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Thread: slow twist poly barrels

  1. #1
    Join Date
    Feb 2017
    Posts
    4

    slow twist poly barrels

    I know theres regular twist poly barrels 1 in 17.7
    but has any got experience with slower twist rates than this in poly barrels. like...
    1in 27 or 1 in 36

    what has your experience been when using jsb or air arms 10.3 and 13.4
    and did you mess around with the fps.

    I feel there isint enough barrels out there offered in slow twist.. after all arnt they more accurate at long range..like 50 yards and over.

  2. #2
    Join Date
    Jul 2009
    Location
    San Antonio, TX - Flathead Lake, MT
    Posts
    183
    Newfound Wolf:

    Twist ratio is directly related to then length and mass of the projectile and very important, the distance at which the projectile is going to be shot at...Have you ever heard or found that some barrels suck at 25 Meters but shoot very well at 50 Meters or the opposite where a barrel shoots outstanding at 25 Meters but no so at 50 or more meters?

    In airguns there is one very important issue: The pellet is stabilized by rotation (Twist) but the Diabolo effect is to some point more important...TR's used for firearms or projectiles that are not Diabolo shaped do not fully apply to our regular pellets and what this means is that airgun pellets are mainly stabilized by DRAG then stabilization might be improved by rotation. After the DRAG stabilizing effect these TR's become less important (but necessary) and have a larger sweet spot compared to powder burning barrels where precise TR's are vital for most accuracy...

    Answering to your specific question:
    Yes, there has been some testing (that I know) with twists up to 40:1 where accuracy with 13.4's sucked, then some other people tested 1:36 and 1:32 with similar or mixed results. In general those very slow TR's were accurate at short BR distances but pellet fussy (lighter pellets) and not so accurate at 50-65 meters...The idea behind a Polygon or a 2-3 groove MI barrel (Minimum Invasive) is to minimize the Magnus effect, improve BC's, buck the wind better, etc.. Yes, MI's and Polygons have proven that they are more precise and cope better with the wind compared to other rifling profiles, but this benefit has its limitations/trade offs, mainly distance as mentioned above (as you slow down the TR)...
    Having said this, WL opted for a TR that would provide excellent short range accuracy with good distance performance...Much testing was done in this area so if you ask me I wouldn't waste my time discovering the black thread and will take whatever this factory offers...The second part of your question and about shooting 10.3's with these barrel profiles....There are mixed results, some polygons with the same TR shoot them well and others simply don't and slower twists tend to be the worst performers for lighter than 13.4 gr. weights.

    Now...There are some other other Polygon TR's currently in use by manufacturers who custom order their barrels...This fact is confusing because you may find that a 24:1 barrel shoots very precise (13.4's) but so do some 26:1 but then I can show you 17.7 TR Polygons that will shoot consistent 250's...What I am trying to say is: Don't be deceived by the TR of an outstanding barrel and believe that its ratio is responsible for 100% of its accuracy, most likely that barrel is shooting outstandingly because it is very STRAIGHT and has a GOOD BORE and not because of the particular profile or TR.

    If any doubt I can give you 2 examples in the US, different barrel profiles but same results: Chasdicapua (Grants Pass Oregon in the USA) has one of the most accurate WL standard .177 Polygons out there in his RAW TM-1000, the good thing is that both: Shooter and barrel are outstanding and you are not surprised when Chas shoots a 250, you are surprised when he doesn't!...I believe he shot a 1499 shooting a 9 on the 150th bull ...Think about it: He shot 149 tens before he shot a 9

    Then I have a Shilen Ratchet in a Steyr LV that shoots very similar...There are no other .177 Shilen air barrels out there to compare it because Ed fabricated this barrel specifically for doing some lab testing and he was not into airgun barrels...The TR in this barrel goes way out of whatever standards the industry has set and ratchet barrels are by no means MI's... Being what it is, this is one of the most accurate Light Varmint BR guns currently shooting in the US BR circuit, it shoots outstanding with anything from 7.9's to 8.4's, 10.3's and 13.4's and it is not pellet fussy and its accuracy goes to 60+ Meters (60 is the max distance tested)....If anything, it only needs a better shooter...I don't shoot indoors, but when outdoors if I do my part and watch those flags, this gun will shoot consistent 248 -250's

    Regards,

    AZ
    Last edited by AZUARO; 06-23-2018 at 02:16 PM.

  3. #3
    Join Date
    Feb 2017
    Posts
    4
    I have both lw 12 grove and a lw poly........I think the 12g lw is 1in16 and the poly is 1 in 17.6
    and my gun a raw bm500mk2 shoots 10.3s 915 fps
    and the 13.4s 805 fps as straight from the factory.

    ive noted better accuracy with my poly with the above pellets tuned too 20 to 30 fps less..i turned down the hs tension.


    my accuracy is just womderful with the 13,4s up too 50 yards.. then after that that accuracy really drops off very quickly.
    at 60 yards the groups open up to almost double..

    as for the 10.3s I haven't done much testing with those yet.

    and as for the lw 12grove barrel..... seems like the poly barrel is almost always more accurate no matter what distance...most of the time

  4. #4
    Join Date
    Feb 2017
    Posts
    4

    fast twist barrels

    so fast twist pellets are better for long heavy pellets and slow twist is better for shorter lighter pellets. is this a correct statement?

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