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Playing About With A Prosport.

Discussion in 'Technical' started by squib, Jul 11, 2019.

  1. squib

    squib Busy Member

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    I picked up a .177 prosport recently, firstly as it was at reasonable money, and secondly as I don’t own a springer in .177 anymore.

    It shot quite well, and was low 11 ft/lbs on the chrono, but it was dieseling a fair bit. Pulled it apart and the standard innards were packed with grease.

    Cleaned it all off, and relubed sparingly with STP/graphite. The twang was unbelievable, it was like something from the fairground. :facepalm:

    Next job, I replaced the guide and top hat with Delrin. The twang although reduced was still too much for me.

    I then took a slightly different tack. I’d had good results lightening the piston on my 95, and have had an interest in the TL conversion. I figured if I ballsed it up in such a monumental fashion, I could always get the TL conversion done.

    After about 2 minutes of internet research I arrived at a TP size of 3.9/4mm, and a piston weight of about 150g.

    I put the piston in the mill vice, and set about it with a 12mm cutter. I got it down to about 175g from memory, again from memory the starting weight was 225g.

    This is the piston post milling, 4 x 12mm slots running most of the length:

    3C34F8F5-2B5B-4CCB-AE2D-49B19622E3D1.jpeg


    Put it all back together, and although the shot cycle has sped up with the lighter piston, I was back to square 1 with the twang. I think there was two reasons, firstly the spring is really snug in the piston - I couldn’t even get a Guinness can sleeve in there without it binding. Secondly, I’d removed too much material from the piston wall, the 4 ‘bars’ that now connected the front and rear of the piston were quite thin and flexible, and I think these may have been making a racket as the piston came to a rest, a bit of a resonance thing perhaps.

    The next stage was to get a bit more drastic. I cut the bulk of the piston walls away with a disc cutter, and then cleaned up in the lathe. Also, the front Delrin bearing wasn’t a particularly good fit in the cylinder ( cylinder ID 25.1 / bearing 24.7 ) so I ditched the Delrin, widened the slot a touch, and put in two o rings that formed a good fit into the cylinder without increasing friction.

    This is the first version with it now skirtless, with the new orings, and my quick and dirty top hat and slip washer.

    97FA7FD3-3DA1-4CD4-B40B-29A3804573E6.jpeg

    Put it back together, and it shot beautifully. Very little recoil, and not a hint of twang, very quiet. But, it was only giving me 10j.

    Next step was to try the same amount of preload, but add a bit of weight, so I fitted the original top hat with my Delrin washer. Incedentally, I had built a new guide with 5mm of preload into the guide, and this also serves to strengthen the guide at the back end.

    47ECCF99-CBD4-49E0-927F-4FE7C54D8525.jpeg

    5C991EA7-2D4D-4319-B88E-9BEB4993190D.jpeg


    This gave me very similar to the previous version, but only gave me 12.5j, but shot very nicely.

    The next attempt was a bit of a chance it, so I just whacked up the preload by putting in both top hats. This was never intended to be the finished job, I just wanted to see what the additional preload did. As it happened it wasn’t such a great idea, as when I cocked it out of the stock to test fire, the safety didn’t engage, so loading it was fun :eek:
    This gave me about 14j.

    3C130C8A-5411-4576-8BC7-54DF75AEE01D.jpeg


    For obvious reasons I didn’t spend much time testing this configuration, but concluded the additional preload was worth it, but didn’t want anymore, and would need to increase weight a touch if I wanted more FPS. With that in mind I turned up a fresh ( heavier ) top hat from stainless, and trimmed a few mm off the spring guide to address the safety latching issue.
    Before I finally reassembled the gun I made extra sure the safety was latching by cocking minus the spring.

    This is the same piston with the longer top hat, guide and spring.

    B7F16D3F-A72E-4281-BD43-5A80BC5274B8.jpeg


    This configuration was a touch hot nudging 17j. Being too pretty for prison I had it apart again, and trimmed the top hat down by 4mm.
    This is now giving me 15.5j ( 11.4 ftlb). I suspect this will creep up once things bed in, so will keep an eye on it, and it’s a quick job to trim the top hat. I may even replace some of the top hat length ( and mass ) with Delrin washers to see the difference with less weight / same preload.

    This is how I ended up this evening, which I didn’t think was to bad after 20 shots and an evening of major surgery.


    F1E05386-092E-4384-996C-C1363F658F90.jpeg
     
  2. Deejayuu

    Deejayuu Donator

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    Great job/read. Thanks for sharing. The AA do tend to twang/boing in my limited experience.
    I just go for sleeving piston/guide as fit 'cos can't do what you do.
     
    squib likes this.
  3. Gary Jones

    Gary Jones Post Whore

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    Some next level tinkering that mate. Looks a good job. :up:
     
    Tyler durdon and squib like this.
  4. squib

    squib Busy Member

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    If you read the ongoing 22mm conversation thread and see what those lot are discussing, this isn’t even Sunday league stuff :confused:
    But thanks :thumb:
     
    Gary Jones likes this.
  5. Al Stevens

    Al Stevens Well-Known Member

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    How much preload has it got now?
    What's the cocking effort?
     
  6. squib

    squib Busy Member

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    There’s an additional 1-2mm at the trigger end, and I’d estimate an additional 12mm at the piston due to the longer top hat.
    Cocking- I can’t say it’s greatly different from when I got it. I didn’t take much notice tbh, there was nothing unusual about cocking it.
     
  7. Tyler durdon

    Tyler durdon Post Whore

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    Great skills you got buddy !
     
    squib likes this.
  8. Peter Collins

    Peter Collins Engaging Member

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    Fantastic read, I am not a man into my springers too much but I found this really interesting and well written. Many thanks!

    Pete
     
    squib likes this.
  9. Wofty

    Wofty Heinz Meanz Springz

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    'Too pretty for prison':laff::laff:
    Top work!
     
  10. Nickg

    Nickg Busy Member

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    I would lose the o rings as the friction they are creating is where you are losing your power , make a good delrin bearing instead , your twang is probably the fit in the bore of your top hat , most people over look this . Standard tx pistons can come down to 180 grams just by reducing the diameter and losing some material from around the rear bearing .
     
    Gazza600 likes this.
  11. squib

    squib Busy Member

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    The twang went with the the piston skirt :thumb:

    Regarding the orings/Delrin, I had considered that myself. I may even remake the top hat to incorporate another Delrin bearing so there’s 2. Although it’s quiet enough, and shoots and cocks well enough, I wonder if keeping the piston more true in the cylinder would improve things further.

    Thanks for the pointer :)
     
  12. telephonepete

    telephonepete Donator

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    Great read. I have a spare mark 3 piston and a very talented nephew. I may let him loose on something like this. Let him read up and then just go for it. Play around with it as it were. Thanks for the idea.
     
  13. Al Stevens

    Al Stevens Well-Known Member

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    Go for it!,try and get creative/inventive,nothing to lose if its a spare,,good fun,you will probably get hooked:)
     
  14. Nickg

    Nickg Busy Member

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    A very good first tune , is to lighten the piston as above , then machine the dovetail off , make an ally nose up with a 10mm thread to take either an hw seal or my preference is an o ring , 200g and 82mm stroke work well .
     
  15. rabbitist

    rabbitist Donator

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    Prosports are in my opinion the greatest rifles ever made with a little tinkering
     
  16. Bozz

    Bozz Engaging Member

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    Hi nice job there maybe you should setup building and selling them I'm sure there must be a market as not everyone has the skill / tools to do such job. Well done all the best Graham
     
    squib likes this.

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