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Thread: Weihrauch HW55

  1. #46
    Join Date
    May 2008
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    Quote Originally Posted by nick_mantis View Post

    What is the likelyhood of being able to get a replacement piston for an HW55?
    Having rummaged through my spare piston box this morning I have found a piston from a different manufacturer that would work in a HW55 --- the early SMK B2 piston.

    The early leather sealed B2 piston and in its converted to synthetic seal form will fit the HW55 with the minimum amount of work --- the only downside is that it will give 8mm less stroke than the HW55 piston, but at 6ftlbs that shouldn't matter.

    NOT this late B2 piston :-

    image.jpg



    The B2 synthetic converted piston would need machining down to sub 25mm on the flared front and rear sections as it's designed for a 25.4 cylinder, the cutout in the latchrod for the trigger sear would need deepening by 1mm and the seal would need changing for a TX200 one --- that's about all you'd need to do for an 8mm short stroke piston.

    Now if you wanted more stroke, you could machine off the welded on SMK synthetic seal seal adaptor and move the seal back to gain 5.5mm of stroke --- obviously the cocking lever slot in the piston would need extending rear wards to suit.



    The only modification needed to the gun for this to work is the drilling out of the latchrod hole in the back block to 10mm.





    All the best Mick

  2. #47
    Join Date
    May 2008
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    Here's a HW50 and B2 piston side by side for comparison :-

    image.jpg

    image.jpg


    From the first picture you can clearly see the 5.5mm section behind the seal on the B2 piston which could be removed.

    Some dimensions:-

    HW50 piston weight = 202g

    B2 piston weight = 222g

    HW50 stroke = 65mm

    HW50 stroke with standard B2 piston = 57mm

    HW50 stroke with B2 piston with 5.5mm seal arbor removed = 62.5mm


    It could well be the case that the B2 latchrod is brazed into the piston nose and if so it should be possible to heat the piston's head to melt the braze and then simply knock the rod forward to increase the stroke.



    All the best Mick

  3. #48
    edbear2 Guest
    P.M. sent about possible fix, have posted this to bring thread up to the top for the O.P. (you also have P.M.) as is time critical, so hope he spots it!

    ATB, Ed

  4. #49
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    Apr 2007
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    Dudley
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    Hw55

    Just found this on the web with the mention of the alloy piston head.
    The thing about the HW55 is that a lot of though went into balancing the powerplant to keep recoil to an absolute minimum. They don't give this kind of attention to any of their other guns.

    They had 25mm pistons, but were much thinner, and had a big slot cut from the side opposite the cocking slot to make it as light as possible. The nose of the piston was also aluminum to save a bunch of weight. Less weight moving at the shot, means less recoil and quicker locktime.
    But...
    A piston that light would have a ton of bounce. So they made the transfer port 4mm to eliminate the bounce which would destroy accuracy. They kept the leather seal so that it wouldn't deform when it smacked the front of the compression tube, and it also offered less friction in the tube.

    So with a 4mm TP would the internals from its sister the HW50 get the HW55 up to 10ft lbs.. ?

    Mach 1.5
    Last edited by Mach 1.5; 30-11-2022 at 05:22 PM.

  5. #50
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    Feb 2011
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    Quote Originally Posted by Mach 1.5 View Post
    Just found this on the web with the mention of the alloy piston head.
    The thing about the HW55 is that a lot of though went into balancing the powerplant to keep recoil to an absolute minimum. They don't give this kind of attention to any of their other guns.

    They had 25mm pistons, but were much thinner, and had a big slot cut from the side opposite the cocking slot to make it as light as possible. The nose of the piston was also aluminum to save a bunch of weight. Less weight moving at the shot, means less recoil and quicker locktime.
    But...
    A piston that light would have a ton of bounce. So they made the transfer port 4mm to eliminate the bounce which would destroy accuracy. They kept the leather seal so that it wouldn't deform when it smacked the front of the compression tube, and it also offered less friction in the tube.

    So with a 4mm TP would the internals from its sister the HW50 get the HW50 up to 10ft lbs.. ?

    Mach 1.5
    Chase the power in a 25mm Hw50 but let the 55's shot at the power they were intended for
    Hw77+7

  6. #51
    Join Date
    Nov 2010
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    Exeter
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    208
    The bespoke HW55 piston I bought here back-along weighs 180g, so about mid-way between the 50 and 55. Not fitted and tested yet but will my 55T enter the 'Goldilocks zone'...?

  7. #52
    Join Date
    Jun 2012
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    Quote Originally Posted by HW55T View Post
    Chase the power in a 25mm Hw50 but let the 55's shot at the power they were intended for
    Or do the opposite- use the heavyweight gun when you want to push power out of the system...
    Too many airguns!

  8. #53
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    May 2008
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    Quigley Hollow, Nuneaton
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    Quote Originally Posted by Epicyclic View Post
    The bespoke HW55 piston I bought here back-along weighs 180g, so about mid-way between the 50 and 55. Not fitted and tested yet but will my 55T enter the 'Goldilocks zone'...?
    It's fairly easy to machine 20g off a HW50 piston and long stroke it at the same time using a TX200 seal, but I found I had to weight the piston back up to 200g to get a nice firing cycle.

    It'll be interesting to see what it runs like with the 180g 65mm stroke piston.



    All the best Mick

  9. #54
    Join Date
    May 2021
    Location
    Oxted
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    35
    Right a little update for you all with some details. RobMC kindley sorted out an original (used) aluminium/steel piston for me, but stock unlike my previously repaired one. When it arrived gave it a good cleanup, fitted the O-ring seal, brass spring seat and washer from my own piston and also assembled everything back together also using my original spring.
    After taking everything apart again and putting it back together with the cocking latch the right way up this time the action was smooth and everything worked perfectly with a test shot into a flowerbed.

    Comparison without anything fitted. Only 3.68g difference and mine did not have the original pin fitted but a bit of a bodged one.

    My Piston: 149.48g (weighed after it broke and possibly a bit underweight)
    RobMC's replacement: 153.16g (no repairs and cleaned)

    I have been down the range this week and completed 3 rounds of competition targets that had to be handed in this week to avoid a forfeit. After having a month off with no rifle to keep my eye in while this was going on I was a bit wobbly but that will get better again. However my Weihrauch still appears to be performing very well with no issues from the failure. I will be stripping everything on a regular basis though to keep an eye on how the new piston is holding up! Still 14 rounds of targets to complete for the winter.

    I will confess that I do use a 3P shooting jacket and a glove to rest the rifle on my left palm, but otherwise just jeans and trainers. No fancy headgear, trousers, blinders, modern sights palm rests butt plates etc etc.
    10m standing using NSRA paper targets (5 on a sheet moving around the card)

    Would be interesting to see if anyone else it still using a Weihrauch for competition and what scores you are getting. I presume I might be the only one still using a springer in the Middlsex and Surrey county competitions


  10. #55
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    May 2008
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    Quigley Hollow, Nuneaton
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    Good result Nick --- well done to you, and well done Rob.



    All the best Mick

  11. #56
    Join Date
    Apr 2012
    Location
    Retford, Notts
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    34,742
    Excellent result, chaps.. I hope all keeps going smoothly.
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 4/5, 2024.........BOING!!

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