Preferred muzzle energy/pellet speed

Discussion in 'Piston & Spring' started by Cooper_dan, Jul 3, 2018.

  1. Finners1960

    Finners1960 Member

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    Hi Jim, I found that the ptfe sleeve was the culprit. Without it, and running at 10.3ft/lbs it was much more consistent over the chrono.
    However, the ‘boing’ was back!! I thought a little more preload might help, so I added a washer to the bottom of the piston and one at the spring guide end too.
    Over the chrono, 7.9’s were just over 800 ft/sec. Remembering your lgu article in AGW, I swapped to 8.44 Exacts. 775 ft/sec; 11.25 ft/lbs.
    Now, for years I’ve preached 10 to 10.5 ft/lbs is the place to be with springers. However, my lgu likes to run above 11... made apparent when (and this is not boasting) I put 10 pelets through a 12mm hole at 30 yds!!
    Hold sensitivity is much better and no discernible increase in recoil.
    I think I’ll leave things as they are now!
    Thanks again those that gave input.
    Sorry this reply is sooooo long!!
    Jez.
     
  2. Cooper_dan

    Cooper_dan Well-Known Member

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    Jez, glad you got it sorted :)
    Leaving things alone is the hard part, but turns out it's worth it in the end. Learnt that the hard way :rolleyes:
     
  3. bigtoe

    bigtoe Member

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    The front tophat needs to be 26mm total length, 4mm flange, the rest set to spring and the inner reamed to bang on 10mm, the tophat needs to just rotate nice with the spring pushed on and the tophat on the piston rod.

    At 26mm long the tophat will be sat around 2mm or so from the rear guide when cocked and will fully support the spring when in a cocked state, it also helps numb the vibration from the spring during the firing cycle.

    LGU and LGV rear guides are actually a little sloppy, they work, but a tighter fitting guide to the rod helps also, do not lube it though as it induces drag. The one bonus with the LGU and LGV pistons is they have straight piston rods, so tight guides can work very well.

    There is absolutely no need to sleeve a stock LGU or LGV piston.
     
  4. Finners1960

    Finners1960 Member

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    Thanks for your comments. All very informative.
    In the end, I decided to change the spring for a TX200 Mk3 factory original. This is something that Jim Tyler mentioned.
    The difference is dramatic! This spring was a tighter fit on the guide and top hat. The result is a softer shooting cycle and after small modifications, 10.8 ft/lbs with only 8ft/sec variation over a 20 shot string over the chrono!
    At last, I have my LGU here I want it for FT.
    Many thanks to Jim for his help obtaining the AA spring.
    Jez.
     
  5. Nomads HFT

    Nomads HFT Well-Known Member

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    No magic, Jez, just a softer spring giving gentler initial piston acceleration/recoil, a bit more preload to suppress piston bounce/surge. The main advantage of the TX Mk.3 spring is that it's like the Duracell bunny and goes on and on; it's set to length and less prone to creep than other springs I could mention.

    I'd keep an eye on muzzle velocity in winter temperatures; you may need to reduce preload a tad to keep at 10.8 ft. lb.
     
  6. Adam

    Adam Well-Known Member

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    Is this a drop-in replacement?
     
  7. Nomads HFT

    Nomads HFT Well-Known Member

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    Not really Adam. It will fit, but is crying out for new properly sized (15mm diameter) guides, and will need preload washers.
     
    Last edited: Jul 19, 2018
  8. Finners1960

    Finners1960 Member

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    To add to what Jim says Adam; I’ve found the AA supplied, TX200 spring to be so much better in fit and ultimately the shot cycle.
    For the sake of £20, try one! As Jim says, you will need a power washer to add length to the spring.
    I shot mine around the FT course at Pontefract for the first time yesterday. It’s now exactly where I want it to be.
    Watch out at the PJ British Champs... I’m out to get you!! Haha!!!
    Jez.
     
    custompaint and Adam like this.
  9. Adam

    Adam Well-Known Member

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    Last edited: Jul 22, 2018
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  10. bigtoe

    bigtoe Member

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    A Mk3 spring will rattle around like crazy without the right size rear guide...if anyone wants to test one of my Mk3 clone springs with guides that fit in an LGU you can PM me, if anyone wants to test my 25mm LGU vs one with a Mk3 TX spring that could be arranged also, this LGU uses a stock tired spring with a much improved skirtless 25 dual seal 180g piston and makes effortless power with possibly the softest recoil i have felt from a 25mm gun in .177.
     
  11. Adam

    Adam Well-Known Member

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    Jez is saying (post#44) his mk3 TX spring is a tighter fit than the std spring.
     
  12. bigtoe

    bigtoe Member

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    TX springs (Mk3) has an ID ranging from 14.8 to 15.05mm depending on who wound the springs that day, the ID of the stock LGU spring is closer to 14.3mm, so a MK3 TX spring is going to buzz on a LGU guide.
    Mk3 springs average rate is around 5.7N/mm, the fact the spring needs excessive preload adding means really imo its not a good choice, an older spec HW95 spring works extremely well and in some cases will go right on or very close on right on the LGU guide and can be had in lengths close to 255mm so plenty long enough. The 95 spring is also around 6N/mm rated or just a midges over so close on ideal.

    The big problem with the LGU is the seal, i used to love em, now after a ton of testing i now realize they sap a ton of power, take a close up high res pic of the wording on an LGU seal and you will see they are manufactured with a lip at 25.4mm, i have actually heated one to 40C and seen the lip closer to 25.8mm, no wonder some lads suffer huge power losses when the gun gets hot and see big power gains when in cold weather as the seal shrink so essentially size themselves in better.

    I have springs here that work in the LGU and LGV, they are a Mk3 tx clone but use 3mm wire not 2.95, they are shorter than the stock Mk3 spring as i had them sized to fit TX 22mm conversions, they work and shoot well but again need lots of additional preload to get them up at the rate needed. I'm testing one right now in a TX .22 Rifle at 93mm stroke with my dual seal set up 25mm and its working incredibly well, in the .177 HC it needed around 8mm more preload which is around what a stock piston weight delivers and remember the stock spring is around 8 to 10mm longer than these springs i have here so its pretty efficient.

    So Jez can't be using a mk3 TX spring, if he is its a friday afternoon spring that was wound tighter than normal and it just happens to fit his guide ok, most of the ones i have tried rattle and buzz. The spring needs to slide down snug on a 14.3mm guide, old 95 springs and some diana springs do as mentioned earlier.

    A LGU seal and its 25.4mm sizing....

    https://photos.app.goo.gl/bAJZSfiRx1JUQe3p9

    I run 25.05mm on the lip now and run an O ring right behind the seal at 25.3mm OD, 3.5mm port, just adding the O ring and sizing a seal down brought an LGU here from 10.2 to over 12fpe with the stock tired spring previously used, i had to lose the installed additional preload to get the gun around 11.2fpe. Its amazing to see you all messing with springs when the seal is the first port of call and the port, get the seal more efficient, balance the piston weight to the port and the spring will suddenly start working way better.

    https://photos.app.goo.gl/xxYRCU18oVNwNLJaA

    The tophat is steel and carries another bearing for the piston nose....you see the seal layout though, that spec needs no shove to get the piston moving from rest, it falls under its own weight, when hot the front seal swells and starts to seal without relying on the O ring but only swells to around 25.2 to 25.25mm which is still within working range and minimal frictional losses, when cold the front seal acts as a buffer only as it shrinks and fails, the O ring does the sealing now. Tested at 40C+ and -6C right out the freezer with reasonable velocity stability.

    Managed to find a HW95 spring set up on the LGU skirtless, piston showing dual bearings and the rear guide reduced in OD to suit the ID of the 95 spring...very little frictional loss, easy power with this, easy to set and fatigue is minimal.

    https://photos.app.goo.gl/GNVJgpiZjN772cGv5

    https://photos.app.goo.gl/ptNi5q2s7pB7oRjMA
     

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