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Thread: FPS variation in an HW100

  1. #1
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    FPS variation in an HW100

    I recently chrono'd my HW100 over a whole fill of air, just to see what variation there was.

    It showed me that the shot to shot output varies by around 3fps with the very occasional 5-7fps.

    There is a gradual change across the whole cylinder of air, it starts slightly high, drops gradually, then climbs back up before dropping off again - more or less like a sine wave. I assume this is a characteristic of regulator. I don't think this gradual change is really very important, as long as it's not too big. On my rifle it's only 4fps change.

    Worst case the spread between the fastest and slowest velocity shots out of 113 shots was 10fps. The worst spread between any two consecutive shots was 7fps.

    What does stand out, is that the shot to shot readings nearly always go high, low, high, low. For example +2.8fps, -3fps, +1.6fps, -3fps and so on...

    I was curious if this is a real effect or just random chance and if it's real, what causes it.

    I have yet to compare FPS readings with pellet impact point to see if there is a strong correlation. In theory, if this was predictable and did have an effect on impact point, you could adjust for it with a slight change in point of aim, alternating high, low. Trouble is you'd have to synchronise with the changes in fps otherwise you could make the effect worse!

    Lastly, does anyone know what's involved in bringing the FPS spread down on the HW100? Is it even possible? Is a shot to shot variation of 3fps as good as it gets? Is what I'm measuring more to do with variation in pellets than what the mechanics of the gun are doing?

  2. #2
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    5-7fps spread is superb, your rifle is perfect
    you don't give cal or actual readings but if .177, 700fps (ish) all are +/- 1%. if .22 at 560fps (ish) all are +/- 1.5%.

  3. #3
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    Quote Originally Posted by angrybear View Post
    5-7fps spread is superb, your rifle is perfect
    you don't give cal or actual readings but if .177, 700fps (ish) all are +/- 1%. if .22 at 560fps (ish) all are +/- 1.5%.
    Sorry, it's a .22!

    Yes, I thought and average spread of 4fps was pretty good...

    I'd like to see if I can get my 50m grouping down a bit. It's about 1" at the moment. Lots of things contribute to that of course, but you've got to start somewhere!

  4. #4
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    Yes you can't moan at them figures.
    Any rifle putting out single figure variations is spot on in my book

  5. #5
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    Most tuned PCP's would like to see those figures . My tuned XTX AIR BSA ultra is 4-5 fps and my standard HW100k's are about 6-8 fps

  6. #6
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    I recently bought a new hw100 22 , it produces over 100 shots between 560 and 570 fps with 16grn jsb. I'm happy with that.

  7. #7
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    Here the graph. It's a 2009 gun I bought second hand. Very little use and never been apart.

    The barrel was shagged though...

    It's now got a brand new barrel on now.

    http://i1262.photobucket.com/albums/...ps9ekpckt9.jpg

  8. #8
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    Hi Richard, the hw100 regulator has a bit of "creep" at high cylinder fill the output will be higher, at low fill it will be lower. can be like 5%.
    it is not like a Vulcan or Cricket regulator where you have a firm hard seat, but it is using the ball bearing lifted off the rubber seat by the regulator piston. The guns knock open valve will sort out/compensate for this variation. so it is not critical.

    there is a video of a spanish guy on youtube who works the hw100, he polishes the hammer and the shuttle etc. if you have not had your action apart, worth trying. polishing helps.

    with my Vulcan(recommended), when i R2 chrony it (recommended) i am getting MANY duplicate readings in fps, which is something.
    I dont see this with hw100s.


    you can try to use different measuring equipment thats why i am linking you this
    https://www.youtube.com/watch?v=VsDoqHOFIEI
    i got mine from forguns_pl off delivered with no issues and it is the best chrony in my opinion.

    Edit:
    single digit deviations will NOT move the POI. so dont dwell on this.
    Last edited by krisko; 23-01-2017 at 06:19 PM.

  9. #9
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    Quote Originally Posted by RichardinDorset View Post
    I recently chrono'd my HW100 over a whole fill of air, just to see what variation there was.


    What does stand out, is that the shot to shot readings nearly always go high, low, high, low. For example +2.8fps, -3fps, +1.6fps, -3fps and so on...

    I was curious if this is a real effect or just random chance and if it's real, what causes it.
    Hi Richard

    Great figures overall and I totally agree with the 'saw tooth' pattern. I've been doing some chrono work with my HW100, AA HFT500 and AA S410 lately (sad man that I am ) and I've seen similar effects in all of them - it seems to be down to speed of shooting. Now I've got a Caldwell chrono that records data directly to my phone, I can rattle off a string as fast as I can load and pull the trigger, but if I do, I see the same sort of 'saw tooth' pattern for all my guns, regulated or not. If I slow down and leave about 10 seconds between shots the curve flattens considerably.

    I'm not sure exactly what is happening but I'm guessing that the air pressure takes a little while to equalise between the cylinder and the plenum and/or there is some sort of turbulence, or even temperature difference that needs to settle. I'm pretty convinced that the effect is real, as it is consistent and repeatable, although it's always dangerous trying to interpret results from the end-user chronos as many are so cranky and dependent on the exact set up, especially light conditions.

    Cheers

    Alan

  10. #10
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    Thumbs up

    +1 yes some hw100 regulators even whistle.

    it may take a few seconds for the regulated "chamber" volume pressure to stabilize, so dont rush the shots. especially when you are looking into the fps.
    plus dont forget even JSBs have 5% weight distribution pass/fail criterium so pellets will contribute to the issue too.

    i have seen the sinewave too, i think it is normal with the hw100. as long as the extremes are not wide apart - which are not, you are golden.
    Looking at your good results, I dont think you will improve much by polishing to be honest. Worst case you will break your gun. So something for your consideration.
    Last edited by krisko; 23-01-2017 at 06:31 PM.

  11. #11
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    Quote Originally Posted by RichardinDorset View Post
    I recently chrono'd my HW100 over a whole fill of air, just to see what variation there was.

    It showed me that the shot to shot output varies by around 3fps with the very occasional 5-7fps.

    There is a gradual change across the whole cylinder of air, it starts slightly high, drops gradually, then climbs back up before dropping off again - more or less like a sine wave. I assume this is a characteristic of regulator. I don't think this gradual change is really very important, as long as it's not too big. On my rifle it's only 4fps change.

    Worst case the spread between the fastest and slowest velocity shots out of 113 shots was 10fps. The worst spread between any two consecutive shots was 7fps.

    What does stand out, is that the shot to shot readings nearly always go high, low, high, low. For example +2.8fps, -3fps, +1.6fps, -3fps and so on...

    I was curious if this is a real effect or just random chance and if it's real, what causes it.

    I have yet to compare FPS readings with pellet impact point to see if there is a strong correlation. In theory, if this was predictable and did have an effect on impact point, you could adjust for it with a slight change in point of aim, alternating high, low. Trouble is you'd have to synchronise with the changes in fps otherwise you could make the effect worse!

    Lastly, does anyone know what's involved in bringing the FPS spread down on the HW100? Is it even possible? Is a shot to shot variation of 3fps as good as it gets? Is what I'm measuring more to do with variation in pellets than what the mechanics of the gun are doing?
    The regulator is doing its job within reason. The spread is fine. The power fluctuation is probably indicative of an incorrectly set regulator but to be 100% sure the actual FPS read out against cylinder pressure is required. Unless you know exactly what you are doing I would leave it well alone. You have +- 1.5% variation which is nothing.
    FYI my S400 unregulated has 27 ft/s spread from 190 bar, and my Huntsman just over 20 ft/s spread. Your gun is fine.

    A.G

  12. #12
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    Thanks!

    Thanks guys, some interesting thoughts there and leaving the internals alone is probably good advice!

    Regarding my measurements, my Crony was hooked to my laptop, so I was rattling through the mags fairly quickly.


    So given that I'm unlikely to improve the pellet velocity spread, is there anything else I should be looking at on the gun to improve grouping at longer ranges? (50 to 100M)

    The new barrel shoots most pellets well, but the usual suspects group marginally better (AA/JSB).

    I get 14 shot groups of 25mm at 50M, 50mm at 75M and 75mm at 100M.

    This might just be as good as it gets with an HW100 of course! I know it can be an awful lot worse... it was with the original barrel...

  13. #13
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    ..... hmm

    Is this leading up to a sales pitch??
    . . . Please INDICATE when overtaking cyclists !!

  14. #14
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    Quote Originally Posted by GrahamHenderson View Post
    Is this leading up to a sales pitch??
    Curses, foiled again!




    Sell my HW? Never...

    I get very attached to my guns!

  15. #15
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    Quote Originally Posted by RichardinDorset View Post
    Thanks guys, some interesting thoughts there and leaving the internals alone is probably good advice!

    Regarding my measurements, my Crony was hooked to my laptop, so I was rattling through the mags fairly quickly.


    So given that I'm unlikely to improve the pellet velocity spread, is there anything else I should be looking at on the gun to improve grouping at longer ranges? (50 to 100M)

    The new barrel shoots most pellets well, but the usual suspects group marginally better (AA/JSB).

    I get 14 shot groups of 25mm at 50M, 50mm at 75M and 75mm at 100M.

    This might just be as good as it gets with an HW100 of course! I know it can be an awful lot worse... it was with the original barrel...
    Wash the factory grease off the hammer/shuttle mechanism. This will improve the shot to shot consistency and cold weather performance. You do not need to dismantle the gunas it can be done with the gun out of stock and with the end cap removed. Spary as much of the Napiers air rifle oil in there as it taks to do the job, let it drain offand replace the end cap and the mechanism is already lubricated. Spray more of the same oil in there from time to time to keep it luricated. I use Napiers air gun oil as it is kind to the O rings.
    Your group sizes are fine, beyond 60 yarsd and with a sub 12 air rifle it is anyones guess how the gun would group but your's are fine.
    One more point, when target shooting use the single shot adapter. HW 100 regulator takes a bit of time after each shot to settle so if you fire off one after the other, chances are that you'd be firing before the pressure is stablised, single shot adapter will slow you down and give time for the Reg to settle.

    A.G
    Last edited by lensman57; 24-01-2017 at 01:46 PM.

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