any of his assertions?

    I am planning to keep what we come up with in each of the clinics and post them back here as a compilation.
     
  20. 1911Tuner

    1911Tuner Moderator Emeritus

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    Links Revisited

    Mighty welcome bigjim.

    Another point that I forgot to mention is that, when the barrel is fully
    down, the bottom of the barrel isn't supposed to lay in full contact with
    the curved part of the frame. CORRECTLY fitted, the link should
    be holding the barrel just barely off the curve...about the thickness
    of onion skin. Very few late production pistols do this, and the barrel
    lays in the curve. It doesn't seem to hurt anything, so it's probably the
    result of the manufacturers finding yet another shortcut in the assembly.

    At this point, it's mainly trivia...but one that many don't realize.

    Keep it goin'!

    Tuner
     
    Last edited: Apr 1, 2009
  21. Old Fuff

    Old Fuff Member

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    Perhaps I should explain that in a stock .45 1911 or 1911-A1 pistol with a standard GI barrel and link the slidestop pin and lower lug do not play any part in camming the barrel into a locked position. This is left entirely to the link, and when the slide is in battery the barrel “floats†to some degree at the breech end. Prior to the late 1950’s there was only one barrel configuration and one size link.

    The development of using specially sized links and/or the lower lug on the barrel as a cam surface to position (or lock) the barrel into the slide while the pistol was in battery came about because military arsenals at Springfield and Rock Island, as well as several well-known civilian pistolsmiths, were trying to develop the best possible bullseye match pistol, not a service or personal weapon. The man in charge of most of these adaptations was an engineer at Springfield named Gene Taylor. He probably knew more about the Government Model .45 pistol then any man other then John Browning. At the time he had the full resources of both the arsenal and Colt’s behind him, and I was fortunate enough to learn a lot of what I know from him.

    Correctly fitting a “match grade barrel†to an individual pistol (and once fitted a barrel does not usually interchange between different guns) requires special tooling, fixtures, and gages – most of which are available from Brownells. It also requires knowledge and expertise. None of this is beyond the capability on an ordinary gun owner with basic mechanical skills, but in terms of doing one – or several guns – it is overly expensive in terms of the learning curve and equipment costs.

    That said, I believe that most of the members of this forum are more interested in the Government Model as an optimal personal weapon, not as a match pistol. The requirements for both are different. Where the match gun is primarily designed to offer the best possible accuracy a weapon should emphasize operational reliability – under any circumstances and in any environment.

    Tuner’s explanations concerning the proper fitting of a slidestop cammed lock-up are, in his usual fashion both detailed and correct. Anyone can benefit from an understanding of what happens, and why it happens. One may also notice that things are not as simple as they might first seem, and that a small error in fitting may have some short or long term effects in the way the pistol functions (or doesn’t as the case may be). This knowledge may help one diagnose the cause of some malfunctioning and provide a clue as to what corrections should be made to cure it. However simply disassembling the gun and going to work may result in more and possibly worse problems. There is no substitute for experience. Anyone who might have to use their pistol as a weapon should never forget this.
     
  22. bigjim

    bigjim Member

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    Thanks for the input Old Fuff,

    That really is the rub isn't it? I understand what you are saying in regards to needing experience to do these things right. The trouble is no one is born with this knowledge. Even the worlds best smiths had to learn at some point.

    I do think these forums and the kind of information we are generating in these clinics could make that learning curve less painful for some.

    I for one will be happy to learn things from you guys as opposed to getting a bloody nose learning by myself.

    If it serves no other purpose it can help us recognize when we are being BS'd by a pistol smith that isn't.
     
    Last edited: Dec 28, 2003
  23. romulus

    romulus Member

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    What happens if the barrel is completely off the frame barrel bed, meaning more than merely an onion skin's worth of difference? After reading Kuhnhausen I figured that this point of contact had to be exact. If the gap is significant, what are the repercussions?

    Thanks
     
    Last edited by a moderator: Apr 1, 2009
  24. 1911Tuner

    1911Tuner Moderator Emeritus

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    Point/Counterpoint

    Old Fuff has nailed me down again.:D He's made a point about the
    barrel link that, looking back, he tried to make once before, but I didn't
    see it. Haste, and my habit of checking these posts in the wee hours
    before I've poured enough coffee down my neck to be able to see.
    In fact, I had a rather heated discussion with Jim Keenan on this very
    point about a year ago. He was referring to fitted barrels, while I was
    taking Fuff's point of the barrel pivoting on the link.

    Yes. Up to a point, the barrels rode the links instead of camming into lockup via the lug/slidestop pin, BUT...when in vertical lock, the link should be flush with the barrel lug. That some weren't was likely either the result
    of hasty assembly, or a misunderstanding of what the return to battery impact would do to the tips of the lower lug feet instead of in the stronger
    area of the radius. Most of them didn't stand above flush, and was the result of the bottom lugs being in-spec or very close. Most production pistols barrels today ride the link to a point just prior to lockup, and some are partially supported by the link, but this condition will contribute to early failure of the link, the linkpin, and its hole in the lower lug. Given enough use, it can even wallow out the slidestop pin hole.

    Keep in mind that,in the beginning, these pistols weren't designed with
    100,000 rounds in mind without arsenal attention. Even 50,000 would
    be stretching it. Most were rebuilt much sooner.

    When the link is above flush, the innacuracy comes from having only one
    narrow point of support. When the bullet engages the rifling, it causes
    the barrel to torque, and if there is a fairly loose fit at the hood, it would
    rotate. Unless it rotates exactly the same from shot to shot, the groupimng
    potential opens up. A flush link with full support across the lug works to limit that rotation somewhat, depending on how much difference there is between the size of the slidestop pin and the hole in the link. Anyone who has fired a rifle from a sandbag very much can attest to the effect that canting the rifle has on groups. Since most pistols prior to the end of WW2 were ordnance spec with more generous tolerances than their pre-war counterparts, the above-flush link's effect would be greater. This, along with hasty arsenal refurbishes, doubtless contributes to some of the accuracy issues with WW2-era GI pistols.

    One final point on the barrel linkdown timing. If the barrel unlocks just at
    the right time, when pressure is low enough to allow the case to move
    easily, but with enough residual pressure left in the chamber, the pistol will
    function very well without an extractor. After playing with this for a while, I've come to the conclusion that this is more likely to happen when the
    barrel timing is a little late. Tming the linkdown a bit earlier with a.003
    shorter link returns the gun to needing the extractor to get the case out of
    the chamber. That's less than the thickness of a sheet of notebook paper.
    Amazing what a difference such a little dimension can make.

    Cheers! I promise to read more carefully in the future. Still wonderin' if
    Old Fuff is gonna reveal his true identity.:scrutiny: I think he's somebody famous.:cool:

    Cheers!
    Tuner
     
  25. 1911Tuner

    1911Tuner Moderator Emeritus

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    Repercussions

    Romulus asked:

    What happens if the barrel is completely off the frame barrel bed, meaning more than merely an onion skin's worth of difference? After reading Kuhnhausen I figured that this point of contact had to be exact. If the gap is significant, what are the repercussions?

    Possible feeding problems, depending on how far it's up off the bed,
    and how far forward of the frame's ramp the leading edge of the throat is.
    If it's high enough, the bullet nose hits the edge instead of making a smooth transition into the throat. Sounds like the lower lug feet are too long, or there is a burr on the side(s) of the lower lug that's stopping the barrel from going to bed. Also a slight chance of the link's pin not being centered in the lug, and one side is making contact before the barrel is down. Hard to say without seeing it.

    Have a look and get back to us.

    Tuner
     
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