Optimal Accuracy Barrel Length - 6.5 x 47 Lapua?

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by Phil3, Nov 28, 2018.

  1. bsekf

    bsekf

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    Don't want to argue, looking for information. I understand using a long barrel to keep bullets supersonic at long range. BUT, if long barrels are more accurate why don't the BR guys use them? In my limited experience, both barrels I have shortened to 20-22 inches, shot better????? Just seems to me as if a short fat barrel is easier to drill a straight hole in and has more stable harmonics.

    Bill
     
  2. mikegaiz

    mikegaiz Stay frosty, my friend. Silver $$ Contributor

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    How far are you planning to shoot accurately? BR only shoot 300 yds. max. Velocity and BC are very important past 300. look at the weight bullets the BR guys are shooting (light). They will be very affected by wind and distance.
     
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  3. DennisH

    DennisH Life Time NRA member Gold $$ Contributor

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    Absolutely AGREE!

    Several of us who had "tac" drivers always had our barrels "set back", and we all retained our original barrel accuracy! Sure, we added around 1,200 to 1,500 rounds down the tube, it was worth the $150 to set them back.

    300 yard BenchRest shooter usually like the bullets around the 80 grain weight area, and also use 14 to 17 twist barrels.

    FWIW, Dennis
     
  4. bsekf

    bsekf

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    As I understand it, bullet flight gets interupted when going through the speed of sound, roughly 1150 fps, so lets call it 1200. So the theory is to keep the bullet above 1200fps all the way to the target for the best accuracy. Does the speed above 1200fps make a difference? Don't have the tables handy... but it seems to me as if a 20 inch 6.5x47L will keep a 130 -140 bullet supersonic beyond 1000 yards.

    AND, Just seems to me as if a short fat barrel is easier to drill a straight hole in and has more stable harmonics. Nobody addressed this brilliant statement!

    I am just trying to gather information........ after 70 years of shooting, I am beginnig to realize how little I know!

    Bill
     
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  5. EBaker

    EBaker

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    Well, I have a 20 inch .308 that I use in a modified 1000k match not B/R more like FTR. I use an AE-30 Suppressor on the rifle. It shoots easily to 1K and beyond with pointed 175 SMK. Based on that, I built a 20 inch 6.5x47 knowing the 6.5 bullets fly better than the .308 bullets. Haven't shot it yet cuz my stock from McMillan just arrived on Wednesday. Now, I'm not talking B/R accuracy but the .308 will shoot MOA or better if I do my part. I hope to find the same accuracy or better with the new rifle as it will be a hunting rifle that I shoot occasionally out to 1K.
     
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  6. Steelnecktie

    Steelnecktie

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    I have a 20” 6.5x47 shooting 130gr @ 2750. It is very accurate, but not what I would go compete long range with from a rest or bench. I’d say 28” will get you the extra horsepower you need, anything under 28” and you’re sacrificing MV. Anything over 28” your gaining weight and maybe a few FPS.
    If you’re shooting 600-1000yds, the length of barrel is not going to be the reason you can’t hit X ring.
     
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  7. Bart B.

    Bart B.

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    I don't think a perfectly straight hole in a barrel matters much. The bore curves at different fixed frequencies while bullets go through it.

    All barrels resonate and harmonic frequencies are fixed and very stable from shot to shot as long as their shape is not changed. A valid test would be both barrels, same chamber, in the same rifle so only the barrels would be compared.
     
    Last edited: Dec 3, 2018
  8. 6MT

    6MT

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    My x47 has a 26" tube. With 139gr bullets, I get just over 2900fps with a medium charge weight.

    fwiw
     
  9. abersfelderami

    abersfelderami

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    at the target?
    Good question, You should ask that question in the ballistics board.
     
  10. Zero333

    Zero333 Silver $$ Contributor

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    Bullet flight path is true and predictable up to Mach 1.2 (around 1,350'ish yards), then it enters the "transonic" zone where some bullets can become unstable and start flying unpredictably.
    Some bullets go through the transonic zone with ease and once they become subsonic their flight path is stable once again.
     
  11. MagnumManiac

    MagnumManiac

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    There is NO CORRELATION between accuracy and barrel LENGTH.
    A good barrel can be short or long, it makes no difference.
    A thick barrel on the other hand is generally more accurate than a very thin barrel.
    The reasons are as Bart B stipulates above, barrels ‘whip around’ as bullets travel through them, the thinner the barrel walls, the more whip that is generated.

    Zero333,
    The transonic zone is when a bullet goes from supersonic to subsonic, it is this transonic ‘zone’ that ‘buffets’ a bullet which MAY cause it to yaw, this doesn’t happen every time, even with the SAME bullet.
    Atmospheric condition, altitude, humidity and air density all play a part, not just the speed transition.

    Cheers.
     
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  12. mikeeg02

    mikeeg02 Michael Glantz Gold $$ Contributor

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    I dont think that's a true statement. If a rifle is in tune, it's in tune.

    At the second day of the world open this year, I shot a medium palma barrelled, 12# silhouette rifle in heavy class, just to see what it did on paper before the ridgway championship. And why not do it in match conditions.

    Shot a ten shot 4.8" group. Naturally got beaten by .030" or something like that. Because every time I shoot small at williamsport, someone gets me by that magnitude. I sure got them talking, since it was a 12# class rifle shooting with the 100# er's. But I'm not sure contour has much to do with accuracy.

    And if you read lilja's documention, a straight 1.25" barrel has more whip then a heavy varmint of the same finish length.
     
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  13. MagnumManiac

    MagnumManiac

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    Rifle tuning has nothing to do with my statement.
    It is very difficult to keep a thin barrel cool enough to keep it from walking shots.
    I’m not talking about light match barrels, I’m talking Soda straw barrel like those on mountain rifles.
    I have seen very few that can hold 10 shots in the same group as they heat up, this is the definition of what’s accurate or not.

    Cheers.
     
  14. Bart B.

    Bart B.

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    Why?

    A skinny barrel vibrates as repeatable as a fat one.
     
    Last edited: Dec 3, 2018
  15. Bart B.

    Bart B.

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    I don't think any barrel gets hot enough to walk shots fired every 15 to 20 seconds. If properly stress relieved and fit to the receiver.

    Those skinny M14NM barrels never walked shots shot 24 times in 50 seconds
     
  16. mikeeg02

    mikeeg02 Michael Glantz Gold $$ Contributor

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    If a rifle is out of tune, its not accurate. That is independent of any taper.
     
  17. fivering1

    fivering1

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    Magnum Maniac:
    Before making absolute statements, you might read the article written about work done at "The Houston Warehouse". It is worth the time.
     
  18. Bart B.

    Bart B.

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    ...was done without a tuner, wasn't it? Betcha loads were adjusted to group in the low zeros.

    30 and 32 inch skinny barrels shooting 30 caliber 155 grain bullets have tested sub half MOA at long range.
     
  19. MagnumManiac

    MagnumManiac

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    When did I mention taper had anything to do with accuracy?

    I also never said skinny barrels are inaccurate, you all read into what you think you read.

    I stand by what I said, try shooting soda straw barrels in 3 shot groups, then try 5 shots and then 10 shots. A 10 shot group fired with a 15 second delay between shots will have the barrel so hot at the end of the string you would not be able to touch it. For example, a 25-06 shot this way will burn your hand by the 6th round, and that is in a magnum contour barrel.

    It’s all good when you READ an article and it is somehow gospel, but if I mention a generalisation, I am wrong regardless of the fact that I HAVE tested this theory, and NO, not all barrels resonate the SAME.
    All barrels resonate, but they definitely do NOT resonate at the same frequency when one is larger in diameter than another.

    Cheers.
     
  20. mikeeg02

    mikeeg02 Michael Glantz Gold $$ Contributor

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    People have told me I can be a little thick between the ears, so Ill try to explain the way I read what you wrote.

    This is what caught my interest. And in that context, I dont believe it to be true. You havent until this point stated pencil thin, nor stated that your testing shows that after they start to heat up, somewhere in a ten shot string, they start to walk their POI. Your "thick barrel" vs "very thin barrel" and my "thick barrel" vs "very thin barrel" concepts appear to vary.

    Now you have clarified "pencil thin" which to me has more meaning and I would say were on the same page as to understanding what you meant. But now you are defining accuracy to a rifles ability to hold ten shots. (Or effectively staying in tune for 10 shots) Which is along the lines of what I said, about the rifle staying in tune. And at this time I used the inappropriate word "taper" when in reality what I should have said/meant was "contour".

    You just said thicker barrels are more accurate then skinny barrels.........

    And that we definitely agree on.

    And I am not trying to start a pissing contest, just honestly trying to convey how I, and possibly others read what you wrote. Since I dont personally know you, or how you get your points across, sometimes things get lost in text.

    I apologize to you, and the others for mucking up the thread.
     

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