Transonic flight

Discussion in 'Extreme Long Range Hunting & Shooting (ELR)' started by jasent, Jun 27, 2018.

  1. jasent

    jasent Well-Known Member

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    For those of you that have had bullets survive the transonic zone and not go haywire what bullet,speed and twist where you using? Personally I have yet to find one that’s consistent. I’ve been told that the .338 300gr OTM does well.
    Planning my next build and goal is 2000 yards. Any and all experience is appreciated.
     
  2. Hoffer

    Hoffer Active Member

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    I run Berger 300OTM's. Pointed

    338LM 2575fps gets you 1070fps at 2000 yards. You can definitely run up to 2800fps.

    338 LM Imp 2915fps gets you 1310fps at 2000 yards
    These are at 3900 density altitude

    All above super accurate at 2000 yards

    If you run solids it will go 200 yards farther
     
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  3. jasent

    jasent Well-Known Member

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    338 lm imp is one I’m thinking about. How long is your barrel getting those speeds? I’m at 2200’. If I could get those 300’s over 3000 I would’nt need to worry about transonic zone
     
  4. Hoffer

    Hoffer Active Member

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    31" barrel. I could run faster, but I'm trying not to stretch my brass too much.
    338 improved is a fantastic cartridge.

    Bergers are awesome into transonic
     
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  5. rbcowboy

    rbcowboy Active Member

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    338LM in a 31” barrel is running 2890 with Rel33 and 285elds. You might get to 3000 or so with the improved but I wouldn’t count on it! I’ve had the 285’s to 2400 in my RUM but I’m pushing them 3100. Either the 285eld or 300otm will suit you fine just run them on the warm side to get your speed up as best you can! Both transition quite well into subsonic flight!
     
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  6. jasent

    jasent Well-Known Member

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    I’m now thinking I want to go with the 338/408 CheyTac
     
  7. Clearlight

    Clearlight Active Member

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    Agree the improved 338 version gets you around 3k velocity , and great performance at 2k yards .
    The bigger magnums will certainly raise your hit rate , but are quite a step up in cost to build
    and feed .
     
  8. Pro2A

    Pro2A Member

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    When going transonic....about 1325fps down, you will benefit from using Bryan Litz's Applied Ballistics Custom Drag Curves. (G7 BC curves are fine above 1325fps.....if they are accurate. Caution: Many manufacturer BCs are optimistic as they use their best BC for only one velocity point. BC varies over the entire velocity range. Hence, CDCs are the best.) These can be accessed in AB Ballistic solver found in Kestrel 5700 Elite Ballistic; Sig Kilo2400ABS, or one of several AB stand alone solvers (from $29.99 Google Play Store app; $125 AB mobile app; SB Point Mass Solver included with Applied Ballistic for Long Range Shooting book about $50; or AB Solver with complete program suite including WEZ (Weapon Employment Zone analysis about $200, etc.) These also allow specific curve truing at extended range for your specific system and DOPE.
     
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  9. jasent

    jasent Well-Known Member

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    I do use ab and do plan on getting the cdc’s, also have most of Brian’s books
     
  10. Clearlight

    Clearlight Active Member

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    Regarding Applied Ballistics CDMs , I’m running a Garmin 701 which has the entire library of
    Doppler tested BCs and CDMs included . So far with several rifles and bullets , the drag models
    have proven to be very accurate even into and through transonic . In the past regardless of
    solver , I’ve had to tweak the curve in transonic zone .

    Long story short , running a BC required separate tracks ( profiles ) for short , mid and ELR
    ranges . This years KO2M winner was doing exactly that to get solver prediction to match dope .
    I’m finding that ABs CDMs are eliminating the need for multiple tracks , or truing .

    It’s a given these days , for best transonic results , you need to spin that projectile as fast as
    practical for best subsonic performance . For EG , a buddy has a 10 twist 300 NM , mine is an
    8 twist : he is fine out to over a mile , but over that my faster twist gives more consistent
    elevation . Same brand and length barrel , same load just different twist .
     
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  11. jasent

    jasent Well-Known Member

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    I purchased the cdc’s last night for the bullets I’m shooting. Going to do a little testing today
     
  12. jasent

    jasent Well-Known Member

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    32566E91-87F4-4E48-9A54-1F956FAA0A69.jpeg Well yesterday I went out to test the custom drag curve. Took my 243. It goes sub-sonic around 1300. First round hit at 1380, missed first round hit at 1515y due to wind but then put 4 in a row on a 1.5 moa rock. Pretty impressed with that! CDC’s work
     
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  13. Clearlight

    Clearlight Active Member

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    Nice shooting , you obviously have the details squared away . 1500 is a good poke for a 6 mm .
     
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  14. Pro2A

    Pro2A Member

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    Jasent, congrats on those hits. If you have access to Bryan Litz's Applied Ballistics for Long Range Shooting book, Chapter 16: Weapon Employment Zone Analysis contains a great WEZ of the 243Win (see pg 302-306, 310-312) depicting effect of uncertainties (range, wind, rifle/ammo precision, velocity, target size) on hit probability. WEZ allows analysis of which parameter contributes the most to misses at various ranges. Standard Deviation (SD) in muzzle velocity (including velocity measurement discrepancies); range estimation error (a digital number isn't always correct); wind uncertainty (wind reading is THE ART of the system); shooter capability, etc are really critical with obtaining hits at range......even zero distance, and rifle cant become critical. Accuracy and Precision for Long Range Shooting Chapter 8: Leveling Your Sights shows how 3 degrees cant with .243 can induce horizontal error of 16.2" @ 1000yds (0.4" vertical); 41.0" (only -1.1" vertical) @ 1500yds. Human eye only discerns about 3 degrees under best conditions....before introducing optical illusions of tilted visual references, Cant gets misinterpreted as horizontal wind error and one ends up chasing their tail. Install and learn to use a good level.....every shot! Bubble is OK; ceramic ball (Accuracy 1st) is better; electronic (Send It!...down to 0.2deg....Long Range Arms, Idaho Falls, ID) is best.....IMHO. Keep ringin' 'em!!!
     
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