Optimal Velocity for JSB .177 16gr out of LW Polygonal barrel

Forums Pellets, Projectiles, Slugs, & Ammo Optimal Velocity for JSB .177 16gr out of LW Polygonal barrel

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    chasdicapua
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    What speeds are folks finding good results with this pellet at?  I remember a post by Aaron that the .22 cylindrical JSB’s need to be shot fast (above 925) in order to be accurate. Just wondering if that applied to the .177 cylindrical pellets.

    My TM 1000 is shooting the 16’s at 700 and the 13’s at 770 and the 13’s are definitely more accurate, which leads me to believe the 16’s would be more accurate with some more oomph. How much more though? That’s my question. 

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    Prouzy
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    Certainly could be some generalities to be made, however I would never discard potential. Ive found that some shoot ever better slower, when not accurate at faster velocities. Why? Barrel diameter, twist rate, etc??? There are a few discussions regarding this on GTA, but take a look at post #2 on this thread: http://www.gatewaytoairguns.org/GTA/index.php?topic=118462.msg1153180#msg1153180

    The greatest velocity I could achieve was just over 700fps with that set up but for only a couple shots before dramatic drop in velocity.  So my 5 shot group was like 675fps for 5 shots using the .22 33gr JSB. I dont know what possessed me to even try this, as I bought those to shoot in my Sumatra and Condor. Twenty-yards went so well I push it to 40yd. I posted two of the groups, but they were all like that.  I was so surprised and having so much fun (just dumbfounded by this little HPA QB78) I put hundreds down th barrel that day. 

    Then just recently, I took that rifle out again to try some others, as I prepare some targets for my new adventure, heavy .177 long range. So I was shooting the 25gr .22 JSB the exact same as the 33gr.  I had actually tuned it for the Baracuda Hunter, but was getting occasional flyers so went to the 25 gr JSB. Its shoots these at around 720fps. So this is my go to, as I want to hit a but harder out to 40yd (tested 15gr and 18gr as well). 

    Long story long, I think you can shoot them a little slower with success.  My guess is, more to do with the barrel, as mentioned eg twist, land/groove, choke to shoot more cylindrical projectiles. For example, look at the Sumatras and of course many slug shooter can be quite accurate shooting cylindricals at lower velocities as well.  I ordered the heaviest H&N other than Piledriver as well as the JSB 16 .177 and hope I have something more to add after this weekend. 

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    aa_limited
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    my air wolf shots the .177 16 grain jsb at low power 620 and hi power at 730 fps.
    ​jsb 13.4 lw power 700, hi power at 800 fps

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    Percula
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    In my Thomas BR I shot the 16gr at about 880fps and have BR accuracy with them.

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    chasdicapua
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    Thanks Percula, that’s what I thought might be the case. But, how to get the TM 1000 shooting them that fast?

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    aa_limited
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    change the reg pressure as well as hammer spring?

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    John_in_Ma
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    My S500 with factory prts/tune was shooting them at 870fps through a LW barrel(standard rifling) and while not benchrest accurate, were very close at 25yd.

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    chasdicapua
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    I’m aware of what actually has to be done (reg. adjust and hammer spring increase). Thing is, I want to be able to shoot the 16 gr pellets at that 880 bench rest  accuracy and still be able to turn down the power to sub 20 fpe for field target shooting without tearing the gun apart every time to adjust the regulator. (Not that I’ve ever done that even once!) I’m going to call Martin and see if its possible to have the gun retrofited with some kind of power adjuster. I see the draw of the Thomas rifles now! I really don’t want to have a second gun just for 50 yard shooting. 

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    aa_limited
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    can you let us know on here what martin says about getting yr raw to shoot the 16 grains at 880.
    ​I too am very interested in getting  my raw to shoot at 880 to as well.

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    aa_limited
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    what is the main reasn why u want to go with .177 16 g and  is there any reason why you choose 880 fps to run them at.
    ​are you thinkning 880 fps is the most accurate speed to push them at?

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    Percula
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    “aa_limited”what is the main reasn why u want to go with .177 16 g and  is there any reason why you choose 880 fps to run them at.
    ​are you thinkning 880 fps is the most accurate speed to push them at?

    
Don’t make generalizations. Just because the optimal speed in one rifle does NOT mean it will be the optimal speed in another rifle. There are many factors, and as I tried to point out to you before, the barrels ordered by the manufactures are unique to the manufactures specs. A LW poly barrel on a Thoams is NOT the same barrel as you would get on a RAW BM500. It’s not just the barrel either, everything that makes a rifle accurate will have an effect. Finding the optimal speed and pellet for YOUR rifle will take time and work. While you may get a good idea where to start looking for your optimal settings by comparing to the same model rifle as you have or one that has the “same” barrel doesn’t them that they will be the same.

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    chasdicapua
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    AA, I want to use the 16 g pellets for 50 Metere shooting. Just figuring the heavier weight will buck the wind better. The 880 fps is what Percula posted in shooting them out of his Thomas. Also, from reading posts, it seems like the cylindrical pellets have better accuracy with a higher fps. 

    Today I turned up the power adjuster on my TM 1000. The 13 g’s were shooting at 770 fps the way the gun came. This is with the hammer spring adjustment right in the middle. I got it up to 815 – 820 (45 – 50 fps increase) before the ES and SD started to increase. So, I’m thinking, if I can’t have the rifle retrofitted with a power adjuster, I’ll just do one increase on the regulator to get the 13 g’s up to 870 fps with the hammer spring set in the middle. Then I can turn down the hammer spring 45 – 50 fps to get it back down to 820 fps (just under 20 fpe for field target), or I can crank it up the other direction 45 – 50 fps to get it shooting them at 915-920 fps.  The 16 g’s shoot 70 fps slower in my rifle, so that would put them at 845-850 fps. That might be fast enough for optimal accuracy.  And as Percula said, I’ll need to experiment with the various FPS to see where my rifle shoots them the best. 

    Just trying to have one gun that will be optimal for 25M, 50M and field target shooting. I will report what Martin has to say. 

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    chasdicapua
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    AA, spoke with Martin today. He said that the rifles can’t be retrofitted with a power adjuster. He also didn’t have a sense of how fast the BM/TM could push the 16 g pellets. Every rifle is different. So, we’ll just need to experiment. I’ll have to say the HS adjustment is very accessible and easy to use. I’ll just do what I mentioned in my post above and find the optimum fps for each pellet.  Have fun experimenting!

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