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Surprised to see power level drops when using heavier pellets!

Discussion in 'Anything Airgun Related' started by Dag, Aug 11, 2014.

  1. Dag

    Dag Pro Poster

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    For some time now I seem to have read posts that warn airgun users of the danger of going over 12ftlb if they start using a heavier pellet when they find they have chrono readings of 11.5ftlbs and above.
    Testing my .177 TX200HC tonight with 8.44gn JSB Exacts and 10.50gn Bisley Magnums I was happy to see the TX was firing the Exacts at a power level of 11.2ftlb and thinking the Magnums would therefore be at a safe level of about 11.6 or thereabouts I was surprised to see they only developed 10.1ftlb!
    As this seemed to go against all I had read I started Googling the subject and found articles which supported both viewpoints. The difference of course, which the more experienced members of this forum will know already and which I had failed to realise, is that a PCP will develop a higher power level with a heavier pellet whereas a springer develops a higher level with a lighter pellet.
    I only write this as there are probably others who have not realised this difference but who should be aware of it if their rifles are already approaching the 12ftlb mark.
    As I understand it the law will come down hard on you if your rifle is found to be capable of exceeding 12ftlbs regardless of which pellet you might happen to be using at the moment.
    Any comments from more knowledgable members as to the reasons behind this difference would be most welcome.
    Dag
     
    Last edited: Aug 11, 2014
  2. DenTB

    DenTB Donator

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    Seems really obvious , :eek: now you mention it . Very Good point, sure thats a well known fact that ,Is often overlooked,and everybody should be aware of ? Nice one . :up:
     
  3. Stevie Darling

    Stevie Darling Sexual tyrannosaurus

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    My ultra pushes more power with jsb express 14.4 than it does with as 16g, but aa pellets will push more power than accupell.

    maybe its down to pellet efficiency I don't know, but in my opinion, most sub12 rifles will go over with at least one pellet:)
     
    Last edited: Aug 11, 2014
  4. warrenater

    warrenater Donator

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    dont quote me on this but i believe as a genral rule a pcp will give more power with a heavier pellet but a springer will do the opposite .
     
  5. loki_79

    loki_79 Donator

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    Ignoring the pellet fit, which is a huge factor in the power generated (too loose = low power as air can escape around the pellet, too tight = lower power due to increased friction), the argument for pellet mass in pcp vs springer goes:

    A pcp tends to release a continuous 'slug' of air that pushes the pellet all the way down the barrel at a relatively consistent pressure, therefore heavier pellets that take longer to accelerate for a given force (f=ma) will remain in the barrel longer, allowing a greater impulse (i.e. imparting more energy). This depends on how much air is released with each shot, but it is typically more than is required (i.e. the valve may still be open even after the pellet has left the barrel).

    In contrast, a springer produces a higher pressure for a very short time, which quickly dissipates as the pellet moves down the barrel and the air compressed by the spring expands into the space behind it. For this reason, both pellets will only be accelerated for the first part of their journey down the barrel, before friction takes over and starts to slow them down. The heavier pellet reaches a lower velocity for the same applied force, and so takes longer to exit the barrel, and is therefore slowed down more by friction than the lighter one.

    As I said originally, pellet fit in the barrel has a much greater effect than mass alone, but hopefully you get the idea!
     
  6. oliver13

    oliver13 Donator

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    I've found heavy & light pellets that will go either way in springers & PCP's regardless of accepted theory, I think Loki's right & its friction in the barrel as a big factor.
    If you want to run your gun over 11ftlbs you need to check it against a lot of pellets to be sure it's not going to go over, including ultra light lead free ones.
     
  7. Steve K

    Steve K Posting Addict

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    I've said it many times before, PCP's always doing more power with a heavier pellet, and springers always doing more power with a lighter pellet is a complete myth.
    Sure some will, and some won't, pellet head size usually has much more effect on muzzle velocity than pellet weight.

    This nonsense still gets preached all over the net though :rolleyes:
     
  8. Dag

    Dag Pro Poster

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    As ever on this forum ,differing opinions but all good stuff!
    Many thanks
    Dag
     
  9. keithy

    keithy Very Active

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    Hi I shoot 15 grain pellets in all my rifles, i tried 19 grain pellets H & N barracuda extremes in both springers and PCPs, The results were springers less power, PCPs HW100 slight increase, BSA R10 .7 ft lb increase:eek: it all depends on the gun pellet combination for PCPs but springers appear to almost always drop.:)
     
  10. Akita177

    Akita177 The Absolute State of Britian podcast

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    As a basic rule of thumb light pellets should produce more power but there so many different configurations and length of barrels.
    With the TX200hc only have a 9.5" barrel depending on how its setup a heavie pellet may not get upto speed where as a light RWS hobby might reach its speed before leaving the barrel.

    There also a misconception that PCP`s have a more violent air delivery as the air is on tap so to speak, but springers have a more violent air delivery.
     
  11. timmytree

    timmytree Top Poster

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    Don't forget the softer lead pellets will often be the most efficient too, AA Fields or JSB Exacts will give higher readings than many other similar weight pellets for that reason.
     
  12. Dag

    Dag Pro Poster

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    I'm not sure how much harder the Magnums are compared to the JSB's but they certainly have a thicker skirt which may resist the rifling perhaps?
    Anyway, following the various contributions made in this thread ,particularly re pellets that may be tighter in the barrel having a lower velocity, I conducted another trial.
    This time I rolled some Magnums between two metal surfaces to give firstly a slight reduction in the head and skirt diameter, the second set to have a greater reduction in both skirt and head, and finally a set which had only the head rolled and the skirt left intact. The final set was made this way as ,although both Magnums and JSB's are 4.52 mm the Magnums definitely are harder to insert the head into the breech.
    The results of the test firing were:
    First set, slightly rolled, average 625fps ie 9.1ftlb
    Second set, increased rolling pressure, average 600fps ie 8.4ftlb.
    Third set, skirt rolled only, average 660fps ie 10.15ftlb.
    These have to be compared with the first set of untouched pellets which gave 655fps and 10.1ftlb

    Not very scientific and no great change but it does seem to show the Magnums have a head diameter which is very slightly slowing the pellets down and that the skirt diameter should be left untouched otherwise there is a drastic loss of power.
    Hope this is of some interest
    Dag
     
  13. walker

    walker Busy Member

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    very true. both my rapids dropped power when heavier pellets were put threw them
     
  14. Jfrwhite

    Jfrwhite Posting Addict

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    So the lesson here is check your rifles with a wide range of pellets, (brands, head sizes, weights etc)
     
  15. Dag

    Dag Pro Poster

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    Thinking about the results I had I realised the one practical test I should have carried out, and which I will do this afternoon, is to push the pellets down into the breech with something to reduce the initial friction when firing but without any reduction in skirt or head diameter. Back later!
    Dag
     
  16. Dag

    Dag Pro Poster

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    I put some Magnums through the TX200HC this afternoon but, as I suggested above, this time each pellet was pushed into the breech about quarter of an inch using a golf tee. The chrono readings gave an average of 664fps which equates to 10.3ftlbs.
    Not a great improvement but slightly better than the 655fps and 10.0ftlbs found originally.
    It would seem from all this that the head of the magnums is slightly larger than the head on the JSB Exacts and pushing the pellet in a little does help and is more beneficial and consistent than trying to roll pellets which proved disastrous!
    Dag

    ps I notice in earlier posts I stated the original power level was 10.1ftlb , it should have read 10.0ftlb
     
    Last edited: Aug 13, 2014

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