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Air Used Per Shot

Discussion in 'Technical' started by sagalout, Jan 24, 2021.

  1. sagalout

    sagalout What a plinker!

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    Just a quick test of air used with and without an @Stevie Darling blast tamer whilst I had a rig set up for something else. I was interested so I thought some others might be as well.

    Test subject : a BSA Ultra 0.177 with Huma reg but the reg set pressure is over 130 bar and the fill pressure is 110'ish bar so the reg is just a narrow air passage, 20 shots.

    Prior to the test I fitted a Huma reg tester with a digital gauge to the air cylinder fitted with a digital gauge and checked that the plenum pressure followed the cylinder pressure.

    Shots Red10 and Blue15 clearly show what the rig was looking for initially.

    BT = Blast Tamer
    NBT = No Blast Tamer

    Pictures of the rig and the result. [EDIT] X axis is bar, Y axis is shot count [/EDIT]
    20210121_151908.jpg 20210121_151920.jpg Screenshot 2021-01-24 080655.jpg

    For the more inquisitive amongst you, here is the muzzle velocity (MV) string for the Blast Tamer string above.
    Screenshot 2021-01-24 082446.jpg
     
    Last edited: Jan 24, 2021
  2. scoie

    scoie Busy Member

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    :thumb: Certainly more efficient with it

    Blue 14 and 15 :facepalm:

    Bet it was cold down there this morning
     
  3. scoie

    scoie Busy Member

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    Blue 14 and 15 though had the same fps , so made no difference
     
  4. scoie

    scoie Busy Member

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    Got confused again :facepalm: ignore me as usual
     
  5. Squintykid

    Squintykid Busy Member

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    Erm, excuse my confusion are you doing an off-reg test?
    fill pressure 110bar
    reg pressure 130bar
    .... the gauge shows 119 bar?
     
  6. sagalout

    sagalout What a plinker!

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    You are on my ignore list! I expected you and your kids to come round and clear the drives and paths of snow for us old people :)

    I get confused to :)

    Test rig was pictured when I started and was testing from 120'ish bar down to get a feel for where MV was peaking and what the shape was. Later reduced to 110'ish bar because the higher setting meant more pellets but no more info.

    Yes, testing off reg looking for action rather than reg effects. Plenum tests done here. I intend to now repeat the current test but with the plenum gauge in place to confirm that the plenum is following the cylinder during the shot cycle.
     
  7. Autodidact

    Autodidact Thought Criminal

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    Fantastic analysis (again) from the sagalout ;) -you certainly seem to have a talent for this kind of thing fella :up::up::up:

    FWIW That's the reason I forked out for 2 x EDMUs for my Lego gun (knowing what is actually going on);)


    Be well sagalout :thumb:
     
    sagalout likes this.
  8. td_boy

    td_boy Donator

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    I'm confused... But it doesn't take much!

    The 2 graphs don't seem to correlate with regard to air used?

    What does the BT do?
    Why test so far off reg?
     
    sagalout likes this.
  9. sagalout

    sagalout What a plinker!

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    First graph is two sets of data, air used in bar, with (blue) and (red) without a blast tamer (this is two different but successive shot strings).
    Screenshot 2021-01-24 080655.jpg

    Second graph is the with blast tamer string from above (red) with the (blue) muzzle velocity (MV) string for the red air used string, showing how the air used corresponds to the fps produced at the muzzle.
    Screenshot 2021-01-24 082446.jpg

    The blast tamer is a device that reduces hammer bounce and thus conserves air. I was trying to give a graphic representation of the effect.

    If I build the gun without a reg I have now idea of how much the reg restriction may affect the shot string. The reg has very fine passage ways (0.3mm??) for the airflow and the unregged gun has no restriction between cylinder and exhaust valve.

    My previous testing of regged plenum pressure (here) shows no affective change in plenum pressure to correspond with a large variation in MV, so I am looking at the gun action rather than the reg pressure.

    By setting the reg set pressure way above running pressure the reg is not controlling the shot pressure, however the restricted airflow can/may affect the volume of air available to the shot. This chart shows the cylinder pressure in bar and the MV of the string. Note shot 10, the MV has dropped but the cylinder pressure for the shot is consistent with the other shots, then refering back to the other charts it can be seen that the volume of air used is significantly less.

    Screenshot 2021-01-24 114530.jpg

    Identifying this change in air volume used and linking it to the low MV shot is new me.
     
    cloverleaf, Blackmax and td_boy like this.
  10. td_boy

    td_boy Donator

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    Thanks for the comprehensive explanation - appreciated :thumb:
    The bit that looks odd is the first graph showing a blue line with air usage appearing to be on average about 2.3? Bar per shot - but the second graph seems to show the usage at an average 1.6? Bar.
    It also seems odd to see a rising velocity in the third graph from a fill of just 110 bar in rifle effectively without a reg.
    Something seems off to me with the blue line data.
     
    sagalout likes this.
  11. Squintykid

    Squintykid Busy Member

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    ahhh, always learning :D
     
    sagalout likes this.
  12. papisgood

    papisgood Well-Known Member

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    There ain't half some feather pluckers on ere! :)
    Thanks :thumb:
     
    sagalout likes this.
  13. sagalout

    sagalout What a plinker!

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    I am going to redo the graphs in unique colours, the blue line was just that a blue line, what it represents is shown at the side of the graph and in the explanations.

    First chart Air Usage with and without blast tamer.
    Screenshot 2021-01-24 160751.jpg
    Does that help now the blue line is green? :D

    Second chart Blast Tamer air usage against MV.
    Screenshot 2021-01-24 082446.jpg

    Third chart Blast tamer cylinder pressure against MV.

    Screenshot 2021-01-24 161119.jpg

    That's because the reg is fitted, the port is enlarged and flowed, the hammer spring is altered, the EV spring preload altered and the EV restrictor is in the bin.

    Here's 0.177 Ultra, unregged with an altered hammer spring and port but still with a port restrictor, this blue line is not the same as any blue line you might have seen above. Not the fill pressure is 135 bar to 65 bar.
    data01.jpg
     
    _foxbat_ and Autodidact like this.
  14. BallisticBill

    BallisticBill Too much keyboard, not enough action!

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    It would be interesting to see how the NBT air usage and MV compare (the NBT equivalent of graph 2). You've established the BT is saving air but is it introducing additional MV variation? I'm not expecting it. If air efficiency and MV variation improve you have a winner... otherwise there's a trade off.
     
    sagalout likes this.
  15. jesim1

    jesim1 Kit bitch to the Stars

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    I know you have put a lot of effort into this as I do a few of these kind of tests also with pellets/guns/chronos, but for a regged Ultra to be doing 30fps spread over 20 shots is not something I could live with, I'm getting under 10fps spread across 100 shots on some of my guns. To me this is going to mess with your data no end and make it extremely likely it's unreliable :oops:
     
    sagalout likes this.
  16. td_boy

    td_boy Donator

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    If a reg is fitted then it doesn't appear to be working in graphs 2 & 3.
    But then I thought that was what you were trying to emulate by running a cylinder pressure lower than the reg set pressure.
     
    sagalout likes this.
  17. sagalout

    sagalout What a plinker!

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    I will run that test Bill, but I will have to run BT and NBT again because I have changed some of the internals.


    It's not runnng on reg, the reg set pressure is 130 bar plus, the fill pressure is 100 bar. I am looking at the performance of the gun action.

    It's not shutting if that's what you mean, and therefore I am able to see the effects of the action tuned for a reg, affected by the reg air flow but not actually regulated.

    It is affecting the amount of air that can flow from the cylinder to the pellet during the exhaust valve (EV) open time. If I ran the gun without the reg in place the EV is directly connected to the cylinder and the resultant strings would be different.

    I have made a wild assumption that the restricted airflow of the reg affects the EV dwell and possibly lift.
     
    BallisticBill likes this.
  18. BallisticBill

    BallisticBill Too much keyboard, not enough action!

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    I know what you're doing. :thumb:
     
    cloverleaf and sagalout like this.
  19. sagalout

    sagalout What a plinker!

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    Out of interest, is that with unweighed and unsorted pellets?

    I shot this full string (on reg :D) with pellets straight from the tin a fortnight ago but it is not and everyday occurrence and @BallisticBill will be along shortly to point out that it's actual spread is more like 16fps because of the FX chrono granularity :D.

    Sheet10.jpg
     
  20. td_boy

    td_boy Donator

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    Wouldn't have just running the gun in regulated mode over a set number of shots and subtracting the remaining air in cylinder, then divided by the number of shots to determine the per shot usage - given the same answer rather more simply?
     
    sagalout likes this.

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