pcp theory

Discussion in 'General Airgun Chat' started by vinny, Jan 21, 2016.

  1. vinny

    vinny WHFTA 2015 World Champion

    Joined:
    Mar 16, 2014
    Messages:
    685
    Location:
    essex
    Club:
    M.A.D
    Say for instance ,
    a standard non regged pcp, maybe even a hft 500 :) shoots fine at 780 fps @ 170 bar , standard 8.4 gn pellet blah blah ,you now wind any restrictors out of the transfer ports ,
    would there be any advantage in lightening the spring load on the hammer back to 780 fps or
    shortening the length of hammer travel , weight of hammer etc
    please b gentle with me on this as I, m sure theres loads of combo, s ,
    ive done a bit of testing wrt this on my regged ftp without going anywhere near the reg pressures
     
    Last edited: Jan 21, 2016
  2. Conor

    Conor Never been banned from sales Staff Member

    Joined:
    May 4, 2009
    Messages:
    3,058
    Location:
    Ardboe, Co.Tyrone.
    Club:
    Back Hill Ballistics; DFTC; Nelson FTC
    You've been reading too much in the airgunforum!
     
  3. vinny

    vinny WHFTA 2015 World Champion

    Joined:
    Mar 16, 2014
    Messages:
    685
    Location:
    essex
    Club:
    M.A.D
    Conor , yes I probably have , :p but I am new to this stuff and despite trying despertely not to be a fiddler of ones eqpt (ooer), I do need to know the basics from other peoples experience, someone mentioned ISPs have 2mm hammer travel , i, m an ex engineer , i just cant resist it l
     
    Last edited: Jan 21, 2016
  4. Tench

    Tench WHFTA World Champion 2016.

    Joined:
    Sep 23, 2009
    Messages:
    1,719
    Location:
    derby
    You have picked a funny rifle to play with in the HFT500, the 400 type AA action uses pneumatic forces to close the very heavy valve as a spring just couldn't do it fast enough with that valve weight. For example putting a softer valve spring in that action reduces power because the valve head gets knocked further back into the pot quicker sealing the pot off so the res pressure fires the valve closed sooner. Most other pcp's work quite differently with a softer valve spring slowing the valve down and increasing the air delivery duration.

    Well, that is how they used to work until AA increased the pot dia to stop the valve spring rubbing brass particles off the pot which could cause a firing valve leak, presumably for reliability and financial reasons to reduce warrantee returns for valve leaks? but slowing the valve down and increasing air consumption in the process. The HFT has a massive air tube compared to the 400k yet barely beats it on shot count, having said that it still shoots very well. The BSA GS gets the same shot count from half the air volume of the HFT and from a shorter barrel.

    In general though better air flow and a shorter valve duration will make a gun shoot better and use less air with an higher bc and better accuracy, or less pellet fussy! but may increase muzzle flip due to a strong short air blast against a gentler longer one. You can go too big on the porting too, it is about finding the best balance of many variables for each particular rifle design with port length and volume playing a part too. Long ports are not good for high flow rates without having a larger dia, this creates a high volume which causes a slow pressure rise behind the pellet. it is all a compromise.

    My preference would be for the shortest lowest volume air path with nicely shaped and flowed porting with no step dia changes. Lightest smallest area valve possible, Lightest hammer with zero preload on the hammer spring when forward so the valve can close fast without having to push the hammer back against the spring. (HFT has 23mm of spring preload!!!) With a NF on top! :D

    Most valve designs are also used in fac versions so have greater area than needed which requires an heavier hammer and spring. We are using rifles with compromised designs to standardise on parts across a rifles model range, yet they will bs us with stories of it being designed for our purpose rather than the real reason of their economics. Compromised by accountants! not developed to be the best they could be!

    There is no right setup with the rest being wrong, the different design and architecture of each rifle dictates a different approach.
     
    Last edited: Jan 21, 2016
  5. vinny

    vinny WHFTA 2015 World Champion

    Joined:
    Mar 16, 2014
    Messages:
    685
    Location:
    essex
    Club:
    M.A.D
    Cheers Si ,
    I think the 23mm of preload may have caused a few premature sear deaths on slippage whilst cocking as wel
    whats an NF ?l
     
    Last edited: Jan 21, 2016
  6. simmmo

    simmmo Active Member

    Joined:
    Apr 16, 2009
    Messages:
    449
    Location:
    Buxted County HFT Republic of Sussex
    Next time you see me Vinny have a go of one of my ISPs had the hammers lightened by a third and they throw 2mm. Apparently there is no noticeable difference in lock time or shot cycle. But hey you decide. Upd the reg pressures from 95 to 105 as well apparently that shouldnt work either, but I like that sharper smaller harder hitting volume. Fluck another illconceieved idea.

    Monkey
     
    Last edited: Jan 22, 2016
  7. Tench

    Tench WHFTA World Champion 2016.

    Joined:
    Sep 23, 2009
    Messages:
    1,719
    Location:
    derby
    Sounds much like action in my rifle Andy! :) maybe not quite that short on the stroke though!
     
  8. simmmo

    simmmo Active Member

    Joined:
    Apr 16, 2009
    Messages:
    449
    Location:
    Buxted County HFT Republic of Sussex
    No Si the stroke is that short, Shaun is a magician the Anschutz trigger cassette controls the hammer stroke as well as the power screw. The smallest adjustment on the throw dramatically increases or decreases the adjustment on the power screw. But combined allows great refinement.

    Andy.
     
  9. simmmo

    simmmo Active Member

    Joined:
    Apr 16, 2009
    Messages:
    449
    Location:
    Buxted County HFT Republic of Sussex
    So Vinny you played with it shot it today out of the water what did you think? constructive critiscim?

    Monkey
     
  10. vinny

    vinny WHFTA 2015 World Champion

    Joined:
    Mar 16, 2014
    Messages:
    685
    Location:
    essex
    Club:
    M.A.D
    Dunno about critiscm mate , seemed very nice , like to have a few more shots , but seemed more like a click than a firing cycle
     
  11. simmmo

    simmmo Active Member

    Joined:
    Apr 16, 2009
    Messages:
    449
    Location:
    Buxted County HFT Republic of Sussex
    A good analogy. Anytime you want mate, Shaun knows his stuff for sure. HFT 500 barrel seems to work to.

    Andy
     
  12. Tench

    Tench WHFTA World Champion 2016.

    Joined:
    Sep 23, 2009
    Messages:
    1,719
    Location:
    derby
    Andy, I meant mine is not that short on the hammer stroke, but runs 100 bar reg and very light hammer etc like yours. I have shot one with the ultra short stroke and like Vinny says, it is too fast to call it a cycle!
     
  13. simmmo

    simmmo Active Member

    Joined:
    Apr 16, 2009
    Messages:
    449
    Location:
    Buxted County HFT Republic of Sussex
    It is quick(though apparently I can't notice) had my hammers reduced in weight from 750 grain to 500 grain so will let someone like you Simon who actually knows about engineering to decide. But I feel a difference.

    Andy
     
  14. verminator

    verminator New Member

    Joined:
    May 17, 2010
    Messages:
    93
    Location:
    London
    Club:
    Bisley
    In an unregulated gun, if you increase the transfer port diameter, you create more of a peak in the power curve.

    Once you reg it, more options become available RE the tuning of the firing cycle.
     

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