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Thread: Recoil Function

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  1. #1
    Join Date
    1st June 2004
    Location
    Lexington, North Carolina...or
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    Recoil Function

    In response to one of three questions:

    Without going into small details on vectors of force...the best way to understand the recoil cycle is to first study the locked breech system itself.

    A few things to keep in mind are:

    The barrel isn't supposed to lock on the link...at least not in a properly fitted gun that is in-spec. The link's sole function is to unlock the barrel.

    The recoil spring has very little to do with unlock timing. It has almost no influence on the slide's initial movement, and it has nothing to do with
    containing chamber pressures. The mainspring has more influence on
    delaying the slide's initial movement, and is a function of the slide's
    mechanical leverage in recocking the hammer. Remember the point of
    the slide's "Initial Movement." It will have more meaning soon.

    The barrel and slide are locked together by a series of lugs and slots
    that mesh in the horizontal plane. Vertical lockup is achieved by the
    lower barrel lug camming upward on the slidestop pin, and is a topic for another discussion. Static on the bench, the breech isn't locked. "Lock" begins when the vector of force is applied and bullet movement begins.
    Prior to that, the only horizontal "lock" is provided by the recoil spring's
    tension.

    As the bullet is forced through the bore, the barrel is pulled forward. At the
    same instant, the slide is hammered backward in the equal and opposite reaction that we've studied as one of Newton's laws of motion. This
    vector of force is applied equally in all directions, and the barrel and slide are in a condition of isometric lock...but this ends in a nanosecond
    as soon as the bullet begins to move.

    The vector of force gradually becomes unbalanced with bullet movement,
    and the faster the bullet moves, the more unbalanced it becomes.. and the force follows the path of least resistance...The slide. The slide, due to its greater mass, moves slower than the bullet, and because of that mass, pulls the barrel...bullet and all...rearward with it.

    Slide and barrel move in a straight line together for approximately 1/10th of an inch. The link pivots on the slidestop pin and upon reaching a point in its arc determined by its length between hole centers, starts to change
    the barrel's linenear movement and forces it to start changing direction to downward. The unlocking phase begins at that point. The point can be physically seen by looking at the lower lug's shape at the front...where it forms a radius that allows the barrel lug to fall off the slidestop pin. The barrel's downward movement continues until the slide has moved one-quarter inch, and the barrel is linked down completely and on the frame bed. Complete unlocking occurs at some point before this quarter-inch point is reached, but that's the point that the barrel must be
    in the frame bed so that the slide can continue to move without contacting the barrel's locking lugs, assuming that the barrel's impact surface in the frame is correct in relation to the rear of the lower lug.

    The recoil cycle is completed by the momentum imposed on it during that first 1/10th inch of movement. By the time that the unlocking phase begins, the bullet is gone, and the "Equal and Opposite" reaction to
    the bullet is gone with it...and Conservation of Momentum has taken over
    to complete the cycle.

    This is a point of contention in Jerry Kuhnhausen's theory of "Balanced Thurst Vector" in which he states that the slide begins to move AFTER the bullet exits, when the balanced thrust vector that pulls the barrel and slide in opposite directions is broken by bullet exit. This...simply put...can't be. If the bullet exits the muzzle BEFORE the slide moves...the slide won't move. The slide has to move while the bullet is still in the barrel. As noted, this distance is very short...but it has to move before the bullet exits because without the bullet to act as a means to redirect the vector of force against the slide, the slide will stand still...or at best...move very little as a result of any remaining expanding gasses remaining in the bore after the bullet exits.

    After barrel linkdown, it's a simple matter of the slide obeying another of Newton's laws, and remaining in motion until forced to stop by an outside influence....the impact surface in the frame. The recoil spring has compressed, and it's stored energy forces the slide to return to battery.

    Next: A recoil spring study.

  2. #2
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    Oh, no!! PHYSICS!!!!! AAAAAAARRRRRRHHHHHHH!!!!!!!

  3. #3
    Join Date
    1st June 2004
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    Lexington, North Carolina...or
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    Physics

    Quote Originally Posted by stans
    Oh, no!! PHYSICS!!!!! AAAAAAARRRRRRHHHHHHH!!!!!!!
    BWAAAAAAHAHAHAHAHAHA!

  4. #4
    Join Date
    4th October 2004
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    Used to be N.C.
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    Yay?

  5. #5
    Join Date
    21st December 2004
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    New here. Friend asked me to stop by. Doing some high speed pics maybe this weekend if things fall right will have some high speed photos of bullet at the end of barrel, half way out and all the way out. With markers on slide to show movement of slide to frame.
    STEVE

  6. #6
    Join Date
    1st June 2004
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    Lexington, North Carolina...or
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    Photos

    Hey Steve! Welcome aboard. The pictures would be great!

    On the one you've posted...unless the light and shadows are playin' tricks...
    looking at the muzzle, rear of the slide to frame position, and the barrel in the port...It appears that the slide has moved almost to the point of complete barrel linkdown with the bullet about 4 inches out. Assuming a muzzle velocity of 800 fps, that would make the slide's movement there occur in
    roughly 1/2400th of a second. Figuring that the bullet has moved a total of
    about 8-9 inches to reach the spot shown...and plugging in estimated average bullet velocity on its trip from chamber to muzzle...it would seem to
    me that the unlock/linkdown phase started at just about the point that the bullet broke free of the barrel...or maybe an inch out. Since the slide and barrel move together for roughly .100 inch when unlocking begins, the time frame would appear to be about right for that to occur, since it appears that the slide has moved twice times the distance needed...about .200 inch or so.

    Lookin' forward to the stop-action photos.

  7. #7
    Join Date
    19th July 2004
    Location
    Seattle
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    Talking Cool!

    Oh, this is going to be a great thread!

    "I'll fire the gun, and you take the picture. When you hear the gun go off, take the picture really, really fast!"

    Sounds like a plan to me, but your picture-taker is faster than mine!

  8. #8
    Join Date
    1st June 2004
    Location
    Washington State
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    Would like to see pics at the different stages of fire.........

    Just pulled the trigger- moment of cartridge ignition

    A split second after that, after ignition but while the bullet is still in the barrel.

    Then one other with the bullet just leaving the barrel...........at the end, or just showing at the muzzle.

  9. #9
    Join Date
    14th October 2004
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    mid Michigan
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    Wow

    thats soem picture taker. Tuner you amaze me
    Bear's Story .

    If you have no money and few possesions, if you have a dog you are still rich.

  10. #10
    Join Date
    4th October 2004
    Location
    Used to be N.C.
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    Welcome

    Welcome jpl-labs and thanks in advance. Hope you can provide those pictures, also that you enjoy the site and people.

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