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Thread: 1911 Clinic

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  1. #1
    Join Date
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    1911 Clinic

    After a discussion/Disagreement on another thread in regard to early unlock timing and the phenomenon of gas and powder blowback through the breech...I thought I'd take a little time to address it in the interest of understanding this marvelous Browning Brainchild.

    First...Understand that the barrel can't unlock while the bullet is present and the barrel and chamber is pressurized.
    Ain't gonna happen...and if the timing is so early that the link tries to disengage the barrel from the slide, the link will
    stretch and probably fail in very short order. (The exception would be that the link stretches to the point of delaying linkdown until the bullet has left. Most of the time, this causes problems with delaying linkdown and drop timing too much, with resulting damage to locking lugs...but that's meat for another clinic.) A little study on how the 1911 achieves its locked breech...when it locks...and when and how it unlocks will make it clear. The breech locks when the gun fires, and unlocks when the pressures have dropped. The link doesn't "unlock" anything. It only draws the barrel down and out of the slide AFTER unlock has occurred.

    Read that again and think about it. The "Locked Breech" 1911 is not locked until it fires. The term "Locks up like a vault" and, Locks tightly into battery" are technically incorrect, and misleading. If the barrel is closely hand-fitted, it's wedged into battery via an interference fit in the related parts...but it is NOT locked.

    So...How does the gas blowback happen?

    This condition is rare. So rare, that I've only seen it happen with a half-dozen or so pistols in over 40 years. It requires that the timing be just perfect, with a very narrow window of opportunity in order to happen. A thousandth of an inch or two greater center-to-center distance in the link, and it won't happen. The mechanics of the event are simple, if we remember that any force that occurs in nature tends to follow the path of least resistance.

    The start of the linkdown phase begins at roughly .100 inch of slide and barrel travel. This will vary for several reasons, but is generally controlled by a combination of varying dimensions within the gun. Also known as "Tolerance Stacking."
    No need to go into great detail other than to say that the slide's installed height relative to the slidestop's crosspin hole
    and the link's distance from hole center to center are the main factors. Lower lug geometry also plays a role, but a smaller one. If the linkdown begins at say...about .090 inch of slide/barrel travel, you 're very close to seeing gas blowback. In these, you will probably notice that you can remove the extractor from the slide, and the gun will continue
    to extract and eject, albeit erratically. The reason being that residual gas pressure within the barrel that hasn't had time to escape. Note that missing extractor function can occur without apparent gas blowback, but if the gun will function without the extractor, there has to be some amount of blowback. It's just not enough to notice. In fact, there's a amall amount of blowback even in a perfectly timed gun. That's where all the carbon and other crud in the ejection port and on the breechface come from. It happens after the bullet has left, and the case has sprung back...and blows past the walls of the case and into the breech.

    This residual gas pressure occurs just at the instant of, or just after the bullet breaks into the air. In some, it may occur
    when the base of the bullet is in the muzzle crown, where the rifling is cut on a taper...and technically hasn't actually cleared the barrel completely. The gasses impinge on the bullet base, and are forced to blow out sideways though a narrow gap...such as the barrel to cylinder gap on a revolver. This gap only lasts a fraction of a nanosecond...and here lies the narrow window for blowback through the breech.

    Pressures are low enough to end the "locked breech" part of the function, but a small volume of gas and pressure is still present. The slide is moving, and the link is drawing the barrel downward...and the breech is open...though not by very much,Primary extraction has begun. The case walls have sprung back... the walls have broken free of the chamber, and the residual gasses have found a path of lesser resistance than escaping sideways past the bullet base and muzzle crown...and they "follow" the empty case as the extractor pulls it clear. Here's they've hit another set of paths of greater and lesser resistance, since the case can't contain the volume of gas, and they again follow the path of least resistance, and escape into the now open breech area. It would appear that they're blowing straight back, but in reality are blowing in all directions. Up...down...sideways...diagonally...forward, and backward...the same as any force vector.

    The fix for this situation is often as simple as a slightly longer link...maximum of .003 inch... or elongating the bottom of the link's hole to delay the start of linkdown by a couple of thousandths of an inch...again, for a maximum of .003 inch.

    Here endeth the lesson.

  2. #2
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    Good post Tuner. I am beginning to have a better understanding of the 1911 after reading (an rereading) many of your posts.

  3. #3
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    Another great lesson from the Mr. Meogi of 1911`s.
    As Hunter said. I am also learning a lot from your fine lessons.
    It seems to me you read some here and read some there and all of a sudden it starts coming together and make some sense. A little anyway.

    Jay

  4. #4
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    I Thank You.
    No free man shall ever be debarred the use of arms.
    Thomas Jefferson

  5. #5
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    Thanks Tuner! You da' man!!

  6. #6
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    I have been shooting 1911's for over 40 years, and I still know so little...thanks Tuner...now, for a question...folks I know who have had barrels fitted by Wilson, or by local gunsmiths report that barrel fit is not only tighter, but that it takes significantly more "energy" to rack the slide...IOW, more difficult, but doable...is this to be expected?

  7. #7
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    Barrel

    Quote Originally Posted by Dustoff '68
    I have been shooting 1911's for over 40 years, and I still know so little...thanks Tuner...now, for a question...folks I know who have had barrels fitted by Wilson, or by local gunsmiths report that barrel fit is not only tighter, but that it takes significantly more "energy" to rack the slide...IOW, more difficult, but doable...is this to be expected?
    Howdy Dustoff,

    Well...it depends. Unless I miss my guess, the extra resistance is right at the beginning, when you're trying to pull it out of battery. That's a result of a
    tight fit between the hood and the breechface, which pushes the barrel lugs hard forward into the slide lugs. Added to a tight fit in the vertical plane...tight fit between the lower lug and slidestop pin, which forces the barrel lugs hard into their slots in the slide...but most of it is due to the tight horizontal fit. It'll free up a bit with use, but you can make it a little better
    in a few minutes without losing any of the precise fitting and the accuracy that it affords.

    Mix up a little "Slurry". The recipe is around here somewhere. Coat the locking lugs with it, and assemble the gun. Hand-cycle about 50-75 times.
    Rinse well with carburetor cleaner...oil...and see if it's not a lot better.

  8. #8
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    Well Johnny, you've piqued my interest. I certainly agree with this last post re relieving the pressure, but I've never given a thought to doing it at the top. Whenever I build a BE 1911 and it's a bit snug at initial racking, I usually pull the slide stop and see if the hood lockup is too tight...and if it is I'll just mirror it a bit until it feels right. If it doesn't feel too tight, I then pay attention to the lower section. I'll either polish a little more on the lower lugs, or occasionally I'll do a Marine Corps Cut on the pin. I really don't like to elongate the link pin hole.
    Working on the lower lugs accomplishes the same relief as your description re the top lug abrasion, if it's done in moderation, but I think I'll just try your way the next time I have one that qualifies for the procedure. It sounds very interesting!

    Bob

  9. #9
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    re:

    Hey Bob! Thought you'd abandoned us.

    The hole elongation works pretty well within its limits. (.003) and doesn't thin and weaken the slidestop pin the way the Marine cut does, and a link is cheaper than a slidestop. I've used both, but they accomplish the same thing...Delaying the linkdown for a tick longer.

    The slurry in the lugs is one that I've used several times, and it works nicely without breaking out the stones. You can also use it on the lower lug to relieve a little tightness in the vertical. Great stuff!

    CLP Breakfree and J&B Bore Cleaner. Mix to a soup that just sags off the end of a screwdriver, but doesn't drip. Let it stand open overnight...remix before use. Use it liberally. Does the trick on
    rails too. Makes'em slick like butter.

  10. #10
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    Nope, I'm still here. I monitor this forum every day or two but between you and a couple of others, you have the situation well in hand.
    I agree about the link/vs pin weakening, and I rarely do either. My preference is to tweak the bottom lugs, or if I have a reason not to do that, tweak the top lug channel. I prefer the lugs though, because it's too easy to get one of those 2 top points a tad shorter than the other.
    My slurry is similar to yours, only I just use honing oil with the JB. I have a series 80 Colt coming in tomorrow for a complete build and it may get the slurry treatment if it's indicated.
    I've been a bit busy with trying to figure out what the heck my dog is allergic to. I'm giving him some raw meat on bone, along with a bunch of chopped veggies and cottage cheese. I've taken him off a steriod and put him on Moducare to adjust his immune system also. We'll see.
    It was really comical, watching his first encounter with a bone with raw meat on it. He did good, though! And I hope to be a bit less busy with him so I can concentrate on these 1911's. I've been pretty tied up with testing that new AA 22 conversion unit but it's all done now. They tell me production won't be for "a few months." But it's going to be a winner.

    Bob

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