Head size - WOW

Discussion in 'General Airgun Chat' started by CameronWilson, Mar 2, 2013.

  1. CameronWilson

    CameronWilson Member

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    I've never really paid a great deal of attention to pellet head size or batch number in the past. However this morning, I thought I would carry out a little experiment with the pellets I have on hand, to see if there was a particular batch which performed markedly better.

    I was shocked to learn:

    JSB Exact Express
    4.51 (30005810) = 820fps
    4.52 (6004909) = 800fps

    That's the difference between 11.2ftlbs and 11.8ftlbs, for two pellets that are the same design and weight.

    Quite an eye-opener...
     
  2. Charlts

    Charlts Getting dusty

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    You didn't think the rest of us did that just because we like numbers did you:D, welcome to the club, now you'll end up only shooting a particular die or batch number and even then checking everything!!:D

    You're doomed now!
     
  3. CameronWilson

    CameronWilson Member

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    :D

    I'm genuinely surprised at just how much of a difference it makes.*

    It was a comment that a fellow shooter made last week, that got me thinking. He had found that a 4.53 head size took less wind, and he believed that this was down to the barrel gripping the larger head size tighter and imparting a greater spin on the pellet.

    I'm starting to think that it's not the larger head size that takes less wind, but rather finding the perfect match between the barrel and the pellet? Would the physics suggest that a pellet travelling 20fps faster would take less wind anyway?

    So what's the lesson to be learned? That you select the head size that comes out of your particular barrel the fastest, because that's the most efficient?

    What do you guys think?

    Cam.







    *But a little more practice would probably make a bigger difference to my scores...
     
  4. Gar73

    Gar73 Douchebag/Mook Identifier

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    Don't go any deeper you will fry your brain. Don't even look at the" magnus effect".
     
  5. CameronWilson

    CameronWilson Member

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    OK.

    Now I have to look at it!

    :)
     
  6. NJR 100

    NJR 100 Because I`m AWESIME !!

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    4.51, 4.52, 4.53 = Mytholagy

    Try a few from a tin and see what the real head size is.

    What your finding is a die + batch number that suits your barrel.
     
  7. CameronWilson

    CameronWilson Member

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    Thanks for all the replies, Guys!

    How do I know when I've found a good die + batch?

    • fastest out the barrel?
    • most consistent over the chrono?
    • tightest group sizes?
    • all of the above?

    Or do some of those criteria above really make no difference at all?

    Thanks again,

    Cam.
     
  8. neilL

    neilL New Member

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    • They all land where you aimed to make them land (at 55yds).

    Perhaps not necessarily where you should have aimed though :D So, a reasonable group without mind breaking flyers.
     
  9. RobF

    RobF Administrator Staff Member

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    Agreed. Most jsb pellets will fall into a 4.50 hole.
     
  10. Ratinator

    Ratinator Well-Known Member

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    less wind dry

    I have recently stopped using lube,and i think the pellet's are takeing less wind straight from the tin.
    Has for head size i've found that if you size a pellet down,it reduces the fps not increases.
    I also think that 11.2fp is fine, i run my express pellet's at about 805-810 no need to run thing's flat out.
     
  11. CameronWilson

    CameronWilson Member

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    Just back from testing all the different pellets that I have on hand, and there's no doubt that the Expresses group far tighter than everything else.

    They're also very consistent through the chromo.

    I guess it would make sense to take the 820fps 4.51s, and bring the power down so that they're running at 800fps like the 4.52s – surely a more efficient and 'calm' rifle?

    Cam.
     
  12. LANKY MK

    LANKY MK this **** is killing me.

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    Chris Cundey bought some pellet sizers from ukNeil, we spent afew hours playing on the range & found the smaller we sized them the faster they went over the crono.

    Ps: if my failing memory recalls correctly.

    Mark
     
  13. Ratinator

    Ratinator Well-Known Member

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    not for me

    I found that sized pellets through my ev and walther drop about 10fps of normal.
    My thaught's were that air was escaping round the skirt before it flaired out to fill the barrel.
     
  14. LANKY MK

    LANKY MK this **** is killing me.

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    That's what we expected, if memory recalls.

    It was Chris's steyr we crono'ed

    Mark
     
  15. Charlts

    Charlts Getting dusty

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    There's your problem then mate, reg was probably on the way out!:D
     
  16. Conor

    Conor Never been banned from sales Staff Member

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    I tried sizing down my pellets once and my group sizes all decreased...I'll get my coat!
     
  17. fireblade

    fireblade Team AirArms

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    If you size a pellet down and it loses speed, it is because there is energy lost by the expansion of the pellets tail to fit the rifling, which also means you have a slightly larger barrel than the sizer ( a pellet sizer only sizes down).

    To find your head size.....

    E.G.

    If you try,

    4.52's and you get 785fps, then you try 4.53's and the speed drops by 5 or more fps then its too tight so get rid, if it stays at 785 or higher thats the size to use.

    If you try,

    4.52's and you get 785fps, then you try 4.51's and they are 5fps or more slower, use the 4.52's, if they are faster by 5fps or more then use the 4.51's.

    this will only find you your best fit, it doesn't find you the best batch for grouping, that you will have to find yourself with testing.

    Welcome to the Mind F***, :eek:o that is pellet selection :D
     
  18. fireblade

    fireblade Team AirArms

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    P.S pellet sizing hardly ever works, just as conor says the grouping opens up.
     
  19. Delphinus

    Delphinus New Member

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    It's like Simon wrote.

    The size in label doesn t mean nothing I also recommend to measure the head but what it s important is how a pellet group.

    Recently I bought 4.50/1/2/3 the biggest head was the 4.50 with 4.486 the smallest head was the 4.53 with 4.45
     

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