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Thread: Spring Gun tuning - Top Hat advice

  1. #16
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    You want the guide to be able to rotate.
    Machine the end plug to look something like this:
    http://www.airgunspares.com/store/pr...-Part-No.-V15/

    Then you can make a rear guide with an end flange, and a hole that fits over the stub you left on the end plug.
    Add a thin steel washer between the delring guide and the end plug to facilitate rotation.
    Make the guide about 0.05mm larger than the spring ID for a really tight push fit. This may reduce power a bit, but will kill most vibration without adding lagre amounts of grease.

  2. #17
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    This is a good example of how a guide will look if you leave a rear centering stub:
    http://www.airgunspares.com/store/pr...er-%26-Osprey/

  3. #18
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    This is interesting , it doesn't really matter if your long bit is at the front or the rear, if its a thin walled guide the piston rod actually helps strengthen it if at the front , however you do it make sure both ends are located centrally and make them so they just contact when cocked , full support and no odd coil sticking proud when cocked .

  4. #19
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    Iím just a bit pissed off now , I received the delrin rod today and despite the listing being for 10mm & 12mm diameter, the 10mm as suggested is a bit too loose and the 12mm is actually 12.22mm, 0.12mm BIGGER than the ID of the spring....grrrr

    Thereís no mention on the site of the diameters being Ďnominalí so it looks like a phone call on Monday

    The company in question is HPC Gears of Chesterfield.

    Iím not sure Iíd be comfortable machining 0.22mm of the length of it ( 200mm ) on the lathe although I do have a live centre for the tail stock so it might be within my means.
    I only need a piece 125mm long so unless they can provide me with another bit of exactly 12mm diameter itíll mean a bit of careful work.

    The 10mm piece is also over at 10.15mm but too loose

    Norm
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  5. #20
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    That extra material makes it possible to machine it to spec.
    You might need to do some fine adjustments on the lathe to eliminate taper when you machine it to size.

  6. #21
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    Quote Originally Posted by evert View Post
    That extra material makes it possible to machine it to spec.
    You might need to do some fine adjustments on the lathe to eliminate taper when you machine it to size.
    Yes youíre right, and it looks like I owe HPC a mental apology, much further down the listing past all the other adverts is a bit about the tolerances and 12mm is +0.2-0.7mm. Looks like Iíve some machining to do

    Norm
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  7. #22
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    Quote Originally Posted by Mr.Fixit-Norm View Post
    Looks like Iíve some machining to do
    Thats the fun part

  8. #23
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    Quote Originally Posted by evert View Post
    Thats the fun part
    Haha , yes, but only when you get it right
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  9. #24
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    I managed to spend some time in the workshop this afternoon and successfully machined the 12.2mm delrin rod down to 11.95mm, this gave an approximate 0.05mm gap between that and the spring. It wasn’t that easy to do, even using a live tail stock the rod had a tendency to spring away from the cutter when I was machining the middle part. ( I’m guessing that’s what evert was referring to ? )

    I overcame this by taking very fine cuts, ending up with a rod that was a nice smooth fit in the spring. I then machined the old guide off the plug and while it was still centred in the lathe, drilled a 10mm hole right through.

    I then machined 15mm of the end of the Rod down to 10.1mm which allowed for a tight fit in the plug ( careful application of a mallet )

    I trimmed the guide down to 115mm which I guessed to be the maximum I could get away with but that was a bit too close for comfort when cocked so I took another 5mm off.

    I found a nice new shiny 2mm thick plated washer which was a perfect fit in the end of the piston, not to tight so I couldn’t get it out but tight enough so it won’t move sideways , with the top hat thickness this gives 5mm of pre-load.

    Once assembled with a decent amount of moly grease on the spring, guide and top hat, and back in the stock I found it was marginally harder to cock but not enough to be an issue. When I fired it there didn’t seem to be any twang whatsoever and despite the heavy trigger it seemed smoother and with virtually no recoil !
    Not sure if the lack of recoil is a real effect or due to my rose tinted safety specs - lol

    I didn’t have a chance to chrono it but I’ll try that tomorrow. I don’t know if what I’ve done will affect the power, I’m not worried if it doesn’t as the exercise was to quieten and smooth it, but it’ll be interesting to see what the result is.

    Unfortunately I didn’t take any pics of the spring guide but it looks just like the original one but 110mm long rather than 49mm

    Norm
    Last edited by Mr.Fixit-Norm; 06-06-2020 at 11:21 PM.
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  10. #25
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    Put a few shots over the chrono today and surprisingly the power is unchanged at an average of 8.7ftlbs

    The fps variation is about the same as well, but itís definitely lost the twang and there is also less recoil, so all is good

    Iím currently putting JSB Exact pellets through it as apart from a few old Bisley Magnums, these are the only 0.22 pellets I have. The thing Iíve noticed is the heads on the JSBĎs are a bit tight to get into the breach. Theyíre 5.52ís and Iím wondering if 5.51ís or 5.50ís would be better, as one of the JSBs I put over the chrono went into the breach much easier and that one pellet gave 9.3ftlbs compared to most of the others which gave 8.5-8.8.

    I know itís not about power but accuracy and they are quite good but Iím concerned that if the heads get marked when they go into the breach, it might affect accuracy.

    Any thoughts appreciated.

    Norm
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  11. #26
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    Sounding good and suitably de-twanged, Norm.

    If you can, get hold of some RWS Hobby and JSB RS. These tend to give higher outputs in lower tuned springers. If the power isn't uncomfortably close to the limit (doubting it will be), it sounds like you'll have plenty of scope to raise power by increasing the preload, if required. Maybe a 5mm increase to start with and then going in 2mm increments?
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
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  12. #27
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    Sound like success!
    I dont think you want to push those guns very much faster, but as Tony says, lighter pellets will probably give you a bit more energy and velocity.

  13. #28
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    Quote Originally Posted by TonyL View Post
    Sounding good and suitably de-twanged, Norm.

    If you can, get hold of some RWS Hobby and JSB RS. These tend to give higher outputs in lower tuned springers. If the power isn't uncomfortably close to the limit (doubting it will be), it sounds like you'll have plenty of scope to raise power by increasing the preload, if required. Maybe a 5mm increase to start with and then going in 2mm increments?
    Quote Originally Posted by evert View Post
    Sound like success!
    I dont think you want to push those guns very much faster, but as Tony says, lighter pellets will probably give you a bit more energy and velocity.
    Cheers Guys,

    I think given that this gun is just a bit of fun ( remember that stock ), Iíll keep the power where it is, my main aim now is to find the best pellet for accuracy. Despite the heavy trigger it feels quite nice to shoot

    Iíll see if I can try and get some of the pellets you recommend Tony. Iíve had a look on the Intershoot site and they donít quote a size for the JSB RS which is a shame. I wonder if thereís any way to find out ?

    Norm
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

  14. #29
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    Quote Originally Posted by Mr.Fixit-Norm View Post
    Iíve had a look on the Intershoot site and they donít quote a size for the JSB RS which is a shame. I wonder if thereís any way to find out ?
    All the JSB RS pellets I have seen have been 4.52mm and 5.52mm.

  15. #30
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    Quote Originally Posted by evert View Post
    All the JSB RS pellets I have seen have been 4.52mm and 5.52mm.
    I thought they might be, 4.52 & 5.52 are the common size which seem to fit 90% of anything out there. Iíve got a custom made 0.22 pellet sizer somewhere, not sure if that will have any effect on the heads, probably only does the skirt.

    It might be a case of trying some JSB Exacts in 5.51 or 5.50

    Iíll nip over to the Chinese UK forum and see what pellets are commonly used by other DB4 / DB5 owners

    Norm
    Now retired I planned to concentrate on my shooting & other hobbies, but my better half seems to have other ideas - she's on page 4 of the list of things to do www.thatsmypicture.co.uk or www.thatsmypicture.ddns.net

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