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"The Sweet Spot" how much real difference?

Discussion in 'Anything Airgun Related' started by dynarod, Sep 13, 2014.

  1. dynarod

    dynarod Engaging Member

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    Location:
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    I own a few regulated and unregulated rifles. you hear all the time about people filling their guns to the sweet spot. i was just
    wondering how much "actual" difference the sweet spot makes to the poi? i was going to do a test where i fill a unregulated rifle ie s410f
    to 190 and just keep shooting the same target all the way through the curve with the same aim point so i can see how much in real
    terms it makes. as i'm not down my perm for a few days i wondered if anyone has tried this? i think it would be very interesting.
    Maybe do the same with a regulated rifle to see the difference...
    If no one has i'll post the results in a few days.
     
    Last edited: Sep 13, 2014
  2. landymick

    landymick Very Active

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    It is always handy to know,filling higher is just a waste of air.When you find yours you will be ready with the first shot & not guessing that its on.
     
  3. whitevanman574

    whitevanman574 bell target champion

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    makes all the difference
     
  4. dave goodall

    dave goodall Donator

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    It can make a hell of a diffrence
     
  5. themadspread

    themadspread Donator

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    when i first got my aa s 400 first filled it to 190 and first 20 shots were crap but when it gets to 170 ish its like shooting a different gun the sweet spot makes a big difference
     
  6. tomsteebs

    tomsteebs Donator

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    It would be the same as using a inconsistent rifle next to a consistent one. When you have the choice off which to use, the consistent one is a obvious choice.

    Atb
    Tom
     
  7. dynarod

    dynarod Engaging Member

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    So no one has actually done it then.. i know what difference it makes and
    i normally fill my s410 to 170. but i was just wondered what it actually looks like on a target.
    I'll do it tomorrow just out of interest.
     
  8. tomsteebs

    tomsteebs Donator

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    If you see my "defiant pellet test" thread I made last week you will see the grouping gradually drop over the fill slightly (this was all done in the sweet spot)

    And poi at 25yard in .22 I found to change from the full fill to sweet spot. By about 1/2"-1" lower at peak charge
     
    Last edited: Sep 13, 2014
  9. cloverleaf

    cloverleaf Honorary Member

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    I define the "sweet spot" of my unregged rifles based on a 1.5% velocity spread from max - i.e. the lower cutoff point a rifle producing 800ft/s at the peak of its velocity curve / sweet spot would be 788ft/s.

    The table below contains what Chairgun says about a rifle firing 8.44gn JSB exacts at velocities of 785ft/s and 774ft/s (1.5% less than max. velocity), plus 746ft/s (5% less than max. velocity). 785-774ft/s would represent the boundaries of my "sweet spot", 746ft/s is well outside this, and could easily be encountered if over filling a rifle or running it too low on air.

    [TABLE="width: 800"]
    [TR]
    [TD="align: center"]Muzzle Velocity, ft/s
    [/TD]
    [TD="align: center"]Velocity, % of Max[/TD]
    [TD="align: center"]Muzzle Energy, ftlb
    [/TD]
    [TD="align: center"]Fall of Shot @ 35yd, mm
    [/TD]
    [TD="align: center"]Delta FOS from min @ 35yd, mm[/TD]
    [TD="align: center"]Fall of Shot @ 50yd, mm[/TD]
    [TD="align: center"]Delta FOS from min @ 55yd, mm[/TD]
    [/TR]
    [TR]
    [TD="align: center"]785[/TD]
    [TD="align: center"]100.0[/TD]
    [TD="align: center"]11.55[/TD]
    [TD="align: center"]106[/TD]
    [TD="align: center"]-[/TD]
    [TD="align: center"]231[/TD]
    [TD="align: center"]-[/TD]
    [/TR]
    [TR]
    [TD="align: center"]774[/TD]
    [TD="align: center"]98.5[/TD]
    [TD="align: center"]11.23[/TD]
    [TD="align: center"]108[/TD]
    [TD="align: center"]2[/TD]
    [TD="align: center"]238[/TD]
    [TD="align: center"]7[/TD]
    [/TR]
    [TR]
    [TD="align: center"]746[/TD]
    [TD="align: center"]95.0[/TD]
    [TD="align: center"]10.47[/TD]
    [TD="align: center"]115[/TD]
    [TD="align: center"]9[/TD]
    [TD="align: center"]257[/TD]
    [TD="align: center"]26[/TD]
    [/TR]
    [/TABLE]


    In a nutshell, staying inside a 1.5% velocity sweet spot gives a max vertical POI variation of 2mm at 35yd and 7mm at 50yd. Dropping the velocity by 5% from its maximum gives a total POI variation of 9mm at 35yd and 26mm at 50yd; which is pretty substantial IMO.

    A well-setup S400 series rifle might have a 1.5% sweet spot at pressures between 190 and 120bar; however a poorly setup gun might only give acceptable shots between 150 and 95bar - making overfilling / running the rifle outside its optimum pressure envelope far more likely.

    I'd certainly be interested to see some real-world results if you do get down to some testing - corresponding velocity results would be good too ;)
     
  10. dynarod

    dynarod Engaging Member

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    Well i finally got round to doing abit of testing. it didn't really prove alot apart from i've got the weirdest bsa ultra going. i thought i would use my ultra as i thought it would
    have a bigger power curve than my air arms. here's the results. there was a slight breeze coming from the right but i just aimed in the center.
    View attachment 103967

    I doubled loaded a pellet hence the low 1... heres the pellet velocity shot string data from a full 200bar fill.

    594, 590, 591, 590, 590, 589, 585, 589, 590, 585, 584, 589, 446(dl), 587, 589, 586, 584, 581, 585, 589, 582, 579, 584, 580, 579, 576,574, 572......551

    It would appear my ultra doesn't have a power curve as such. more like a power slope!! and it's only good for 28 shots from a full fill. strange gun.
    think i might need to get it regged just to increase the shot count. it's very accurate in the zone though.

    Think i might need to do this test again using my s410f to see if thats any difference.
     
    Last edited: Sep 22, 2014
  11. themadspread

    themadspread Donator

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    the 410 will stay in the sweet spot way longer
     

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