1. The Forum Rules have undergone some minor changes and updates.  Please take the time to read them; it will only take a couple of minutes of your time. By doing so, you lessen the chance of incurring the wrath of the moderation team or making yourself look foolish to other members.

    90% of users posting adverts in the Sales forums need to be reminded to read the rules as their posts are wrong.  This is unnecessarily time-consuming and will no longer happen - if your advert doesn't follow the Sales Rules it will be deleted and you'll have to start all over again.

    To close this box once you've read it (and the Rules), click on the X in the top right-hand corner.

    Thank you.

    AGF Staff



    Dismiss Notice
  2. A reminder of one of the Forum Rules:

    'Behaviour

    Do not make inappropriate or offensive posts - including threats, harassment, swearing, prejudice, defamation, deliberate insults or name-calling, other negative remarks about this forum, its moderators and administrators or your fellow members. Even if this is just your own personal opinion, RESPECT YOUR FELLOW MEMBERS.'

    There have been changes made to our censoring software in an attempt to help with this growing problem.

    Click the X in the top-right-hand corner to dismiss this notice.
    Dismiss Notice
  3. Dear members,

    Our membership (like our country) consists of people from all walks of life; different in far more ways than can be listed here and each with a different view based on their experience of life - regardless of their colour, religion or cultural heritage. Every single person in the UK has been born of mixed race – we are a multi-coloured and multi-cultural country.

    As many of you are aware there are a handful of individuals amongst this membership that persist in making provocative, inflammatory, racist and otherwise offensive comments. This has been happening across the forum to a certain degree but is most especially prevalent in the Adult section.

    The moderation team has tried to stay on top of this, however unfortunately because of the ‘offensive’ nature of much of its content we don’t monitor the Adult section quite as much as perhaps we should. As a result much of this behaviour has gone unnoticed unless it has been reported to us. While the team always intended to take a "light touch" approach to the Adult section it would seem that some people aren’t quite adult enough to be left unmonitored after all.

    This behaviour is, and always has been against Forum Rules as well as the specific stipulations of the Adults forum and it will no longer be tolerated. We feel it's time to draw a line in the sand and as such from this point onward offenders will receive an immediate and permanent ban from the forum.

    In order for us to achieve our goal of restoring the forum to the friendly and tolerant place it once was, we ask that ALL members be mindful of the content they post and help us to stop unacceptable behaviour by using the 'Report' tool at the bottom of any offending post - the results of which can be seen only by Admin/Moderators.

    You should all receive a copy of this message by PM. 

    To close this message box, click on the 'X' in the top-right-hand corner.

    Dismiss Notice
  4. Hotmail block emails from us entering your inbox. Unless you can setup a safe sender you will not get activation emails from the forum. Please use an alternative provider or complain to Hotmail.
    Hotmail addresses include.

    @Hotmail.co.uk @Hotmail.com @outlook.com @Live.com
    Dismiss Notice
  5. Postings on Politics, Religion & Controversial Off-Topic Material

    The majority of users do not want to read about these subjects and people have left the forum as a result of it – this is after all an 'Airgun' Forum. It’s all very well to say they don’t have to read it if they don't want to, but as most of us use the ‘New Posts’ button there is no easy way to avoid it.

    All AGF staff members are in favour of people being able to discuss what they want, but we have to draw the line somewhere if it is upsetting other users. We don’t want to read about these topics either.

    IMPORTANT- The discussion of politics and religion is no longer allowed anywhere on the forum (including the Adult section).  The only exception is if it's airgun related - they must be put in the Airgun Related Politics section..

    We will not tolerate bullying or personal attacks, racism or any other offensive 'isms'. we will remove these topics from the forum, we will not give you an area where you can abuse each other. We will not hesitate to ban offenders.

    To clear this text box, click on the 'X' in the top right-hand corner.

    Dismiss Notice

Question One for the technical boffins...regards pellet acceleration and pressures etc

Discussion in 'Anything Airgun Related' started by bigtoe, May 31, 2015.

  1. bigtoe

    bigtoe Donator

    Messages:
    910
    Likes Received:
    55
    Location:
    Stockport
    So...as you shoot a springer, the pellet starts to move, the void it leaves behind it is growing continually till the pellet exits the barrel. This void is where the peak maximum pressure created by the piston leaks into...so the pressure in the compression cylinder is dropping as the air is expanding and the pellet is accelerating.

    So....the void grows faster with the bigger calibres...1mm of movement for a .22 pellet adds 0.024cc of airspace, a .177 has 0.016cc , this space is what makes a .22 shoot nicer than a .177 as the piston comes to rest softer with less bounce and surge...however:
    A .177 pellet accelerates faster, there is less surface area on a .177 to create frictional losses...so the question.

    Given that a .177 pellet is accelerating faster than a .22 pellet, is the void growth proportional if we set the final velocity 50% higher for the .177, as at 1.5mm moved the void would be 0.024cc, the same as 1mm of movement for a .22 pellet?

    Im thinking for example, a 16gr pellet .22 travelling at 565fps = 11.34fpe
    An 8gr .177 travelling 50% faster would be 847.5fps = 12.76fpe

    The .177 set up is just theory obviously ;), im thinking could there be a magic ratio where the shot cycle would match the .22's?

    What we need to know is how much faster would an 8gr pellet need to be travelling to allow the same rate of pressure drop within the compression tube...bit complicated as frictional losses come into play etc...but its worth thinking about.

    Something else to consider...if a .177 rifle is set up to deliver 600fps with a 7gr pellet, and then the barrel is swapped for a .22 of identical length and preload is adjusted to deliver 600fps with a 14gr pellet...which set up would be the most efficient?

    If anyone happens to be good with excel and can get this down in a spread sheet so life becomes easy..pass it my way ;)
     
  2. themadspread

    themadspread Donator

    Messages:
    10,855
    Likes Received:
    4,295
    Location:
    oxford
    you need ballistic boy to answer that one he,s well clued up on this sort of thing
     
  3. bigtoe

    bigtoe Donator

    Messages:
    910
    Likes Received:
    55
    Location:
    Stockport
    I bet he is on with it...however it was more a post to get a few peoples minds going.

    To have a go at answering my own last question, i think the .177 would be more efficient than the .22 doing the same FPS (note not the same energy ;) )
     
  4. loki_79

    loki_79 Donator

    Messages:
    279
    Likes Received:
    50
    Location:
    Oxford
    I'm currently writing a program to simulate a springer from first principles, so that will certainly give you a good idea of the (theoretical) answer to this. I just need a few more days to sort out the user interface, but most of the physics is working nicely.
     
  5. AlsoFishes

    AlsoFishes Well-Known Member

    Messages:
    93
    Likes Received:
    0
    Location:
    Horta
    Here's a test for people:
    Give two reasons why a diabolo pellet still accelerates briefly after leaving the barrel!
     
  6. Ballisticboy

    Ballisticboy Busy Member

    Messages:
    919
    Likes Received:
    351
    Location:
    Maidstone
    My initial thoughts without any modelling are that what you are after is for the rate of change of barrel volume to be the same for both calibres. This means that, as you say, the rate of change of the .177 pellet travel needs to be 1.5 times that of the .22 pellet travel at all times which is complicated by the different rates of acceleration needed. (1.5 times I think probably but don't quote me on that) The problem is that the .177 pellet weighs about half the weight of a .22 pellet so the pressures needed for the two cases are not the same so the gun internals would be different which will affect the gun feel. I also think the friction will probably spoil everything as lead has quite a high coefficient of friction with steel.
    Luckily my knowledge is in external ballistics, not internal ballistics, so that is my excuse if I am completely wrong.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice