Barrel Length Measuremwnts
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  1. #1
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    Default Barrel Length Measuremwnts

    Why doesn't the cylinder length count in barrel length in a revolver? For that matter, why isn't chamber length deducted from a rifle's measurement? The bullet doesn't start from the breech face.

    Bill

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    Quote Originally Posted by 9100 View Post
    Why doesn't the cylinder length count in barrel length in a revolver? For that matter, why isn't chamber length deducted from a rifle's measurement? The bullet doesn't start from the breech face.

    Bill
    1) What makes you think it doesn't.
    2) Why should it be?
    3) "The bullet doesn't start from the breech face." has no bearing on the topic.

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    If you consider both as only "parts" I would guess it's because when you're talking just a "barrel" a revolver barrel actually starts in the frame and a rifle barrel starts in the receiver.

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    Because of measuring conventions established hundreds of years ago.

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    It's actually pretty simple.

    The barrel is the length of "the tube" as measured from cut end to cut end. This is true regardless if it is a muzzle loader, pistol, rifle, revolver or shotgun.

    On shotguns that have an extended portion of the barrel that slides into the receiver the length is still measured from the non extended portion to the muzzle.

    External or internal threading (muzzle loader breech plug), chambers, extractor cuts, forcing cones etc. don't matter. It is the length of tubing from one face to another that is the measured barrel length.

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    Quote Originally Posted by Kurt Learning View Post
    1) What makes you think it doesn't.
    2) Why should it be?
    3) "The bullet doesn't start from the breech face." has no bearing on the topic.
    I think you have a misunderstanding. Bill is correct, in a revolver, the cylinder length is NOT counted as part of the barrel length.

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    Quote Originally Posted by Scottl View Post
    It's actually pretty simple....

    On shotguns that have an extended portion of the barrel that slides into the receiver the length is still measured from the non extended portion to the muzzle...
    Don't you mean, "the length is still measured from the extended portion to the muzzle"?

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    Quote Originally Posted by 9100 View Post
    Why doesn't the cylinder length count in barrel length in a revolver? For that matter, why isn't chamber length deducted from a rifle's measurement? The bullet doesn't start from the breech face.

    Bill
    I believe I have found the source of my confusion.

    There are two parties interested in barrel length.
    The manufacturers and consumers in one camp and the regulators in another.

    I was considering the BATFE method of measuring barrels. Their concern isn't ballistics, but conceal-ability.

    One can simply drop a dowel down the barrel of an unloaded firearm, from the muzzle end until it contacts the closed bolt/slide. Measure that length of the dowel and you will have the barrel length.
    This usually includes the chamber.
    The revolver is measured the same way if it has revolving barrels like a pepperbox.

    I assumed the BATFE would be consistant and rational in including the chamber as a part of barrel length as the cylinder length affects conceal-ability. Silly me. That's too rational.
    If the revolver has a cylinder separate from the barrel, the cylinder is not included in the measurement.

    Muzzle to breech face measurement is very rational for non-revolver manufacturers and consumers that are interested in balistics, parts ordering, aesthetics, sight radius, weight, balance, etc.
    Imagine Winchester/Remington/Howa screwing various .30 caliber barrel blanks of the same length, into receivers. Then having to determine, and advertise the spectrum of barrel lengths if measured from the front of the chambers as they are cut. .308, .30-'06, .300 Win Mag, .300 Norma, .300 H&H, etc.

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    It seems to me that from a ballistician's viewpoint that barrel length should be the distance the bullet travels while sealed to the tube. I guess you can still argue about freebore and pressure relief through ports, but those are minor side issues.

    Bill

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    Quote Originally Posted by 9100 View Post
    It seems to me that from a ballistician's viewpoint that barrel length should be the distance the bullet travels while sealed to the tube. I guess you can still argue about freebore and pressure relief through ports, but those are minor side issues.

    Bill
    You are correct- from a ballistician's point of view.
    But the ballistician takes a back seat to others in many cases.

    The machinist/manufacturer may just want to know what length of barrel to grab before finishing. Ten different barrels will have 10 different lengths of bullet travel after being chambered for 10 different cartridges.

    The accountants will have a different point of view. Their belief is that a 24" barrel cut into 4 equal lengths yields four 6" barrels. A machinist will tell you it doesn't. Kerf/waste.

    Then the advertising department will look at your work. You've taken a 35" barrel, cut it into 3 equal length pieces and installed them on Colt Peacemakers. After finishing, they may be only 11.5 inches. But the advertising department will sell them as 12" Ned Buntline Specials.
    (Go to your lumberyard and measure a 2"x4" and see what you get.

    The ballistician may take a back seat because his knowledge and investigations are more complex than some of the other disciplines.
    First of all we don't know what the ballistician may be looking for.
    I would question the speed of a bullet coming out of a 16" barrel bolt action rifle compared to that of a 16" barrel revolving rifle. And although we've already established that the two 16" barrels would be of different length, we haven't accounted for the gas loss between the barrel and cylinder on the revolver.
    There are other factors to consider.
    Is the barrel ported? Any bleeding of gasses may reduce velocity.
    What if the firearm is a gas operated repeater? Doesn't the removal of gas pressure from the barrel affect exterior ballistics.
    Then to a lesser degree, what about the motion of the barrel? The barrel, slide and entire pistol may begin to move rearward as the bullet moves forward. The result is that a bullet travels less than 4" to exit a barrel that has 4" of length between the bullet and muzzle.

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    Quote Originally Posted by awander View Post
    Don't you mean, "the length is still measured from the extended portion to the muzzle"?
    No, because in this case the extended portion forms part of the bolt raceway inside the aluminum receiver. The photo below of a barrel from a Winchester semi-auto shows what I mean.

    sx4_barrel.jpg

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    The legal defined barrel length is measured with a rod against a plug or standing breech ,and includes any modification of the muzzle permanently attached.A revolver is measured differently,and excludes the cylinder.

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