7mm Rem mag 168gr or even 180Gr tumble and inaccuracy with 8 twist barrel?

Discussion in 'Long Range Hunting & Shooting' started by Elkdeerhunter, Apr 26, 2019.


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  1. Elkdeerhunter

    Elkdeerhunter New Member

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    I was in the process of getting a 8 twist barrel for my new to shoot the berger 180 or eld 175 and was going to test the 195 bergers but then I read an article the other day in Terminal Ballistics that using the 8 twist barrel will cause accuracy issues and bullet tumbling with 168 gr bullets as well as the 180 grain bullets at longer distances, say over 500 yrds. I dont want to just have a single use barrel for the 195 as this is a hunting rig and need to shoot different bullets for different purposes although main use for this 7mm is potentially long range elk hunting, hence also testing the 195 gr as well,,,,

    Anyone have this experience using an 8 twist barrel and 7mm mag?

    Thanks for any hel

    Elkdeerhunter
     
  2. coop2564

    coop2564 Well-Known Member

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    This seems illogical, while I do not have a 8 twist it makes no sense with the bullets you mentioned that this would happen.
     
  3. sedancowboy

    sedancowboy Well-Known Member

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    I have 8 twist and absolutely no problems with 175 ELD-Xs and 195 EOLs. Diving the 175s at 3212fps. You generally can not over stablize a bullet, you might spin the jacket off.
     
  4. jebel

    jebel Well-Known Member

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    I agree with the other comments you’ve received. I’d be curious to see the article in question, if you have a link.
     
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  5. djfriesen

    djfriesen Well-Known Member

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    OP, this also seems counter intuitive to me. Can you link the article? Excessive spin could probably impact terminal performance, but in-flight stability should be un affected, short of jacket separation, as cowboy mentions.
     
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  6. BallisticsGuy

    BallisticsGuy Well-Known Member

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    As soon as someone says it'll be differently stable at longer ranges than at shorter ranges you can pretty much dismiss whatever comes before or after that. Bullets are either stable or unstable when they leave the muzzle. It's a boolean, yes or no. They will either tumble or they will not while in supersonic flight and they'll do it very early in the journey. Because the force trying to flip the bullet over is losing strength as the bullet slows down its velocity while the angular momentum that keeps it stable is relatively unchanged, hence the bullet only becomes more stable downrange. That's for pure supersonic flight only.

    What will actually happen? It'll spin the lighter bullets just a bit harder than necessary and the lightest possible bullets it'll spin entirely too hard, all which can exacerbate any mass distribution inconsistencies in the bullet leading to potentially larger groups. Notice the "can" and "potentially" in that? It means that the practical consequences are likely to very much resemble "none at all".

    You'll have what most .308 owners with 10 twist barrels have. A twist that's just fast enough for really heavy bullets, a bit excessive for mid-weight bulets and way too much light weight bullets. They're able to shoot just about anything they can stick in the case. Ask yourself, has everyone with a .308 burning 150gr pills on a 10 twist barrel had trouble? I've personally shot 500m matches with 110gr half-jacket .308 loads doing 3200 from a 10 twist barrel without issue. Sg on that is around 4. Ideal is around 1.5-ish. To get down to a 1.5 Sg on a 10 twisted .308 you need to start looking at >200gr bullets going REAL slow.

    In really small bullets like .223 and under that are super light with very light jackets you can see bullets turn to grey puffs of smoke about 15 yards out from the barrel when they're spun exceedingly hard but they're also meant to be that fragile.
     
  7. twister

    twister Well-Known Member LRH Team Member

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    you will be fine with 8 twist, both mine shoot 195's no problem.
     
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  8. preventec47

    preventec47 Member

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  9. preventec47

    preventec47 Member

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    I am surprised at how WRONG the supposed "experts" are here with their "nonsense".
    Yes indeed there are consequences of over spinning a bullet other than
    spinning the jacket off. The decrease in accuracy significance increases with distance.
    For illustration, lets assume an extreme situation. Long shot at 2500
    yards. Lets assume for simplicity you aim fifteen degrees above target.
    IF your bullet is over spun, when the bullet arrived and hits the target
    the bullet will be aiming or pointed 15 degrees off of the direction of
    travel. ie flying sideways a bit compared to the light path and still
    pointing in the original direction of aim instead of following the path of flight.
    THIS IS OVER-STABILIZATION.
    When the bullet flies sideways like this accuracy goes all to heck
    as you would imagine... especially as the bullet is spinning rapidly
    and an effect much like a curve baseball occurs causing a veer sideways
    as if there was a slight wind.
    This is the reason every barrel does not come from the factory with
    crazy fast twist. You cannot get good accuracy with a light short bullet
    in a fast twist barrel nor vice versa.
    You know where I learned all this ? I was a punter in football.
    Too much spin and the spiraling ball will not "turn over" as it comes
    down at the other end.
     
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  10. BallisticsGuy

    BallisticsGuy Well-Known Member

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    15 degrees huh... laugh. Look up Dunning-Kruger.
     
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  11. FEENIX

    FEENIX Well-Known Member

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    deer-eats-popcorn_64.gif
     
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  12. Texanjohn

    Texanjohn Well-Known Member

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    Sorry Preventec47 , but I can’t agree with your example, the bullet left the barrel spinning true to its path of flight, if it didn’t “tip down” air resistance would be higher at its base versus its tip, bullets aren’t shaped like footballs so while your theory may be true in football, I think the “experts” are correct here.
     
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  13. preventec47

    preventec47 Member

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    It doesnt matter what you agree with.
    You know what they call people who insist on remaining ignorant ?
    Go study "Principles of Artillery 101"
    If what you said is true, there would be no need for grooves in barrels, they
    would all be smooth bore. In fact some projectiles do adhere to your explanation
    and they are or can be shot from smooth bores. Tanks and Shotgun slugs as examples........ NOT modern BULLETS. If fact... you got it backwards. When impacting gel for instance, why do you think bullets swap ends ? Because the center of gravity is behind the center of friction/drag. And for the other expert who doesnt like 15 degrees, have him study english for the understanding of the expression "for clarity"
    And hey, yes some bullets are/were shaped like footballs. In the 30's there were experiments showing pointed on both ends outperformed all others but
    later testing revealed that truncating the rear point into "boattail" shape provided 90ish percent of the improvement with major improvements in practicality.
    I would not have said anything but I hate to see know-it-alls to profess they
    know it all when they dont. Here is the lesson for the expert who only thinks there
    is stabilized or not stabilized. There in fact us under stabilized, stabilized and over stabilized. That's all.
     
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  14. Jason millichamp

    Jason millichamp New Member

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    Indeed a bullet will not tumble but only swap ends. It's physics. The heavier part of the bullet will start going first when it becomes unstable and the front will follow oscillating or wagging behind the heavier part. It will look like it's going through the tartget sideways but it's just the point following the heavy part and being badly out of line. Some very heavy stable artillary projectiles when launched will impact the target at the same angle as the when launched. The tip will not follow the flight path.