.25 Marauder low power tune

Forums PCP Airguns .25 Marauder low power tune

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    ajshoots
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    I started working on a used .25 I just received yesterday. Bought it as a project gun and decided to start with a low power tune. I have never tried to tune one for low power and high shot count. I always opt for horsepower.

    After full teardown and honing the airtube, I removed the lawyer spring and set the trigger for a single stage pull of 7oz. I always throw away the stock depinger as I feel they are worthless and just take up volume.

    I did open the gauge block and increased volume and flow of the valve. Changed hammer spring, but left everything else stock.

    From a 3000psi fill, my first string was 48 shots at 800fps with JSB kings. Not to bad of a start. Hope to play with tuning later today and see how much improvement I can make.

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    bill_dd97
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    Awesome, my current tune on my .25 Marauder is giving me 32 shots from 3000psi to 2000psi at 820fps with AA 25.4gr. The rifle is still stock with 3x 211 o-rings. I need to work on it a bit more as I’m getting a spread in the 30s.

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    fr8rbum747
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    ajshoots – I adjusted one of my 25 Marauders down to increase shot count and smooth out the shot curve using a Lane Regulator after cleaning up all the snags in the main air tube with a ball hone and removing the manometer block.  By adjusting the regulator up and down I was able to then look for a decent balance of hammer spring and throw. The stock or slightly modified air valve became the problem with the 25 cal.  The larger caliber just requires an X amount of air down the tube.  It was an interesting visit to physics 101.  At around 650 fps and 110 / 120 BAR (regulator set point) I hit the most consistency with a shot count around 48 with 3000 psi fill.  After that it would fall off the regulator and numbers fell off rapidly.  Those were my best numbers and I had to fiddle with the regulator adjustments which ate a lot of time and air.  
    3000 psi charge 
    110 BAR – 1600psi / 48 shots / 650 fps / 9 es
    120 BAR – 1750psi / 40 shots / 658 fps / 5 es
    If you already have 48 on the shot count at 800 I would like to see your shot curve and consistent shot count.
    Oh yea all shooting was with JSB / 25.39..I am sure you can do much better with your skills.  I tore the rifle down with new seals, Hill valve and regulator set to 135 BAR. Went back to more familiar shooting because it got boring shooting at those speeds and loss of range.
    Interested in how your project turns out..

      

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    fsa46
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    AJ, what distance were you shooting, how was the accuracy and what psi did you shoot down to ?

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    ajshoots
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    I have yet to shoot any groups. Gun doesn’t even have a scope on it yet. I do all my chrono work in my shop 3ft from the muzzle into my indoor backstop.

    Fr8rbum, 48 shots were from 3000psi down to about 1700psi. Just under 5% ES. If I start at 2800psi and only shoot 40 shots, the ES drops to 3%.

    I am just experimenting with some ideas right now. If you saw the valve and hammer spring, you would never think this gun would do what it is doing.

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    DJBriez
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    I wanted to find a happy medium between the 2 (shot count/power) with my .22 Marauder. I also wanted to  try out an FFH, to see if it would lend to that effort.
    I shot this string back in April of this year after installing the FFH……There are a few things wrong with the string (occasional sharp hi’s/lows), but with out having really streamlined the tuning, this is what it shot, from 3000 to about 1800 psi (if I remember correctly…I forgot to log start/end psi in the software). The following just eludes to what may be REALLY possible with this low cost device.

    Bullet Weight(gr): 15.89
    Temp: 0 °F
    BP: 0.00 inHg
    # FPS FT-LBS PF
    70 838 24.78 13.32 
    69 834 24.55 13.25 
    68 836 24.66 13.28 
    67 842 25.02 13.38 
    66 847 25.32 13.46 
    65 852 25.62 13.54 
    64 845 25.20 13.43 
    63 837 24.72 13.30 
    62 846 25.26 13.44 
    61 846 25.26 13.44 
    60 846 25.26 13.44 
    59 863 26.28 13.71 
    58 862 26.22 13.70 
    57 864 26.34 13.73 
    56 859 26.04 13.65 
    55 873 26.89 13.87 
    54 872 26.83 13.86 
    53 795 22.30 12.63 
    52 874 26.96 13.89 
    51 869 26.65 13.81 
    50 850 25.50 13.51 
    49 829 24.25 13.17 
    48 836 24.66 13.28 
    47 837 24.72 13.30 
    46 793 22.19 12.60 
    45 868 26.59 13.79 
    44 887 27.76 14.09 
    43 870 26.71 13.82 
    42 857 25.92 13.62 
    41 852 25.62 13.54 
    40 862 26.22 13.70 
    39 891 28.02 14.16 
    38 857 25.92 13.62 
    37 874 26.96 13.89 
    36 841 24.96 13.36 
    35 815 23.44 12.95 
    34 866 26.47 13.76 
    33 799 22.53 12.70 
    32 819 23.67 13.01 
    31 846 25.26 13.44 
    30 871 26.77 13.84 
    29 887 27.76 14.09 
    28 846 25.26 13.44 
    27 881 27.39 14.00 
    26 836 24.66 13.28 
    25 825 24.02 13.11 
    24 885 27.64 14.06 
    23 858 25.98 13.63 
    22 897 28.39 14.25 
    21 909 29.16 14.44 
    20 862 26.22 13.70 
    19 840 24.90 13.35 
    18 697 17.14 11.08 
    17 827 24.14 13.14 
    16 805 22.87 12.79 
    15 805 22.87 12.79 
    14 813 23.32 12.92 
    13 861 26.16 13.68 
    12 885 27.64 14.06 
    11 909 29.16 14.44 
    10 837 24.72 13.30 
    9 809 23.10 12.86 
    8 857 25.92 13.62 
    7 877 27.14 13.94 
    6 853 25.68 13.55 
    5 885 27.64 14.06 
    4 848 25.38 13.47 
    3 722 18.40 11.47 
    2 868 26.59 13.79 
    1 784 21.69 12.46 
    Average: 847.0 FPS
    SD: 36.0 FPS
    Min: 697 FPS
    Max: 909 FPS
    Spread: 212 FPS
    Shot/sec: 0.1
    True MV: 847 FPS

    DJ

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    ajshoots
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    Based on how well my wife’s regulated .177 turned out after using my own SSG design, I am sure I could have great results using one on this gun. However, I want to see what I can do without using an ssg or FFH or bstaley o-rings for that matter.

    I am thinking about donating this gun to a raffle or something good of that nature. I might also keep it as a loaner gun to help gain new airgunners?

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    DJBriez
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    That’s a very noble thing to do AJ!….
    Let us know how it progresses 

    DJ

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    pbguns
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    Nice work on the .25
     

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    Jayman07770
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    Ajshoots, Can you tell us how you open the gauge block and increase flow on the valve. I like to try doing to my stock parts before buying another aftermarket block and valve. 

    Thanks in advance 

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    ajshoots
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    The gauge block can have an offset hole milled in it so that the gauge adapter threaded hole is not effected. You can also simply remove as much material as possible without ruining the threaded adapter hole.

    For the valve, there are all different things that can be done. I turned some off the stem side outer face. Bored out the inner ID for volume as well as opened up the end cap. I opened up the valve throat as well as the exhaust port. The valve spring was also changed.

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    Deleted Account

    AJ – Did you use a lighter or stiffer hammer spring?  If stiffer, was this increased spring rate accomplished because it is a shorter spring?

     

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    ajshoots
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    Stiffer hammer spring but it isn’t shorter. Actually slightly longer. My experiment is basically a gun that is using everything needed to make a high fpe gun but restricting it by transfer port and barrel port size. Curiosity is my driving force on this little project. I know from past experience that if I simply opened up the tp and barrel to .187 or larger, I would instantly have a 70+fpe gun.

    I am actually surprised at the performance. I expected it to shoot much faster with the parts I used. I am at my target speed, just didn’t expect it to get the lower speed and not waste tons of air. It is surely less efficient than it could be but learning is the goal for this project.

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    Deleted Account

    Thank you for the info.

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    spysir
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     Thanks for sharing, fun project.  I’ve used an original RWS48 in .25 for Squirrel and your marauder should work a lot better.   I keep a loaner around and think it is a great idea and usful tool for recruit new shooters.

    John

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    fr8rbum747
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    ajshoots-Most people are striving for what you have on that Marauder set up already.  Great spread (es) for both the 48 and the 40 shots (Wow) down to 1700 psi.  If the spring setup looks weird then weird is damn good.  I would guess that if the configuration looks funny then one or both of the springs have taken some sort of a set in tension. Whatever it is don’t fix it if it ain’t broke.  I know you are going to mess with it more because that is the point of the project.  What spring tensions did you start with (coil and length as well) or were they stock? 

     

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    fr8rbum747
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    DJBriez – Nice breakdown on the 22 and shot count.  If you notice the spikes in your shot count as you run up the string with the low of 697 and soon to follow high of 909,  I have found them to be caused by several things besides the law of physics of compressible gases (decreasing pressure, air density, chamber volume and air movement within the cylinder) .  I have had an audible click when reviewing recordings of my shot strings associated with the fps shift.  One or both of the springs moving on the hammer and or the air valve reseating itself between cocking and shooting the shot.  Reseating of air  valve (remember a spring of set tension handling large variations in air pressure / air volume very quickly)
    Not much you can done about either except check lubrication or sharp edges within the cylinder near the hammer and reworking the air valve itself.
    Thanks for sharing your numbers.  Hard work pays dividends, stick with it.

    Remember that audible bong when you shoot with out a de-pinger.  Well that air is in the cylinder moving at near sonic speeds at times during a shot.  The de-pinger just quiets it down.  That internal shock wave is what I am referring to on smaller diameter cylinders such as the Marauder applied to the valve seat. 

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    ajshoots
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    I am simply using a 12.5lb hammer spring with zero preload. I order these in bulk from Mcmaster Carr. They are slightly longer and larger wire diameter than stock. My thought in this is simple. I feel a free flowing valve has alot more to offer than a restricted one. You can always restrict the transfer port. The reason behind the heavy spring is simply for hammer bounce.

    I have proven in my high power guns that an anti hammer bounce device is not needed. Why? Heavy hammer springs reduce and in some cases eliminate hammer bounce. I tried multiple ssg and ffh designs on my high power guns. Non of them did anything but reduce overall power. The commonality of all these guns are the use of a heavy hammer spring. So, I wanted to try it. Seems like it is working well on this gun.

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    fr8rbum747
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    Alright.  Thanks for the comeback on the hammer spring and your experience.  Zero preload…That is interesting.
    Yea I went down that road with debounce devices from the modified hammers and dodads that simply increase wear on the cylinder or worse.  I am using some air valves that are wide open from Hill.  They look real pretty..lol…figure if I can eliminate each hurdle or introduce a constant along the chain of events then it is simply mechanics of the process of the firing cycle.  Just need to smooth out most the bumps during a chaotic event in a small space using a compressible gas. 

    Then stop, have a generous libation and pat myself on the back like nobody else has done this before….LOL..
     

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    DJBriez
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    “fr8rbum747”DJBriez – Nice breakdown on the 22 and shot count.  If you notice the spikes in your shot count as you run up the string with the low of 697 and soon to follow high of 909,  I have found them to be caused by several things besides the law of physics of compressible gases (decreasing pressure, air density, chamber volume and air movement within the cylinder) .  I have had an audible click when reviewing recordings of my shot strings associated with the fps shift.  One or both of the springs moving on the hammer and or the air valve reseating itself between cocking and shooting the shot.  Reseating of air  valve (remember a spring of set tension handling large variations in air pressure / air volume very quickly)
    Not much you can done about either except check lubrication or sharp edges within the cylinder near the hammer and reworking the air valve itself.
    Thanks for sharing your numbers.  Hard work pays dividends, stick with it.

    Remember that audible bong when you shoot with out a de-pinger.  Well that air is in the cylinder moving at near sonic speeds at times during a shot.  The de-pinger just quiets it down.  That internal shock wave is what I am referring to on smaller diameter cylinders such as the Marauder applied to the valve seat. 

    
That’s interesting stuff FR8 !…. And thank you…I like posting things about my experiences, to inspire ideas from others, to inspire me aagin!…I love how that “circle” works in this community!

    DJ

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