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Thread: how does the longer barrel increase velocity?

  1. #1
    Inactive Member

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    Default how does the longer barrel increase velocity?

    some people saying longer barrel can keep valve open longer due to internal pressure and offer more air when it's firing. that's why increase the velocity.

    but some other poeple saying more air can be only produced by heaver hammer or spring and has nothing to do with longer valve opening time. also the longer barrel doesn't make valve opening time longer.

    very confussed. which one is true?


    if the barrel length doesn't work with valve opening time. then after every shot. the amount of air should be always stay the same. no matter what barrel length has been used.

    but longer barrel should have more resistance force from rifling. if the amount of air pressure stays the same behind the pellet after each shot. if we use 50" barrel. will that make velocity higher or lower?



    after pulled the trigger.
    hammer hits valve.
    valve opens and release the certain amount of air to push the pellet.
    pellet traveling in the barrel and the valve keep open and release air due to chamber pressure until the pellet get out of the muzzle. the valve closed.



    if above theory is wrong. so. can i define following theory:



    the longer barrel DO NOT keep valve open time longer but only use the same amount of air more efficiency to increase the velocity.


  2. #2
    Sharp Shooter

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    Read " From Trigger To Target" and it will all make sense.

  3. #3
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    It doesnt. The barrel has nothing to do with closing the valve. A measured amount of "compressed" air is released by the hammer into the chamber which expands rapidly to force the pellet out. The barrel length determines how flat the initial trajectory is. Also a long barrel will slow down the pellet so much it will be lucky to exit the barrel anyway. Remember the South African chappie who designed the gun the Iraqi's where having brought in bit by bit, really long barrel, he's dead now so dont go messing about with valving. Think I need anotyher Whisky.

  4. #4
    Marksman
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    longer barrel makes full use of all the air getting dumped by the valve...in PCPs the release is slower than in springers...hence in springers a barrel beyond about 7 inches makes no diff...

  5. #5
    Sharp Shooter

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    100% correct Guido. 22 cal airrifles optimise the air better than a 177 hence more shots with 22 calibre airguns from the same fill pressure.

  6. #6
    Marksman
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    Sorry to differ Brian but the barrel length does make a difference to how long the valve stays open due to the back pressure caused by the pellet.
    And barrel length does determine the flatness of the trajectory simply due to the fact that it increases velocity the longer the barrel [obviously only up to a point]

  7. #7
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    Well I stand corrected but I would think that 200Bar on one side of the valve would close it off a damn site faster than a reducing pressure would hold it open. Try cocking an EV2 then firing it without closing the lever correctly. It goes BANG not SSSSSS. I agree that the initial pressure in the chamber would be approximately the same at release but as the pellet travels down the barrel the air will expand and reduce in pressure, the pellet mearly becomes a moving object which allows the air to fill the increasing void, this is not an explosive force as in a Cartridge. True, a longer barrel allows the air pressure more time to act on the pellet.

  8. #8
    MOT: Thomson Pneumatic Rifles

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    Brain and Guido are both right in places.
    A "messured" amount of air will only be released every time on firing buy a rifle equiped with a regulator, even here a longer barrel mite increase velocities by a few feet per second.
    A longer barrel does produce more velocity (abviously with a point of deminishing [?? spelling Brian] returns), "fire arms" work the same way, the longer time the expanding gasses act on the bullet/ pellet more energy can be transfered.
    Pressure is not that much of an issue, a rifle running at 150bar can produce a higher velocity than a 200bar rifle, it depends on the VOLUME of air dumped behind the pellet, the volume determans the exit pressure.
    A longer barrel is more important in Co2 rifles as it alows more expantion area and increased pressure and energy transfer.
    The larger the caliber the more EFFIECIENT the rifle becomes, ie a .45 cal air rifle with a 600mm barrel and matching "pellet" (at this size surely it qualifies as a bullet!!) can produce +- 1000fps and 550 to 600fpe.
    A military air rifle from the early 1700's shot a .51cal ball (+-238grns) at 1000fps for +-530fpe and here's the kicker, this on 500psi air thats less than 35 BAR!!
    Air is COOL!

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