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Some hw95 modifications as promised

Discussion in 'Anything Airgun Related' started by wonky donky, Jan 3, 2014.

  1. wonky donky

    wonky donky Donator

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    This is a test bed rifle so certain things have been done so adaptations can be made later.

    I will add to this thread as & when I get time.

    Please feel free to reproduce any or all part of anything including images in this thread.

    Rifle stripped degreased, first thing,

    Trigger. Does it need to be polished? MY opinion is if you want a very fine predictable unit to use indoors for target shooting then maybe. If you going to use it outdoors in all climates then the Rekord unit can be set up very nicely without polishing sears & the risks that come with it. Trigger weight spring can be changed for lighter or heavier versions. The let off point can be adjusted using the torx screw & the length of first stage with the tab in front of the blade.

    One modification Bigtoe01 (Tony) advocates & one I have done with a little more added & that’s to replace the soft steel pin used to hold the trigger blade with a hardened steel pin with two “shim washers”

    My method is to use the existing holes, if you look at the unit you can see the pin is larger one side than the other as its “peened “over a little. If you knock the existing pin out from the narrow side you will find the location hole is slightly smaller, enough to just grasp & hold the new 2mm hardened pin you are putting in.

    The other thing I do is remove a small amount of material from each side of the blade reducing the thickness where the locating holes are & insert a Shim Washer 0.3mm thick each side of the blade. You don’t want any side to side play in the blade so go carefully, its better if you need to prise the trigger case open A FEW THOU! That’s 3 or 4 thou not 30! To refit the blade.

    Standard pin at the top

    New pin & shims in place
     
  2. mark.177

    mark.177 Donator

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    nice one! will be following this with interest;)
     
  3. nick2

    nick2 Keyboard Hero

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    I will be following this with interest too. I missed out on a s/h Venom 95 over Christmas, it was advertised on the BAR site at £295.00, a good price I thought.
     
  4. The Robin

    The Robin Super Moderator Staff Member Mod/Admin

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    I will be following this thread with interest and I've heard very good things about you wonky donky :up:
     
  5. wonky donky

    wonky donky Donator

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    Being a test bed rifle the barrel will be changed for a different calibre a few times so to make this easier & avoid removing the stock I have removed the rivit holding the cocking lever in the breech block. Just knock it straight out with a punch, a roll pin punch is best for this.

    With the pin out bore each end with a 2/2.5,, starter (centre) drill allowing the counter bore part to go in a mm or so then take 1/1.5mm of each end.

    Drill & tap straight through M3.

    Select 2 M3 countersunk screws the appropriate length & fit the part into the breech to make sure the screw heads are flush with the breech block. If the the screws are even slightly proud of the block then they will damage the inside of the stock on the later rifles so be warned.

    Everything looking good permanently Loctite one screw in place, clean the Loctite out of the threads on the other side of the pin & leave to cure. when cured reassemble & it should look like THIS

    Just to clear something up for one or two members, when we talk about Loctite we mean Threadlok, Bearinglok, & Threadseal...................NOT LOKTITE SUPERGLUE ;)

    You have to thank Bigtoe01 (Tony) yet again for this one.

    Someone emailed me to say the M3 screw can come lose due to friction, to a point he is correct. this can happen for a number of reasons. If the screws are tight into the breech chamfer, or there is miss alignment causing the screw to bind on the breech, if the surfaces were not clean when the loctite was applied can all cause a screw to loosen. the bearing loctite will be stronger than a 10.9 M3 scew so the one that may need watching is is the removable one. I use a loctite that can be undone with hand tools in this area.

    Thanks Paul, I try to think of everything but rarely do! :eek:
     
    Last edited: Jan 3, 2014
  6. thevoid

    thevoid Posting Addict

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    All that text and no mention of the top secret modifications lol
    I know you're sweet on the current spring but can we have a look at how the mk1 77 goes with the current config?
    Ta
    Paul
     
    Last edited: Jan 3, 2014
  7. wonky donky

    wonky donky Donator

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    Paul I'm doing the little easy things first, the modifications WILL get more complicated & specialised as we go.

    The spring in the rifle IS NOT ONE OF MINE, & to be honest it's far too stiff even though it's made from the same wire. Springs are quite a way down the road yet, sorry mate, I will do what you want but if I go that route now it will just negate the work I've currently done & intend to do next. Don't forget this IS an experimental rifle.

    As I have said to you, I have some MK1 77 springs & willing to send one for you to try in your rifle.
     
  8. thevoid

    thevoid Posting Addict

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    At this rate you'll have to grind off the name and model from the gun as it wont resemble a Weihrauch at all ;)
    I'll email you re the 77 spring if only to give Pete something to moan about
     
  9. wonky donky

    wonky donky Donator

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    I have opened the transfer port from 3.2mm to 3.55mm that's about what a 3.6mm drill will give you, maybe a touch more. there's nothing wrong with using a drill bit if you can get one long enough so as not to damage the breech jaws. If not a standard drill of the size you wish to use can be used to put a hole in a length of braas rod & then fix the bit into the rod with some Bearing Loctite.

    Doesn't matter what you use or if you open the port from the cylinder or breech the port will need to be countersunk very slightly from both sides, reaming isn't a must but is preferable.

    I go into the cylinder with a hand tapered reamer that I have fixed into a length of small diameter rod with a "T" handle on the end. I locate the reamer into the port & under it's own weight gently tiwist, I can just feel it cut, 1 turn is enough.

    I then do the chamfer in the same way using a small sharp countersink bit.

    The tiny chamfer on my port can easily be seen HERE. The chamfer inside the cylinder is the same & is about 0.5mm deep.

    Next thourly clean the clinder to get the swarfe out
     
  10. Jackroadkill

    Jackroadkill Donator

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    What effect does this have, Wonky? I know that people approach it with trepidation but I'm still in the dark about what the purpose and effect of it is.

    Cheers,

    JR
     
  11. mark.177

    mark.177 Donator

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    just my 2p worth and will be honest have no clue but did here a chap talking about it years ago. the piston moves forward under speed compressing the air as it goes but the pellet doesnt start to move forward in the barrle till the piston has reached the breach end of the compression chamber. at this point all the air from the cylinder has been compressed into the area of the port and pellet skirt and is very high pressure it is only then that the pellet starts its way down the barrel. increasing the size of the transfer port decreased the pressure at the moment the pellet starts to move lowering power. a by product of this was also that the piston would move quicker down the compression chamber and increase the end recoil and hold sensitivity... i think if you do this you also need to increase the swept volume or something? but then im not a tuner.
    it was a long time ago and i may be completely wrong but the chap i saw said you only need to polish/chamfer the transfer port a tiny tiny amount... unless its to small to start with and the pellet is moving before the piston has come to a halt? am i barking up the wrong tree?
     
  12. wonky donky

    wonky donky Donator

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    No at a rough estimate the pellets about 2" down the barrel before the piston has reached the breech. It has already been proven using state of the art scientific equipment the piston will bounce off a cushion of compressed air in front of it even without a pellet in the breech! Not what we have been brought up to believe eh?

    The idea is to balance the system fine tuning the surge, (piston bounce). Some rifles have the TP too small, the air can't escape, builds pressure & the piston bounces back giving quite violent piston bounce in some cases. This is often why putting a big spring in something like an Airsporter reduces power but the rifle feels like it's trying to knock your teeth out. :D

    What I & others do is open the port delaying this process. I just happen to know through experience & exchanging information with Bigtoe01 & others the ideal port size for the HW95 with the modifications I'm doing is around 3.6mm.

    Opening the port up too much will cause the rifle to feel "Slammy".

    What I have not said yet is my rifle is Short Stroked & makes a big difference..............this will come later.

    DON'T GO OPENING UP THE TRANSFER PORT BY ANY AMOUNT ON ANY RIFLE IF YOU DON'T KNOW ABOUT SCR.

    For example the TP on my HW77 is 3.9mm dia. STANDARD IS ROUGHLY 3MM. again it's short stroked & got an "O" ring conversion. Recoil is almost non existent compared to a standard rifle.

    First we work out what the standard SCR ( Staic compression ratio) of a rifle is. To do this you need to measure & work out the volume of the transfer port then divide that in to the swept volume. the answer will be the SCR eg 500/1 & so on.

    For a given TP length there will be a range IN WHICH the ideal SCR will lie..............but it doesn't end there, piston weight also has to be taken into account.

    For my HW95 the ideal SCR would have been around the 300/1 mark IF IT WAS STANDARD, but, I've also lightened the piston which means it's going to accelerate faster, that means it will compress the air faster & react quicker to the cushion of air it creates so I needed to drop the SCR. It's currently 266/1.

    There a threads on the other forum right now about this, you really need to google it, far too much for me to try to explain here.
    How we arrive at this information in the beginning is to open the port out & tap it say M5. Inserts are then made with various size holes in, so in other words we make interchangeable transfer ports.

    For the ideal sub 12fpe rifle there is an ideal swept volume for each calibre, an ideal piston weight, etc. Most rifles are not designed for the UK power so we do what we can to make them better.

    hope this helps.
     
  13. Andy_J

    Andy_J Replica Airgun Enthusiast

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    Thanks for that Wonky. A great post. :up:
     
  14. mark.177

    mark.177 Donator

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    thanks, i guessed there would be more to it than that lol, you certainly know your stuff:)

    not that i've done it yet but just to clarify... i shouldnt drill out my 95's tp to 3.5mm if the rest is left as standard?
     
    Last edited: Jan 5, 2014
  15. wonky donky

    wonky donky Donator

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    I have reduced the diameter of the 95 piston, I do this at the same time as making the grooves if I'm fitting radial bearings rather than studs.

    Turning the piston in a four jaw chuck & getting concentricity by putting the dial gauge on the small shoulder of the nose of the piston at the point it meets the outer wall. I use this area because I have found in the majority of cases it's the outside sleeve of the piston that's not concentric, not the piston latch rod. This then means the latch rod & nose are concentric. Once the outside of the piston is machined & the grooves put in everything will be as good as it gets, well that's the theory & so far it's been fine.

    There are two problems though. first the tool will bounce & skip when it hits the cocking slot & at the same time the piston walls will collapse. all this will create chattering, poor finish & ovality. I use a interference fit insert made from brass, Delrin, aluminium or any other reasonably hard material will do. The tighter the fit the better as long as it can be removed without damaging the piston after.

    All I can say is it works for me. Bearings on the 95. Note the rear one is wider than normal & I have removed 3.5mm from the rear of the piston for later developments. I turn the inside & outside of the bearings to size & then fit to the piston.
     
  16. whitevanman574

    whitevanman574 bell target champion

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    opening the transfer port helps the flow of air guys , some say its like two big lads going through a door ,open it a bit more they both get through :)

    but not to much .

    theres a further debate what is the best power for an airgun to run at ...regardless of law ... just engineering ..
     
  17. thevoid

    thevoid Posting Addict

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    Great info again Dave, any idea on the piston weight with seal, top hat and liner?
     
  18. wonky donky

    wonky donky Donator

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    As far as this thread is concerned Paul the piston isn't finished, but of course in reality is been done a while now.

    I wanted 225gms all in with bearings, liner, two shim washers, top hat & seal. It ended up at 228gms so not too shabby!
     
  19. The Robin

    The Robin Super Moderator Staff Member Mod/Admin

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    Great info and pics, you certainly know your stuff and I'm finding this thread amazing and also owning a hw95k I'm very interested in this. Keep the info coming :up:
     
  20. thevoid

    thevoid Posting Addict

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    This for me is the single most efficient way of killing the muzzle flip on the 95, I'm running a very similar spec to Dave and during my experiments the light piston and wider port makes the gun behave much differently indeed
     
    Last edited: Jan 6, 2014

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