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Thread: Bullet weight, twist and velocity

  1. #1

    Bullet weight, twist and velocity

    If I use a heavy for twist bullet will it run slower than optimum through my barrel?

    I've a .243 ten twist. Sako 100gr factory loads should have an approx. muzzle velocity of 905m/s. That's the claim on the box.

    With a moderator on I clocked three of these for an average of 818 m/s. They were consistent at +/- 3m/s.

    I know that 100gr in a ten twist is heavy and not optimal for stability and accuracy, but had not considered the impact on muzzle velocity.

    Or is this all voodoo?
    I never make the same mistake twice.

    I make it five or six times.

    Just to be sure.


  2. #2
    What barrel length is your rifle (vs the length of rifle used to produce the figures on thevammo box)?

  3. #3
    22 1/2 inch barrel on my rifle, no idea of the test rifle used.
    I never make the same mistake twice.

    I make it five or six times.

    Just to be sure.


  4. #4

  5. #5
    Quote Originally Posted by jcampbellsmith View Post
    i think the appropriate response these days is OMG and WTF.
    Id expected a much greater variation due to twist.
    Now trying to get my head around the difference between manufacturer claimed velocity and actual.
    Thanks. I think?
    I never make the same mistake twice.

    I make it five or six times.

    Just to be sure.


  6. #6
    Quote Originally Posted by JockStalk View Post
    If I use a heavy for twist bullet will it run slower than optimum through my barrel?

    I've a .243 ten twist. Sako 100gr factory loads should have an approx. muzzle velocity of 905m/s. That's the claim on the box.

    With a moderator on I clocked three of these for an average of 818 m/s. They were consistent at +/- 3m/s.

    I know that 100gr in a ten twist is heavy and not optimal for stability and accuracy, but had not considered the impact on muzzle velocity.

    Or is this all voodoo?
    Maybe you know something the riflemakers don't, as this is the standard .243 twist designed for 100gr and below.

    The MV of the Sako 100gr Gamehead (Sierra) quoted is from a 60cm barrel. Your batch is slow, and only making 1600 ft/lbs, so power-wise it's really a .22-250.

    These are the only conclusions I can draw.
    If I'm going to be accused of it then it's just as well I did it.

  7. #7
    Given the nature of my question, I guess I don't need to point out that I am not presuming I know more than a riflemaker.

    So batches can vary that much, to give a 10% variation from mean velocity?

    Didn't expect that. Glad they are not in the aircraft components business.
    I never make the same mistake twice.

    I make it five or six times.

    Just to be sure.


  8. #8
    Well it ain't nuts n bolts...

    You will quickly find out that no two rifles shoot the same ammunition with the same 'performance'.
    You are confusing length with weight regarding twist, length is the defining factor.
    Twist rate will not make much measurable difference to velocity whereas the chamber volume, for example, will produce quite noticeable variations in velocity.
    Your 10% variation is in the tested barrel that the figures are quoted from?
    A young man who isn't a socialist hasn't got a heart; an old man who is a socialist hasn't got a head.
    I have summat for sale; here's the M̶i̶d̶w̶a̶y̶ Brownells UK price... effin jokers.
    "The .30-'06 is unstable at close range" - Ahahahahhahh!


  9. #9
    Thanks Sauer, so it's not twist - and it's not the load so much either.
    Lots to learn!
    I never make the same mistake twice.

    I make it five or six times.

    Just to be sure.


  10. #10
    Quote Originally Posted by JockStalk View Post
    Thanks Sauer, so it's not twist - and it's not the load so much either.
    Lots to learn!
    Another point to consider is the accuracy of your chronograph. Regards JCS

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