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Thread: Hatsan .25 cal AT44S-10 Long Mods

  1. #21
    Moderator rsterne's Avatar
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    Got some time this evening to do the testing of the valve with the groove filled in with JB Weld.... As expected, there was a slight gain in performance, but the efficiency has pretty much leveled out.... Here are the results....



    The interesting thing about this version is that the performance at mid-preload settings continues to improve.... The best shot strings are now happening at less preload than before.... I got 19 shots within 4% with the JSB Kings, 971-1007-968, averaging 992 fps (55.5 FPE) at 1.13 FPE/CI, filling to 200 bar and shooting down to 133 bar at 6 turns of preload.... The best strings with the H&N Baracudas and the EunJin Domes were at 6.5 and 7 turns of preload respectively, and returned 16 shots....

    I shot a few pellets at 8 turns of preload, and the velocities were peaked pretty much at 200 bar for the lighter pellets and 180 for the heaviest.... The maximums recorded were:

    25.4 gr. JSB Kings - 1046 fps - 61.7 FPE
    30.9 gr. H&N Baracudas - 982 fps - 66.2 FPE
    35.2 gr. EunJin Domes - 939 fps - 69.1 FPE
    41.7 gr. EunJin Pointed - 881 fps - 71.9 FPE

    I think there is a bit more in the gun yet, I could enlarge the valve throat a bit more and slim the stem.... and then I might have to make the inlet side of the valve breathe a bit better as well.... If I do that, I will then have to restrict the transfer port to keep the velocity under 1000 fps with the JSB Kings.... so I don't know if it's worth it....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  2. #22
    Moderator rsterne's Avatar
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    I decided to finish the job.... I drilled out the valve seat to 0.203" and thinned the stem to 0.090".... That makes the throat of the valve the same area as the valve exhaust port.... In addition, I drilled four 7/64" holes at a 20 degree angle in the inner end of the valve to allow more air to enter the valve.... This has more than doubled the inlet area, so it is now a lot easier for air to enter the valve than leave it....



    The extra holes in the inlet side should not be necessary unless the valve seat is drilled out, as the original hole was the same size as the throat, and it didn't have a stem obstructing it.... Hopefully I will find time to test again tonight.... Sorry for the slightly blurry photo....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  3. #23
    Member Dukemeister's Avatar
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    Bob, nice work. But you do realize winter doesn't start officially until December, don't you?
    I guess you will just have to find a different winter project......
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  4. #24
    Moderator rsterne's Avatar
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    Well when I bought it, I figured it would be until then before I got any time.... Fortunately, that wasn't the case.... Don't you worry about my lack of projects.... I still have a brand new (never fired) B-51 sitting here.... plus my Hayabusa, which will NEVER be finished (at least I hope not, because that will mean I ran out of ideas).... It's next version will be what Sean and I are working on, a .224 cal firing 41.5 gr. bullets high subsonic.... Then I still have .308, 9mm, .458, and .410 shotgun barrels to go on it.... See what I mean?.... Other projects that need finishing are my reversed tank versions of my 2260 and 2560 regulated HPA rifles, and I still have to fit a .25 cal barrel to my QB deluxe HPA....

    Yeah, I don't think I'll run out of projects any time soon....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  5. #25
    Moderator rsterne's Avatar
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    Got to run some strings over the Chrony tonight.... can you see the smirk on my face?.... Drilling out the valve throat and slimming the stem, combined with opening up the inlet on the valve.... gave me the highest performance I have yet achieved.... The larger valve seat required an additional turn on the hammer spring preload to overcome the extra force holdind the valve shut.... but even without doing that the performance was up, although it was at a lower pressure.... Once I went from 6 turns preload to 7, the entire 17 shot string of 25.4 gr. JSBs was over 1000 fps, peaking at 1044 (61.5 FPE)....



    I didn't bother adding more hammer preload when I shot the Baracudas and EJ Domes, so the graphs above are a direct comparison of the three pellets at the same power setting.... The 'Cudas peaked at 65.4 FPE and the EunJins at 67.5 FPE, but they would be shooting over 70 FPE had I bothered to add enough preload to bring the start of the string up to 200 bar instead of 175.... I cranked up the preload for a few shots with the EunJin Pointed 41.7 gr. pellets, and at 11 turns of preload and 190 bar I got 78.4 FPE.... I'm thinking with 12 turns, right at 200 bar, I can hit 80 FPE (for one shot)....

    This rifle has turned out to be a real beast.... I've likely got too much velocity even for the 'Cudas, but until I get the opportunity to put some lead a lot further downrange I won't know if I can get away with leaving the tune as is, or if I'll have to detune it for accuracy.... Nice problem to have, though !!!

    EDIT: I forgot to add that the efficiency for the above strings was 1.11 FPE/CI for the Kings, 1.21 FPE/CI for the 'Cudas, and 1.28 FPE/CI for the Domes.... so not only is the performance up, so is the efficiency....

    Bob
    Last edited by rsterne; Aug 09 2012 at 11:18 PM.
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  6. #26
    Senior Member SeanMP's Avatar
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    70 fpe AND 1.28fpe/ci

    Who says there is no gold at the end of a rainbow.....BRAVO!
    Sean

  7. #27
    Moderator rsterne's Avatar
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    One thing which has puzzled me about this gun is that when I dial the power back with the hammer spring preload, the shot count doesn't increase.... I decided today to fit the oversized 0.153" non-PAL valve stem into the now very much oversized ports and test it.... After doing that, I turned the stem down to 0.140" in the throat area, which is the size of the main part of the stem, and ran more tests.... Here are the results....



    It appears that the best way to tune the Hatsan is to adjust the valve stem size to adjust the power, and then use the hammer spring preload to adjust the operating pressures.... certainly if you want to get the best efficiency.... Using the best strings from the above and previous graphs, and always starting from 200 bar (or as close as possible), here are the choices I have so far with JSB King 25.4 gr. pellets.... In all cases, only those shots within 4% of the maximum velocity in the string are counted, and the average FPE for the string is stated....

    17 shots at 59.5 FPE (1027 fps) at 1.11 FPE/CI, refill at 130 bar
    19 shots at 55.4 FPE (991 fps) at 1.13 FPE/CI, refill at 133 bar
    22 shots at 51.6 FPE (957 fps) at 1.16 FPE/CI, refill at 130 bar
    25 shots at 45.6 FPE (899 fps) at 1.22 FPE/CI, refill at 133 bar
    31 shots at 43.4 FPE (877 fps) at 1.28 FPE/CI, refill at 122 bar

    Other than with the mildest tune, I have a usuable pressure range of 1000 psi, from 2900 down to 1900, and with the 43 FPE tune, that range is extended down to about 1750 psi.... Other tunes in between should be possible with the right combination of valve stem diameter and hammer preload.... Small adjustments can be made with just the preload.... I'm very pleased with the shot count and the efficiency figures I have been able to achieve with this rifle.... and I'm looking forward to doing some accuracy and pellet testing....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  8. #28
    Senior Member remtom1200's Avatar
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    Well, vacation's over, time to open up my AT44 10/22 again! I am surprised of the results from opening the valve seat bore. This is a great write-up bob, and now I will try and find a balanced combination for my shorter version in .22 cal.
    For every mile of road, there's two miles of ditch

  9. #29
    Senior Member remtom1200's Avatar
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    sorry to reply to an old thread... but what is your turn measurement on the hammer spring preload screw? Is it a 180 or 360 degree turn?
    For every mile of road, there's two miles of ditch

  10. #30
    Moderator rsterne's Avatar
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    No problem.... 1 turn is 360*....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

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