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Thread: Calculating pressure ❓

  1. #1
    Boolit Bub Mandoair's Avatar
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    Calculating pressure ❓

    Donít know where to post this.

    Simply is there a calculation formula for estimating internal pressure of a load using say fps and bullet weight❓

  2. #2
    Boolit Master Wheelguns 1961's Avatar
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    Simple answer. No. There are too many variables for that. The best way to estimate pressure is with a computer program like Quickload.
    Due to the price of primers, warning shots will no longer be given!

  3. #3
    Boolit Master

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    What’s the load in question?

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    Boolit Master

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    I have interpolated some shotgun loads that way, just to get an idea. if you use the same powder and primers and load weight, given the fps from a know load and compare to my trial load fps. its very ball parkish and a strain gauge would be much better, but they are expensive.
    if you are ever being chased by a taxidermist, don't play dead

  5. #5
    Boolit Master
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    Mandoair -

    Howdy !

    Ballistician Homer Powley invented his " Powley Computer " as an aid to handloaders. He also provided a " PSI Calculator " .

    Check out: kwk.us/powley.html


    With regards,
    357Mag

  6. #6
    Boolit Bub Mandoair's Avatar
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    Thank you.

  7. #7
    Boolit Master
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    Calculating pressure involves many variables.
    Yes,, there are computer programs,, (such as Quickload) or other things like the Powley Computer mentioned,, that can offer a GENERAL idea of POTENTIAL pressures.
    But the problems arise (read blown up guns,) when PEAK pressure hits a specific spot in a firearm. That's the biggest issue that's harder to calculate without a strain gauge. And even then,, it has potential drawbacks if not placed where the peak can or might occur.

    Variables,, is the key thing here.

    Example; load 3 rounds, where the only difference is how the bullet is loaded. (1) bullet, loaded in one case w/o a crimp, to a bullet with a normal crimp, to a bullet with a heavy crimp all will have a different peak pressure point. It may not be very far apart,, but it is important,, say in a revolver,, if the peak occurs in the chamber,, vs the barrel.

    This is but one example of variables.

    The OP didn't state what kind of handload he was talking about,, so it's a wide open discussion.

    When I teach handloading,, I always stress; "Load within the guidelines of the books,, and load for accuracy. If you do that,, you will find that most often,, the upper level loads aren't necessary. Accuracy trumps power,, and often power,,if exceeded, can cause trouble."

    Loads in the manuals have been tested by the good folks at these companies,, because of LIABILITY. I prefer to not push the limits,, and I also like to keep from over-stressing a machine. And a firearm is a machine.

    Just like drag racing.
    You can buy a pair of cars,, use one for daily, normal "old lady going to church on Sundays,,," & the other one for drag racing. The drag racer will fail fairly quickly,, while the little old lady driven car will still be going good many years later.

    Now I know many folks will want to argue that their upper limits or excessive loads are fine. I just prefer to be safe & not take chances. with my guns, myself,, or gosh forbid,, anybody nearby when I'm shooting.

    So to try & figure out pressures,, if working towards a top end or excessive load,, you are hindered by variables without proper equipment to safely test these things.

  8. #8
    Boolit Bub Mandoair's Avatar
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    Quote Originally Posted by contender1 View Post
    Calculating pressure involves many variables.
    Yes,, there are computer programs,, (such as Quickload) or other things like the Powley Computer mentioned,, that can offer a GENERAL idea of POTENTIAL pressures.
    But the problems arise (read blown up guns,) when PEAK pressure hits a specific spot in a firearm. That's the biggest issue that's harder to calculate without a strain gauge. And even then,, it has potential drawbacks if not placed where the peak can or might occur.

    Variables,, is the key thing here.

    Example; load 3 rounds, where the only difference is how the bullet is loaded. (1) bullet, loaded in one case w/o a crimp, to a bullet with a normal crimp, to a bullet with a heavy crimp all will have a different peak pressure point. It may not be very far apart,, but it is important,, say in a revolver,, if the peak occurs in the chamber,, vs the barrel.

    This is but one example of variables.

    The OP didn't state what kind of handload he was talking about,, so it's a wide open discussion.

    When I teach handloading,, I always stress; "Load within the guidelines of the books,, and load for accuracy. If you do that,, you will find that most often,, the upper level loads aren't necessary. Accuracy trumps power,, and often power,,if exceeded, can cause trouble."

    Loads in the manuals have been tested by the good folks at these companies,, because of LIABILITY. I prefer to not push the limits,, and I also like to keep from over-stressing a machine. And a firearm is a machine.

    Just like drag racing.
    You can buy a pair of cars,, use one for daily, normal "old lady going to church on Sundays,,," & the other one for drag racing. The drag racer will fail fairly quickly,, while the little old lady driven car will still be going good many years later.

    Now I know many folks will want to argue that their upper limits or excessive loads are fine. I just prefer to be safe & not take chances. with my guns, myself,, or gosh forbid,, anybody nearby when I'm shooting.

    So to try & figure out pressures,, if working towards a top end or excessive load,, you are hindered by variables without proper equipment to safely test these things.

    Thanks, it is as i figured, too many variables and no real scientific formula. I am new to this foray and the more I learn the less I know!! I started last Feb. with 9mm and no chrono. Started on 10mm about Oct. with AA#5 cause I had some from a yard sale deal, no telling really how old it was. I had 1000 old but unopened cci 350 lpm primers form a friend and once fired brass from the range with no intention of measuring them just sorted by manufacture. I used data from Speer Manual #14 and Berry plated 180 gr. rnfp . I began below the start charge in the book of 8.5 , mostly because of the mag. primers, and worked up by .02 gr. to 9.5 gr. with very little crimp. Had no chrono but was going for accuracy, and stopped at 9.5 just at the Speer number and their estimate of 1116 fps. I took a 15rd. test out to the range with my brand new never used chrono along with some other loads. The learning curve of the chrono kept me from recording most of the rounds but I was seeing speeds of 1260 fps and I think more, didn't record them cause I thought the chrono was doing that. Now as I look for load data other places I see max loads listed in the 8.5 gr. Range and speeds around 1200fps.. I will attempt to upload picture from my phone latter of the primers. The cases look OK no damage, and only a couple of thousandths larger in diameter then the lighter loads. Now I am using HP-38 ,5.1 gr with more accuracy most likely because of less velocity. I'm starting to use cases all within .002" of each other not crimping, and seating for a tighter uniformity. I don't know what the pictures will show, but the primers are very flat with parallel lines and a very extruded firing pin dimple. All fired from a S A XDM 4.5” Elite. So far since Xmas it's been too cold, dark, and snowy to play with the chrono. Thanks for everyone's input.
    Last edited by Mandoair; 01-17-2022 at 03:30 PM.

  9. #9
    Boolit Bub Mandoair's Avatar
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    Last edited by Mandoair; 01-18-2022 at 12:45 PM.

  10. #10
    Boolit Master

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    Computer programs but always procede with caution. I have safely used both programs to find starting loads with unknown powders. Just remember all things equal its atill a SWAG (smart wild **** guess). Eatimate a rough max charge below max estimated pressure. Drop the charge 10% down and work up.

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