Is Velocity 'always' a good indication of pressure?

Discussion in 'General Discussion' started by royinidaho, Jun 12, 2005.

  1. royinidaho

    royinidaho Writers Guild

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    Is Velocity \'always\' a good indication of pressure?

    Am shooting a factory 338 Win Mag. With 74gr RL-19 and Hornady 225 interlocks velocities are 2800+. Pressures seem high as indicated by Fed-215 primers filling out towards the pocket edge and a bit of flatening of head stamp words. No increased effort to open the bolt. Neck sized and reloaded they fit right back in.

    Then there's the 75gr of RL-22 and the Sierra 250gr gameking. Pressures 'appear' quite a bit lower as indicated by the primer (edges still rounded) no head stamp deformation but, velocity is right at 2800fps. /ubbthreads/images/graemlins/confused.gif

    There must be something I don't know. /ubbthreads/images/graemlins/frown.gif
     
  2. LB

    LB Well-Known Member

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    Re: Is Velocity \'always\' a good indication of pressure?

    Not at all.

    If you are using a powder that is too fast for your case capacity and bullet weight, you might not see even normal muzzle velocity, but you might have excessive pressure.

    Good hunting. LB
     

  3. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Re: Is Velocity \'always\' a good indication of pressure?

    Roy,

    What LB says is true, but, if you are using appropriate powders you can certainly rely on velocity to keep you out of pressure problems.

    What youhave occuring though is not possible to relate to velocity comparisions because there are to many variables in your equation.

    First off, your using two different powders which will react differently in pressure and velocity.

    Also your using two different brands of bullets that will vary in jacket thickness, core hardness and baring surface length.

    Finally you are comparing differnt bullet weights. While you would imagine the heavier bullets to produce more pressure, youare using a slower powder with a softer, thinner jacketed bullet in the Sierra.

    So to answer your question, yes, for a given set of standards, velocity is a very accurate product of pressure but do not assume that it is consistant when you change so many variables.

    To be honest, try RL-22 in your 225 gr load and see what happens. I suspect it has more to do with the burn rate of the powders then anything.

    You just can not compare different powders and different bullets and different bullet weights, to many variables in the equation and they all produce different pressures curves, sometimes dramatically different.

    Good Shooting!!

    Kirby Allen(50)
     
  4. LB

    LB Well-Known Member

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    Re: Is Velocity \'always\' a good indication of pressure?

    I don't know if you may find this helpful, but it is what I do.

    When considering a new load, I search every publication I can find. What I am looking for, is highest velocity, and that usually tells me the correct powder for the combination of case capacity and bullet weight.

    In this way, I do not bother with a powder that appears max'ed out in the data, (but) the velocity is not <u>matched</u> by others I have charted.

    Therefore, I would not use R19 in a 338, if other powders are performing at a higher velocity.

    An over simplification, of course. You may be looking for other factors, the most accurate metering powder, the cheapest, the most available. Endless possibilities. But, if you approach it from the standpoint of velocity, (and you are) then you may see the value?

    This is very easy research. If (for instance) spherical powder, or temperature stable, is your choice, find one that comes closest to IMR, or vias versa. But, that is a good way of determining which powders are too fast, or too slow for your application. Which powders fit in a range of suitable propellants. This information jumps right off the page, if you are (at all) observant.

    Good hunting. LB
     
  5. goodgrouper

    goodgrouper Well-Known Member

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    Re: Is Velocity \'always\' a good indication of pressure?

    One other thing to consider which may seem too easy is the method in which you got your velo in the first place--the chronograph itself!

    I have seen <font color="blue"> HUGE </font> variations in chrono readings throughout the last several years. One chrono might read a bullet at 2800 and another chrono lined up directly behind the first chrono reads the exact same bullet at 2900! I have even seen two chronos of the same make get the exact same bullet differing 100 fps or more! Also, some of the cheaper chronos will read the same load drastically different on different days that have disimiliar lighting conditions.
    All of these things are something to consider. Bottom line, the chrono is almost more important than the gun so buy well once, cry once!
     
  6. royinidaho

    royinidaho Writers Guild

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    Re: Is Velocity \'always\' a good indication of pressure?

    gg, you wouldn't be referencing my "chrony" would you. It was given me by my kids for xmas a couple of years ago.

    I just love it. Especially when those little plastic thingers spread like quail, the sun goes behind a cloud and velocity drops off 30 or 40 fps or gets the ERR-2 thing or on and on and on...

    If its reading of 2800 when the books say 2600 should be expected I feel really good. Money well spent for a super rifle, you betcha!!!.

    Proof will be in the puddin' when I get it back shooting well enough to do a drop test.

    Like they say in the computer world. "Give a fella a program and torment him for a day. Teach him to program and torment him for life." /ubbthreads/images/graemlins/grin.gif