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Thread: Hatsan .25 cal AT44S-10 Long Mods

  1. #11
    Senior Member SeanMP's Avatar
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    Ain't that the truth
    Sean

  2. #12
    Moderator rsterne's Avatar
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    Barrrel and breech correction are next on deck.... might have to drill the transfer port a whisker at the same time.... Since the valve ended up at 0.180" after I streamlined it, if there is room I'll take the transfer port and barrel out to the same size.... Epoxy between the valve screws after that (and separate, I'm curious too)....

    Pretty amazing what a bit of tweaking can do.... Like you said, nothing serious here, really just "blueprinting" and tuning....

    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. #13
    Moderator rsterne's Avatar
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    Well, today was kinda wierd.... I took the rifle all apart and matched up all the ports to smooth and maximize the flow.... I ended up with a 0.180" valve top port, 0.183" transfer port, 0.185" through the breech, and a 0.187" barrel port.... I polished the barrel with some bore paste and stuck everything back together and gained a whopping 6 fps (0.5 FPE) for my trouble.... but at least it didn't use any more air, so the efficiency was a solid 1.20 FPE/CI.... Basically all the ports downstream of the valve are as big and smooth as I can go.... By now I figure the choke point is the valve seat itself.... It looks like this....



    There was a spare supplied with the parts that came with the gun, and it measures 0.171" ID, less the area of the 0.100" stem.... so the equivalvent area is the same as a hole measuring 0.139" (the same size as a stock Disco transfer port).... This is obviously a lot smaller than the rest of my ports.... I figured if I ruined the seat I had a backup, so I knocked it out of the valve and measured it.... and found that the hole in it was even smaller than the spare, it only measured 0.163" ID.... I mounted it in the lathe, and using my number drills, one at a time, slowly took it all the way to 0.187".... the same size as the ports (but still less area because of the stem).... The throat area is now the equivalent of a 0.158" hole, 50% larger area than the one I took out.... There is enough meat to drill the hole out to about 0.200", and I can thin the stem down to 0.090", and match the throat area to the area of the rest of my ports if I need to.... However, I know that if I make the valve too big, the hammer may not open it.... so I stopped at 3/16".... stuck the gun back together and shot some more strings....

    WOW!.... What a shocker.... I still had the hammer preload at 7 turns out, hoping that it would have enough oomph to knock open the larger valve at 200 bar.... Well, the first shot over the Chrony was 990 fps, then 1010, and it peaked at 1023 fps before falling back to 983 at shot 15.... Drilling out that valve seat gained me 75 fps and 8 FPE.... and the hammer still worked !!! .... I dialed the preload down to 6 turns, and then down to 5, and the gun was still shooting way stronger than before.... I set the preload back to 7 turns out and shot a string with H&N Baracudas and EunJin Domes.... Here are the results....



    The dotted black lines on the graph are from the first string today, JSB Kings at 7 turns out, before I drilled out the valve seat.... That was the most power up until today.... The red pressure line can be used for all the pellets at 7 turns preload.... Here is a summary of the results:

    25.4 gr. JSB King: 1023 fps (59.0 FPE) max.
    1009 fps (57.5 FPE) average for 15 shots @ 1.06 FPE/CI

    30.9 gr. H&N Baracuda: 957 fps (62.9 FPE) max.
    944 fps (61.1 FPE) average for 15 shots @ 1.13 FPE/CI

    35.2 gr. EunJin Domed: 915 fps (65.5 FPE) max.
    899 fps (63.2 FPE) average for 15 shots @ 1.17 FPE/CI

    That's a 9-10 FPE gain over yesterday.... The shot count is a few short of the 18 (two full clips) that I want.... but my power goal of 50-60 FPE has certainly been achieved.... and by enough margin I am confident that I can get an 18 shot string in the 950 fps range with any pellet from 25-31 gr., and that includes all the ones with a decent BC....

    It's been quite a day.... Using JB Weld on the groove in the valve will have to wait, the tubes I have are so old they are hard as a rock.... Tuesday (after the holidays) strangely seems a long way off.... but I'll enjoy the weekend knowing I've accomplished my goal with this rifle....

    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

  4. #14
    Senior Member sholo's Avatar
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    WOW!
    Wicked numbers your getting, Bob. That rig is turning into quite the beast indeed. I'm continually amazed at how much power can be obtained from opening things up by such small amounts.

    At those velocities in a 1/4 bore, it must be loud as a mother...!

    Todd
    Todd

    Don't sweat the petty things, and don't pet the sweatty things!

  5. #15
    Senior Member SeanMP's Avatar
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    Holy F***

    You've got an off the shelf 25 cal flirting with the transonic barrier. NICE!

    And enough power to blow marmots into next week
    Sean

  6. #16
    Member Gippeto's Avatar
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    Quote Originally Posted by SeanMP View Post
    Holy F***

    You've got an off the shelf 25 cal flirting with the transonic barrier. NICE!

    And enough power to blow marmots into next week
    I just cannot put it any better....X2

    Bloody well done Bob!

    Al

  7. #17
    Moderator rsterne's Avatar
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    Thanks for the accolades, guys!.... much appreciated.... I'm pretty sure with a lighter pellet it would go supsersonic, but really, who cares.... Baracudas in the mid 900s are plently, and I'll likely have to detune it a bit if it's preferred fodder is the JSB Kings.... I wonder how long it will be before JSB bring out a heavier pellet in .25 cal?.... You know, something I can't figure out.... This gun is NOT that loud compared to others I have at comparable power levels.... maybe the air splitter?... EDIT: Nawwwwwww.... I figured it out.... my other guns are all running lower pressures.... therefore a longer valve opening and a higher residual pressure at the muzzle.... No magic there I guess....

    One thing I noticed is that with improving the flow, particularly with opening up the valve throat.... the bell-curves are becoming "peakier".... I've seen that before, but the one that surprised me was the Kings at 5 turns preload.... The fill pressure dropped to 170 bar (normal) but there were still only 15 shots within 4%.... I would have expected more as the gun was "detuned".... I'm thinking that I may have to restrict the transfer port slightly to get to my 18 shots I want.... Maybe just putting a stock transfer port back in will be enough?.... I won't do anything until next week when I fill the groove in the valve with JB Weld though....

    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. #18
    Senior Member SeanMP's Avatar
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    How big is the transfer port?
    Sean

  9. #19
    Moderator rsterne's Avatar
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    Stock 0.171".... now 0.183".... Probably not enough smaller to do what I need, but Dan thinks he might have one so I'll get him to send it when I get a backup complete valve (which he has in stock - $50).... He seems to have a pretty good supply of spares for the Hatsans, which is great to see.... If Fastenal would ever ship my Teflon rod I could probably just make one from that and eliminate the two tiny O-rings.... The stock TP has a 1mm section O-ring riding in a shoulder on each end to seal it.... Nice attention to detail.... I could always duplicate the factory setup with a smaller hole, of course....

    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

  10. #20
    Moderator rsterne's Avatar
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    Just a photo of the valve with the groove filled with JB Weld.... The idea is to take up the extra volume in between the valve seat and the pellet to help keep the pressure up in the first part of the pulse....



    Testing later tonight, time permitting....

    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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