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Calling all pcp techno's!

Discussion in 'Anything Airgun Related' started by Igotknobblies, Feb 21, 2014.

  1. Igotknobblies

    Igotknobblies Engaging Member

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    Hi. I'm new to this site having registered expressly to seek advice. I secured a Webley fx2000 in .22 second hand with lots of extras.. 15L tank, hard and softcases, silencer and 2 scopes (1 u/s). Apparently serviced recently by a reputable gunshop. Over the chrono, bisley superfield coming out at 11.3'lb but Bisley Magnum at fractionally over the limit. I have reduced hammer spring pre tension and it is now 'legal'. I then charged to 200 bar and fired a shot string of 80 shots down to 100 bar. Interesting results, nothing like expected. I'll try to attach a pic of my graph. Certainly a pattern but with a quality pellet, surprised to see such a fluctuation in speed. Best spread between 170 and 140 bar with spread between 616 and 622fps. Question is, with a result like this, should I consider a full valve strip down? Once that is done, there are 2 adjustments with stock transfer port: ie the knock-open valve restrictor and hammer. The latter can be altered by its weight, its spring and spring pre-load. How should I flatten the shot string curve without firing many hundreds of pellets to see I've made adjustments in the wrong direction? Pic to follow. Cheers! IGK
     
  2. Igotknobblies

    Igotknobblies Engaging Member

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  3. spike589715

    spike589715 Busy Member

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    Hi
    for an un regulated gun this is the sort of curve you will be getting ..... You may get better shot to shot consistency by stripping the gun cleaning and re lubricating ... This will help the valve to get the same "hit" every time - but as the pressure changes in the chamber the response from the valve will also change hence the curve -Pellets can very as well in weight which will effect the shot to shot consistency
    in practice this will probably not make a massive difference in point of impact of the pellet - depends how important this really is
    most guns are un regulated and have a curve ...

    http://www.theywalkamongstus.co.uk/airguns/at44.html

    this shows the graph from my new AT 44 as it came from the shop - I fitted a regulator and the graph is further down the page ... I am a fan of regulators

    hope this is of some help
    simon
     
  4. genisis22

    genisis22 Engaging Member

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    hi been in similar position, when adjustments made, start at say 100bar fill fire 3/4 shots over crony then fill to say 120, 3/4 shots then fill to 150 etc ect this will show power and consistancy across fill, wait say 15 mins after filling to allow things to cool and try to do test at same ambient temp,this will sort out sweet spot,
     
  5. terry1001

    terry1001 Major Poster

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    Since pellet weight can vary quite a bit even in top quality products you can't rely solely on the velocity readings. Some variation is inevitable in actual velocity and probably also in the chrono itself. For most people the important part is whether or not the point of impact varies.
    Using the chrono for a couple of strings from full down to 100 bar will show you the range of pressures which give the most consistent results - this is normally well below the max fill pressure and down to maybe 110/130 bar depending on a lot of variables. When you have established this you know the pressure to fill to and also how many shots you will get before needing to refill.
    Making adjustments requires a lot of time and effort as you should only make one (small) change at a time and then check the effect. You can save air by reducing the volume of your cylinder by putting a perfectly clean, inert packing into it.
    Fitting a regulator is a simple process, getting the rifle tuned to get the best out of it is not a simple process and can take a considerable time to achieve. I suggest having a look at the videos on youtube from Robert Lane Design which will explain a lot of the process.
    Unfortunately tinkering can become addictive - maybe having anti tamper fitted is a way to save us time and money :laugh:
     
  6. bunnyblatter

    bunnyblatter Pro Poster

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    It sounds as though you understand the workings of your rifle mate. I'd try the basics first with the strip and clean and try it after that. But like has been said there will be a power curve in an un regged gun
     
  7. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    [​IMG]

    That certainly is a bit crap for an FX2000 :(

    A few Q's...

    - What pellet is that velocity graph for? At the peak velocity of 624(?)ft/s, a 15.9gn RWS Superfield will be producing around 13.75ftlb, a 21.4gn Bisley Magnum will be producing 18.5ftlb. Either way far too hot!

    - Is the gun a carbine or full length?

    - You say you adjusted the striker spring pretension - how did you achieve this? AFAIK there's no facility to do this on the FX2000; if you stuck a punch through the side to lock the assy while twiddling the rear of the striker through the open rear end with a screwdriver, you've actually altered the striker stroke (which is a perfectly valid way of reducing the energy)

    - Do you know where the transfer port restrictor is set?



    A few thoughts:

    - Your graph shows a) a very pronounced energy curve, b) very few acceptable shots per charge and c) a large velocity spread.

    - By way of comparison (from the limited testing I've done so far) my full length .22 RWS Excalibre (practically the same gun as the FX2000) gives maybe 70-80 shots with a very flat curve from around 200bar down to about 120, with an extreme spread of maybe 10ft/s and a shot to shot consistency of around 6ft/s.

    - The shape and poor shot count of your graph could be the result of excessive muzzle energy or a wide open transfer port and very little striker stroke.

    - The inconsistency may be due to a dodgy breech seal or more likely lots of grease in the striker assy if it's just been "serviced" :rolleyes: In addition the striker head can become loose on the shaft (these are the two bits you screw together or apart to lengthen or shorten the striker's stroke) as the method of securing it's a bit crap and unless thread lock is used they can move..


    HTH - more information might be useful to help nailing down the cause of the poor performance ;)
     
  8. Igotknobblies

    Igotknobblies Engaging Member

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    Thanks Cloverleaf. Yes, rather crap! Bisley superfield. Yes a bit hot in centre of power curve. Set striker to below 11ftlb at 200 bar not realising it was likely to go over. Is there a link to any full strip down videoas only got as far as striker. I know about valve restriction screw and lock screw on top. If I were to carefully screw down to its seat, approx how many turns should I take it out to attain factory spec for sub12ftlb? Once done it should just be striker distance and spring weight. It could have after market spring on but at least that should give consistent results. . I think I should replace the breech sealing o ring. How is this done? My fx is full length. You mentioned the striker adjustment being loose. Mine was until I used plumbers ptfe tape to lock it up but retain adjustability.To be honest a full strip and Inspection needed before final adjustments. Cheers, IGK
     
  9. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    PM sent ;)
     
  10. Akita177

    Akita177 The Absolute State of Britian podcast

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    When you strip the gun look for signs that if the transfer port may have been drilled or modded measure the diameter of the hole and check that is the correct size for a standard FX2000.
    probly not the case but worth a check on old guns as some numptys butcher them to try and get more power out of the gun.
     
  11. Accuspell

    Accuspell Pro Poster

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    Whenever you set the power on your rifle, use a fill pressure of 150 bar, or at least use the 150bar part of the graph as this is where all rifles will make their peak power, regged or unregged this pressure gives the most realistic reading. More importantly, it is the pressure the Police (or their contractor) will use to determine the velocity of the rifle.

    At 200bar the rifle will make LESS power because the hammer has to overcome the greater pressure keeping the valve closed. As the pressure behind the valve eases, so the power increases, until it gets to the best balanced state, then the pressure drops off the other side until it gets to the point where there is only a phut of air leftand power drops off.
     
  12. Igotknobblies

    Igotknobblies Engaging Member

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    s137
     
    Last edited: Feb 22, 2014

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