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Thread: Accuracy and bullet transit time

  1. #1

    Accuracy and bullet transit time

    I have an accurate load in my 308 with a 150gr sierra. Thinking of trying 165gr. I have started playing with quickload so was wondering would the accurate transit time with the 165 be the same as the 150 i.e. Is the accurate transit time rifle specific or bullet specific?

    cheers

    BE

  2. #2
    sorry i don't know feller but i use the same in pro hunter it ticks all the box's for me, i'd be interested myself if you get a result ,

  3. #3
    Quote Originally Posted by big ears View Post
    I have an accurate load in my 308 with a 150gr sierra. Thinking of trying 165gr. I have started playing with quickload so was wondering would the accurate transit time with the 165 be the same as the 150 i.e. Is the accurate transit time rifle specific or bullet specific?

    cheers



    BE
    By 'transit time' you mean time of flight?~MUir

  4. #4
    Sorry for not being clear, I mean barrel transit time. The question is whether this is the constant that makes the round accurate despite the weight of the bullet?

  5. #5
    Hi BE

    What is behind your thinking of moving away from 150grn if it is so accurate?

    Martin

  6. #6
    More stopping power at range. Planning a trip to Scotland

  7. #7
    Big ears, put Quickload away and get out shooting, it will f**k up your mind and have you worrying about things that bare little relevence to what you are trying to achieve in the field

    Ian.
    Last edited by Whitebeard; 19-07-2014 at 22:22.

  8. #8
    What you planning to shoot at what kind of range that a 150grn wont do???

  9. #9
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    There was an article on this in Airgun world oddly enough. A specific projectile will generally be accurate if it leaves the muzzle whilst the barrel is at the maximum displacement ( in either the positive or negative direction) from its resting position. This is because the barrel with vibrate with simple harmonic motion when the shot is fired. Towards the maximum displacement the acceleration of the barrel due to this movement is tending towards 0 and so it has the least effect on the path travelled by the round. The fact that the barrel will pause very briefly before returning in the opposite direction (like a pendulum in a grandfather clock) will also reduce the effect caused by slight differences in projectile weight or propellant efficiency. You should in theory be ale to 'tune' your barrel to work with a specific round by the addition of weight to the free floating section of barrel so that this effect occurs for a different projectile speed and mass. There is no reason why this effect shouldn't occur in firearms as well as air rifles, after all the physics is the same, its just that the magnitude of the values increases. However, to achieve any reasonable gain in accuracy is extremely difficult and so just finding a round that the barrel likes is rather simpler. In terms of transit time it depends on the charge behind the round, but the heavier projectile should take longer (all else being equal) to exit the barrel as it will take longer to accelerate ( more inertia) and it will travel more slowly (muzzle velocity decreases as round mass increases in general). Both may be accurate if they both fall on maximum displacements, but not necessarily the same one if that makes sense. You can't really tell until you try it and as for whether it is even worth changing, well I'm not really qualified to say...

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