Ballistics........

Discussion in 'General Airgun Chat' started by alhucoll, Jan 18, 2010.

  1. alhucoll

    alhucoll New Member

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    Gents,

    Hope you can help me on this.

    Just switched from a HW100 carbine .22 to a HW100 FSB full length in .22 - using the same stock and scope, so only the metal work has changed.
    The carbine for food, loved the H&N FTT's and didn't miss a beat - accurate and consistent.
    The FSB using the same pellet had too many flyers for my liking (all the H&N's were sized but not weighed).

    I got a tin of the RWS Superfield, and straight from the tin the consistency and accuracy was excellent - even better once I'd sized the pellets.

    To myself, (RWS pellets made by JSB on a seperate die) are 1 grain heavier and are softer than the H&N's - my theory goes like this:

    1. The heavier weight aids in a more stable flight? Less flip when leaving the barrel possibly.
    2. The softer make-up allows the rifling to engage better, thus enabling a more stable flight?
    3. Any other ideas?

    I know that each barrel has it's own preferred flavour, but surely there is physics involved? Or is it just a case of accepting what works regardless of the reasons - personally I like to try and understand some of the reasons.....................

    Cheers all,

    Al
     
  2. RobF

    RobF Administrator Staff Member

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    could be different barrel makers between the two guns... dunno.

    but i think it's probably a host of reasons... and i'm not convinced less flip helps anything but to spot the shot landing better, as the pellet has left the barrel.
     
  3. alhucoll

    alhucoll New Member

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    I was looking at "flip" as a possible - I understand "flip" as being induced by the air immediately behind the pellet when it's released from the barrel.

    The blast of air immediately behind the skirt catching up with it? If the only air is behind it, theoretically the pellet is beyond influence.

    A tighter fit of the pellet to the bore should have less turbulent air passing by as it exits from the barrel and thus influencing it's flight less when compared to a looser fitting pellet as more air has passed by causing a more turbulent atmosphere around it as it leaves the bore?

    Would the lower air turbulence on exit of the barrel have that greater effect?

    Just theorizing, but beginning to lean towards the "softer" pellet base.

    ATB

    Al
     
  4. Charlts

    Charlts Getting dusty

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    If it's more accurate just be glad that you've pleased the airgun pixies, if anyone mentions words like physics, fluid, dynamics, turbulance or anything else made up, then it means they don't understand!:D:D;)
     
  5. alhucoll

    alhucoll New Member

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    That's me screwed!
    I'm a Mud Engineer who works with: fluid, dynamics, turbulance, physics and hydraulics!
    If you need a well drilling, I can do it - just don't expect me to explain the relationship with all the fields to get the desired effects - it's all a compromise........................................hang on :)
    Just think Armageddon - I'm one of them (not Brucey 'cos he doesn't wear a yellow topper) but I've worked with those characters!

    So the theory is a theory then - the strange man in the mirror asked me the questions......................:cool:
     
  6. alhucoll

    alhucoll New Member

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    If you need an answer ask your ARRSE:
    Courtesy of Gun_Nut from ARRSE http://www.arrse.co.uk/

    "Flip is not what you describe.
    In any rifle, the shock of firing causes the barrel to vibrate like a tuning fork. If the pellet exits the barrel on an upward motion, this is 'flip' or more accurately 'positive compensation'. If it is going down it is 'negative compensation'. In general, the best accuracy will come when the pellet exits at a 'nodal point' when it is neither moving up or down. Centerfire shooters can do this by adjusting the size of the powder charge. Some benchrest guns also have a 'tuner', which is an adjustable weight on the end of the barrel. In an airgun, the best way is to change pellet weights until you get the least barrel movement at pellet exit.

    The air does pass the pellet when it uncorks from the barrel. The best way of ensuring that this has no effect is by ensuring that the crown of the the barrel is perfectly square to the rifling. Some target airguns also have a 'still air brake' which is designed to strip away the turbulent air from the pellet."

    Just when I thought it was getting easier...........................................:rolleyes:

    Right Gents,
    Har-bloody-monics.........................
     
  7. RobF

    RobF Administrator Staff Member

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    Simple. If it groups, leave it alone. :D

    I'm not convinced that harmonics or strippers have that much effect on accuracy. I think strippers help to see the shot land, and stiffening a barrel and adding one may cut down vibrations and flip, which will relax the shooter, but that's as far as i go with them.

    But, happy to see other ideas.
     
  8. alhucoll

    alhucoll New Member

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    It works nicely with the RWS - be hard pressed to see any real improvement in the grouping.
    All the errors are now down to me to sort out!:)

    I do "enjoy" looking a bit deeper than just the point and shoot - I feel the more you understand about the influences the more relaxed you get as there are less doubts.

    Does that make sense?
    Just off to size a few more - biggest influence I've seen that makes a difference - or it could just be psychologic..................................

    Al
     

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