Velocity=Pressure?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by retiredcpo, Feb 4, 2011.

  1. retiredcpo

    retiredcpo Well-Known Member

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    OK I know I read this somewhere but not to sure if it is correct.
    Does velocity = pressure in other words
    if a Hodgen load data show a Max load of 60grs @2787 pressure 49,800cup max
    If you load is shooting at say 2600 its safe to go hotter since you are not at the 2787 maxium yet.
    Or is this way off base and you cant tell what your pressure is based on velocity.
    retiredcpo
     
  2. Mikecr

    Mikecr Well-Known Member

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    Only in a general sense.
    And it's too general to rely on.

    Barrels have a charactor of their own. Some are faster or slower for a given pressure or load.
    With this, I've never seen any real use for reloading manuals, not even in their general sense.
    Having used QuickLoad from the first available revision, I've learned that every barrel -to- load has to be calibrated. This includes powder lots.

    I trust only my case measurements as pulled from a smoking chamber, for pressure, and my Oehler chrono for velocity.
     

  3. retiredcpo

    retiredcpo Well-Known Member

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    So there is really no way of knowing what your pressure is
    you can check the visual signs flat primmers hard bolt movement ect
    for indication but you never really know exaactly
    retiredcpo
    BTW I am getting about 200 fps lower that what the manaul says I should be getting
     
  4. Forester

    Forester Well-Known Member

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    Without a lot of equipment most of us will never buy there is no way to know for sure.

    That said, if I am getting a lower than book velocity, with little or no pressure signs and a max powder charge, I don't hesitate to continue working up SLOWLY.

    If you are not pretty darn comfortable with what increased pressure starts to look and feel like then just quit when you hit book velocity or powder charge, whichever happens first.
     
  5. boomtube

    boomtube Well-Known Member

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    Well Chief, we can't get velocity without pressure but how that pressure occurs is the real controlling factor. We can get 60k psi in a .300 Win Mag with both Bullseye and H-4831 but only with the slower buring powder can we otain much velocity. Velocity comes from the burn rate almost as much as the peak pressure, meaning the longer we push the bullet the more it will accelerate.

    You don't mention the cartridge that's 200 fps slow for you, rifle or pistol, but if you mean a rifle load is that much slower than a book projection it's NOT an uncommon thing. Nor, as a practical matter, does such a loss actually mean beans in the woods and field; you can see that by checking most any velocity:trajectory chart. The difference in 200 fps is ususlly equal to being maybe 30 yards further from the game and that really doesn't make a lot of difference - if it does, get 30 yards closer! ;)

    Good job swabby, thank you.
     
  6. retiredcpo

    retiredcpo Well-Known Member

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    forester
    I dont know near as much as most here and Im just trying to wrap my head around this new chrono stuff
    I do know most of the indicatrions of pressure and may work up alittle And down alittle the onl;y thing that really matters in the end is that I can repeatly hit what I am aiming at which it can.
    the load shoots well but the ES is around 100fps and the SD is around 30fps I would like to get these numbers down alot more

    Boomtube
    The load is for a 7mm rem mag pushing 160gr accubonds
    Its not the worst one we have(numbers wise only) but its not the best.
    I actually have a300 wsm load with a ES of 30 and a SD of 9 which I think is reall good.

    I think I might play with slight charge changes .25 gr at a time see if things change much

    Also going to try placing the chrono further away it was about 15 ft but I did notice a slight movement of the screens everynow and then
    may also try more time between shots we noticed as the barrel heated up the shots got faster

    we are just learning how to use this chrono

    thanks for all the help
    retiredcpo
     
  7. boomtube

    boomtube Well-Known Member

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    "Also going to try placing the chrono further away it was about 15 ft but I did notice a slight movement of the screens"

    That shouldn't be necessary. At 15 ft., the bullet should have passed before the muzzle blast has any effect.
     
  8. retiredcpo

    retiredcpo Well-Known Member

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    that makes sense did not think about the bullet being long gone when the screens moved
    I was reading on here somewhere and it said if the screens are moving it could give false reading.
     
  9. Mikecr

    Mikecr Well-Known Member

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  10. RDM416

    RDM416 Well-Known Member

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    One other factor that has not been mentioned yet in the "velocity / pressure" question is the effect of the burn rate of the powder.

    If your powder is too fast, it will create a pressure spike early in the bullets progression down the bore, then begin to taper off. That is why using a powder that is too fast will give you pressure indications, but velocities may be low. So in that case, more pressure does not equal more velocity.

    Another way to get a pressure spike is if you have a tight neck chamber which does not allow the case neck to expand and release the bullet. This situation can give you fits with pressure signs, while at the same time producing low velocities.
     
  11. retiredcpo

    retiredcpo Well-Known Member

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    I am not seeing any signs of pressure
    Im running a max load according to hodgen
    but my vel is about 200 fps low so I thought I had read somewhere
    that it was safe to go hotter since I have not reached max Velocity yet
    but then I am aware that 200 fps is not a whole lot in the grand scale of things
    I am just trying to understand what this chrono info is telling me and what I can do to improve things
    retiredcpo