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HW90 0.177 over 20ft lbs ; My experiences

Discussion in 'Airgun Reviews' started by hw90hw90, Dec 29, 2013.

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  1. hw90hw90

    hw90hw90 Member

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    I've posted this on another thread here, but thought it a shame not to encourage others who dont have a 0.22.

    So I'm in the process of a barrel swap over from 0.22 to 0.177. But to start with I write about pellet choice.

    PELLET TESTS 0.177 HW90 Standard barrel length

    (sorry I don't have a carbine model )


    For pellet tests in 0.177" cal, a good site to look at for pellet sizes to use on the HW90 in 0.177 is this US site;


    http://www.straightshooters.com/weih...177-beech.html

    Note the varied muzzle energy output. The most you will expect on a 0.177 pellet is 20 ft lbs or 26 Joules. Thats what I want to fire the HW90 at! H & N match comes out as an 25 Joule pellet.

    Try this energy calculator here for yourself;

    http://www.pyramydair.com/article/Wh..._August_2003/5


    BREAKING THE SOUND BARRIER WITH A HW90, 0.177" CAL

    As per the muzzle velocity data, the HW90 in 0.177 has the highest pellet velocity of 1097 ft/s (cub pellet,fifth down in 0.177 list).
    My speed of sound figure of 1125 ft/s is for a temperature of 19 .5 DegC . As temperature drops the speed of sound decreases.
    I use the speed of sound calculator here http://www.sengpielaudio.com/calculator-speedsound.htm

    and if you set the calculator to celsius and enter in a temperature, like 19.5C , push calculate, you get 1125 ft/s approx.

    So for the CUB pellet at 1097 ft/s at what temperature would you be close to break the speed of sound (or achieve MACH 1)
    with the HW90???


    do a guess and check with the calculator and I get 5 deg C.

    So for a bit of fun shooting in the winter with the HW90 could be quite entertaining. Quite cracking literally!!!

    now what does cold do to the gas inside the weihrauch HW90. Thats another question.

    Look here ...http://www.pyramydair.com/s/m/Weihra...Air_Rifle/2358

    find the rifle pictures and you will come across a comic of a guy firing a springer on a cold day, and the other guy says," you would not have the same problem if you had a gas ram (like in a HW90 but filled with nitrogen!)

    I'm no expert....but i want to answer this question : Is the pressure change significant in the gas strut when the temperature drops from 20deg to 5 degC??

    ----my ANSWER------- WARNING: read this if you like formulaes -------otherwise don't ------------------------------

    combined molecular mass air is 28.97g/mol http://www.engineeringtoolbox.com/mo...air-d_679.html
    volume of theoben gas ram uncompressed, 0.00005m3 (my guess!)
    air density 20deg and 5 deg , from http://www.engineeringtoolbox.com/ai...ght-d_600.html

    mass of air at 20degC = 0.0000602kg
    mass of air at 5 degC = 0.00006345kg
    moles air(20deg)= 0.0000602 x 1000 /28.97 = 0.0021 moles
    moles air (5deg) = 0.00006345 x 1000/28.97 = 0.0022 moles

    I found number of moles of air has hardly changed in the drop from 20 degC to 5 degC

    to confirm this use http://www.ajdesigner.com/idealgas/index.php

    I want to calculate the pressures in the theoben gas strut,and it should give me 26bar at 20degC.It did not!.

    This is where I got stuck ...so fudged it using n=0.0135moles, T=20degC, V=0.0000125, giving --> P(20)= 25.98bar
    then used n=0.0135moles, T=5degC, V=0.0000125, P(20)= 24.65bar
    Change in pressure = 1.3bar or 5% less pressure and perhaps 5% less velocity!

    LOOKS like I guessed either the wrong VOLUME of the theoben strut or calculated the moles incorrectly
    or both

    But I still conclude that the gas pressure in a HW90 decreasing from 20degC to 5 degC is not significant BUT
    could make cracking the sound barrier like chasing your tail....why?


    As the temperature drops the speed of sound drops which makes it accessible to the HW90 muzzle speed. But at 5DegC, there has been an 5% drop in gas pressure which will cause a drop in pellet speed.
    YOU MAY NEVER break the speed barrier


    ------------------------------------------------------------------------------------------------------
    BEST PELLET CHOICE HW90 0.177?

    Which pellet to use in 0.177? Too light pellet --> more piston SLAM --> could damage the HW90.
    Too heavy pellet --> less piston slam, but higher temp for piston...as pellet takes longer to exit increasing the pressure and hence temp...more likely to compromise the piston seal (shorter life)

    So I would start with an inbetween....see http://www.straightshooters.com/weih...177-beech.html

    lightest is 6.5 grain (laser)..heaviest 11.5 grain (silver arrow) --> average 9.05 grain

    JSB exact is a winner 8.44, H&N match 8.02, these are safe bets
    ------------------------------------------------------------------------------------------------------------------

    RABBIT HUNTING DISTANCES
    So now I'm thinking about accurately firing a 25Joule H & N pellet at say a rabbit, with a flatter trajectory than a 0.22, and I ask myself...

    How far away can I be to get a head shot kill?
    How big a prey can I kill at that max distance?
    Why?, the further away I am the less likely I will scare other prey away, while reloading and can keep hunting.

    The answer to distance and prey size is found in the BEEMAN research found here;

    http://www.beemans.net/field use.htm

    According to this article you need a min of 8 foot pounds (ft lbs) to kill a jack rabbit (see second table).....8 foot pounds for a H & N 8.2grain ,0.177 pellet is 670 ft/s and 11Joules. (using above energy calculator)

    So the new question is.....How far away from the rabbit can a 0.177"cal 25Joule pellet be, to not have an energy of less than 11 Joules??( or not more than 56% energy loss)?????

    Again from the above beeman article, in the Table labelled ,field velocity , for muzzle velocity of 1000 ft lbs ,for 0.177 cal and 7.8grain.....remembering we need energy of 11 Joules, so put 7.8grain, 680ft/s in above energy calculator and you get 10.9 Joules ---> distance = 30 yards!!! (27.4m) according to beeman!

    quite close! But as I have found,my weak air rifle claimed black birds at 30-40m so I'm betting on better distances with the HW90!

    thanks for reading, I will progressively add to this thread based upon real hunting data.

    Rick
     
    Last edited: Dec 29, 2013
  2. dave goodall

    dave goodall Donator

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    At 1000 fps you will be lucky to hit a rabbit with 177 esp as light as jsb it could land any where u obviously have done your home work on formulars but not on actual pellet stability ;) Even with 22 ect stabilty faulters at such speeds unless decen weight behind them think u would be better going high weight tbh for long range shooting breaking the speed barrier is a bad thing with pellets as they loose stability and groupin is a joke thats if the pellet even stays true and dosnt tumble
     
    Last edited: Dec 29, 2013
  3. dave goodall

    dave goodall Donator

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    Ps also your gasram will also burn out very fast at such powers id of thought unless a fac rated gasram fitted there more too them than just filling with higher pressures
     
  4. hw90hw90

    hw90hw90 Member

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    I have a problem with thread hijackers.

    If viewers read this thread, they will see that I did not mention air rifle pellet instablity problems in full power 0.177 HW90s.

    That is because I have decided that full power HW90 air rifle pellets, never reach MACH 1, what ever the temperature, based upon the pellets I have reviewed. How I reach that view is entirely tracable.

    Also I have never witnessed slug instability in full power 0.22 HW90 either. That is based on experience using a wide range of pellet grains weights and brands. Shot over short and long distances. There are probably many other reasons why pellets become unstable also. The shape of the air rifle pellet counters rotation.

    Thats my hypothesis ( I intend to either prove or disprove it ).

    To keep this thread tangible, only reply to it, if you meet ALL of the following requirements;

    1. Write sentences grammatically and check them for errors.
    2. Support any claims with data from reputable webb sites.
    3. Own a HW90 or want to own one

    Please do not claim tumbling or instabliity of air rifle pellets in 0.177, when you have never owned an HW90 at full power, and claim air rifle pellets are unstable based on what other people tell you.

    That's laughable.:down:

    Rick
     
    Last edited: Jan 1, 2014
  5. Pidlar

    Pidlar Big Poster

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    You have posted on an open forum, thus encouraging discussion an comment on the views you have posted from other forum members.

    If you so wished that nobody should reply after reading all of your data then really you should have stated so in post #1.
    Finally I have no idea how many forums you are a member of, but discussing a topic raised by the original poster is not hijacking a thread!!!!!
    Happy New Year


    Just another point, after stating that people must grammatically check their posts for errors in requirement No.1. You spelt web with a double b in the requirement No.2 !
     
    Last edited: Jan 1, 2014
  6. Tadpole

    Tadpole Super Moderator Staff Member Mod/Admin

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    As this information is of very little use to us in the UK, the op is in Australia :closed_2: ..................... :coffee:
     
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