20mm re visited

Discussion in 'Piston & Spring' started by Nick G, Sep 29, 2018.

  1. hmangphilly

    hmangphilly Floppy Quick Phil

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    It Should be quiet .

    You'll be able to hear all your workings working
     
  2. Adam

    Adam Well-Known Member

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    Cool. Will the shroud apply tension to the barrel? Should be a very stiff setup if so; minimising harmonics and all that good stuff. :)
     
  3. Paul_T

    Paul_T Active Member

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    Nick if its not too much of a personal question... out of interest what sort of storke lenght / transfer port dimensions will you be running?

    Nice work BTW :)

    Also cheers to all that replied to my ramblings. I wont hijack this thread any longer:oops:.

    Paul
     
  4. Nick G

    Nick G Active Member

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    There will be a bush on the end of the barrel with holes to vent and to align it, this is all new so plenty of guesswork going on .
     
  5. Nick G

    Nick G Active Member

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    I am going to set it up so that i can go out to 115 mm stroke max, and add around 20mm extra spring room over the TX, this should give me plenty of wriggle room to experiment, tonight I stretched the TX to 104mm stroke , but to get it in, lost some length on the piston( hence weight) and the extra stroke coil bound the 2.7 mm wire spring i am using, so ended up with no benefit, all good fun, though. Port is 3.6 diameter x 4mm long at the moment
     
    Last edited: Oct 12, 2018
  6. Nick G

    Nick G Active Member

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    Managed to do a bit more this week

    DSCN3526.JPG DSCN3527.JPG DSCN3526.JPG DSCN3527.JPG DSCN3528.JPG
    DSCN3529.JPG
    Trigger block drilled to take a rekord , because I had one , it going to be rotating piston so will need to modify the sear. DSCN3530.JPG DSCN3528.JPG
    So comp tube and cocking lever next on the list, and I have to machine the scope vee's in , when I am fresh and feel like doing it!
     
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  7. Buffalo

    Buffalo Greyhound Gun Club

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    I honestly do not think there is any medication to help Nick. Lol
     
  8. Alanok2002

    Alanok2002 Member

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    Any more done on this nick ?
     
  9. Nick G

    Nick G Active Member

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    I have done the cocking lever, but got side tracked , will be doing some more soon
     
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  10. Nick G

    Nick G Active Member

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    Had a bit of time , so made a comp tube and a front link, pivot thingy

    1556719693395.jpg 1556719693395.jpg IMAG0090.jpg IMAG0088.jpg IMAG0089.jpg IMAG0087.jpg
    The comp tube will sit up against the breech block, and the barrel will be able to adjust back against the bottom of the trans port recess , so the pellet gets seated flush, an internal o ring seals the breech on the od of the barrel nose , so everything will lock up with no movement and no tension ( hopefully), I am making this up as I go along , next on the list is sorting the cocking linkage out ,and then a piston and rod . I have left the comp tube long as it will have a skirtless piston in as a first attempt, as the spring I have is too large for a skirted piston , and I may put some bearings fore and aft , as the last ally action I made the comp tube picked up in the action though that had an ally comp tube . Try and do some more next week .
     
    top gun phil, Tinks and hmangphilly like this.
  11. Nick G

    Nick G Active Member

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    How come the smallest parts take the longest time to make ?

    IMAG0092.jpg IMAG0093.jpg IMAG0094.jpg
     
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  12. Nick G

    Nick G Active Member

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    Finalised the cocking lever & linkage today, got the stroke I wanted , waiting for a delivery of o rings , before I can get on with the piston .

    IMAG0096.jpg IMAG0097.jpg IMAG0098.jpg
     
  13. Nick G

    Nick G Active Member

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    Made some more parts this week , and finally got it shooting ,
    Put some bearings on the comp tube , and made up a piston of sorts just to try it out, I have had some good results with 1.5mm section o ring in a 22mm lgu I did , so pushing the envelope here with 1mm section to see how it goes , very lightweight piston and a very soft spring. IMAG0102.jpg
    Piston is on the light side , also made a back venting bush for the shroud .
    IMAG0103.jpg IMAG0104.jpg
    Here is the action in one piece ,
    IMAG0105.jpg
    So started with no pre load , and 6fpe, added pre load till it stopped going up ,and ended up with 9.2 fpe and 20 mm pre load , it wouldn't make any more , so swapped the delrin top hat for a steel one , and it came up to 10.9 with 8.4 and 11.2 with 7.9, so its bouncing a bit, but at least I know it will produce the power, cocking effort is easy, so now I intend to use a longer spring with a full piston to maximise the spring room, and make it heavier so I can use less spring, it feels a bit lively at the moment , but I have no stock for it yet and its as light as a feather , so difficult to get an Idea as to what its going to be like in the end . Sorry about the Hippie brick in the last picture .
     
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  14. Nick G

    Nick G Active Member

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    Made a proper piston for it, and as I needed a bit more weight used a bronze nose and a steel skirt, but now find its 25 grm heavier which may be too much , and to get the dimensions for the spring to fit the tube I used for the skirt the spring is now smaller in diameter so stiffer , not had it in the action yet but think the piston may now be too heavy given the spring I have to use , its going to be a juggling act may have to do another piston with an ally nose.
    IMAG0109.jpg
     
  15. Nick G

    Nick G Active Member

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    Quite surprised, cut the spring down to give me 20mm of pre load , and its shooting pretty much balanced with heavy and light pellets , though the cocking arm needs a re think , as its bending, so will get that sorted , then its on to the stock.
     
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