The Gap Between The Cylinder And Barrel

Discussion in 'Revolver Handguns' started by Squirrel, Aug 21, 2008.

  1. Squirrel

    Squirrel New Member

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    I am not any kind authority on this, but from what I understand there is some kind of small gap between the cylinder of a revolver and the barrel; and that this gap is big enough that the the gas discharge from it is what prevented the revolver design from becoming popular for rifles. If this is so what keeps the bullet accurate as it crosses this gap so early on in its flight?
     
    Last edited: Aug 21, 2008
  2. RL357Mag

    RL357Mag New Member

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    Perfect alignment between the cylinder bore and the forcing cone. Over time this alignment is disrupted due to play in the lock-up of the cylinder. Several worn parts can contribute to this, and the most obvious indication of improper cylinder lock-up is lead splatter - this happens when the bullet is slightly off-axis with the barrel and is shaved on it's way into the barrel (forcing cone). In early brass framed revolvers, the frame would actually stretch, thereby creating problems with misalignment and excessive tolerances between the cylinder and forcing cone gap. This gap should ideally be only a few thousanths of an inch at most. I don't know if these problems are what prevented revolving carbines from becoming popular, so much as the design was actually dangerous. The support hand on early revolving carbines should not be placed forward of the cylinder to support the rifle, or gas burns would result - and in early black powder carbines, chain fires or multiple discharges would inflict serious injury. I had the unfortunate experience of a chain fire with a black powder revolver many years ago and had a .44 lead ball hit my supporting-hand thumb - it's NOT a pleasant experience!
     
    Last edited: Aug 21, 2008

  3. genie

    genie New Member

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    Look at the Gap

    Squirrel, if you hold your revolver up sideways to a bright light, you can see the gap between the cylinder and barrel. It typically may be on the order of about 0.002" wide; that's the diameter of a human hair. The larger the gap (cheaper, poorly constructed revolvers) the larger the amount of high-pressure gas which escapes during firing. This escaping gas, especially in magnum calibers, constitutes a safety hazard to human parts, fingers, and such, held closer to the firing gun than a foot or so away. Occasionally, misalignment between the chamber and barrel causes fine slivers of metal to be shaved off and spat out sideways.

    It is because of this gap that revolvers cannot be effectively "silenced", using a more-correctly referred to term, "suppressed".
     
  4. Squirrel

    Squirrel New Member

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    When I was in the Atlanta History Museum, which predictably has a massive section on the Civil War, they had a whole section on early breech loading and repeating rifles, by the revolver rifles they said that the problem was that there would be a large gas discharge right next the operator's face; because the way a rifle is held, the cylinder is much closer to the face.
     
  5. RL357Mag

    RL357Mag New Member

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    That's possible also - but don't forget about the detacheable shoulder stocks made for colt revolvers. The concept was in use long before the revolving carbine came into being.
     
  6. Bob Wright

    Bob Wright Member

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    The shoulder stocked revolvers were held differently than rifles. With a rifle, the off hand extends out to support the rifle at the fore end. With a stocked revolver, the supporting hand is held under the butt of the revovler. If not for the first shot, then for succeeding shots!

    Barrel/cylinder gap has always been a bit of contention for many folks, but I just accept it as a fact of life. None of my animate targets ever knew the difference.

    Bob Wright
     
  7. RL357Mag

    RL357Mag New Member

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    One should NEVER use the off hand to support the fore end on a revolver/carbine. The ever present danger of a chain fire dictates that the off hand always be kept behind the cylinder. I suspect many fingers and hands were blown off learning this lesson the hard way.
     
  8. c3shooter

    c3shooter Administrator Staff Member

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    The cylinder gap generally runs .004 to .006 Less than that, the weapon is likely to bind when it gets hot, and parts expand. OLDER top break revolvers are even greater.

    Want to improve accuracy? Pick a bullet long enuff that when the base is still in the charge hole of the cylinder, the front is entering the rifled portion of the barrel. 125 gr .357 are short, and not as accurate as 165 gr bullets. Yes, I know there are other factors that enter the equation. GOOD timing (the alignment of charge hole with barrel) is critical.
     
  9. Bob Wright

    Bob Wright Member

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    I used to demonstrate the effect of blast at the barrel/cylinder gap to novice shooters:

    Using a used target, tear a strip about two inches wide and 12~18" long, Using a full power .357 Magnum, or equal, drape this strip across the top strap of the revolver so it hangs down roughly centered on the gap. Then fire the gun. The results usually blow the paper to shreds, and make a lasting impression on the novice.

    Bob Wright
     
  10. Dillinger

    Dillinger New Member

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    Holy Crap! I think you and my dad used to get your firearms instructions from the same place. That is almost EXACTLY what he did to show me the seriousness of escaping gas from his revolver on the first time he took me shooting with it. He used an old tobacco pouch cut in half, but I still remember that "demonstration" today.... :D

    JD
     
    Last edited: Aug 25, 2008
  11. RL357Mag

    RL357Mag New Member

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    It REALLY gets interesting when you shoot a revolver that is out of timing...another reason I don't use public outdoor ranges.
    Also, if anyone is considering shooting BP revolvers - DO NOT FORGET TO APPLY GREASE OVER THE BULLETS! That's a mistake you will NEVER repeat
     
  12. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

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    A small gap is needed to allow the cylinder to rotate freely at all temperature extremes. Yes, steel expands when hot (even high quality steel). A small amount of gas escapes from the cylinder gap when the bullet is fully in the barrel (except with Nagant revolvers). The forcing cone (the back end of the barrel) is as the name implies, cone shaped. It funnels the bullet into the barrel allowing for a small amount of play in the cylinder.

    If you do not see a small gap between the cylinder and barrel you likely have a problem called "end shake cylinder" in S&W vernacular. This is caused by the crane/yoke (the part that holds the cylinder to the frame) being shortened by peening. This can be fixed by either stretching the crane or shimming it.
     
  13. Bob Wright

    Bob Wright Member

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    Tell me about poor timing!

    When I was a kid my first handgun was an old Colt New Service in .45 Colt. This was an ex-Mounted Police gun, originally in .455 caliber. It had seen a lot of service before coming into my hands. I did some of my earliest handgunning with this gun. After several years of use, I opened up the cylinder to eject empties and several little "half moons", or crescents of lead fell into my palm. I continued to shoot the gun that way, cocking the hammer and then rotating the cylinder into index by hand. Finally found a new hand, or pawl, to rectify the situation.

    This gun later became a customized .44 Special.

    Bob Wright