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Thread: Cast psi calculator

  1. #1
    Boolit Master
    sutherpride59's Avatar
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    Cast psi calculator

    Without specific load data is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data? I know this isn’t most important thing in the world But it would be nice to be able to guesstimate how much psi is going to be on my cast bullet based off a jacketed data.

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    Boolit Master Rcmaveric's Avatar
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    Richard Lee's modern reloader 2nd edition has a chapter on estimating pressures from some of their load data when listed.

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  3. #3
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    Quote Originally Posted by sutherpride59 View Post
    Without specific load data is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data? .......
    No there isn't,
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  4. #4
    Boolit Master
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    Hey Larry is back! Welcome back Larry! Yah that’s just a chart showing how much psi the bullet can take of that powder at a certain bhn. It’s a good reference but doesn’t really provide what I’m looking for. I’m just curious if there is a formula to guesstimate the pressure based off a known recipe.

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    Boolit Master GhostHawk's Avatar
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    I suspect too many variables for that to work.

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    Quote Originally Posted by GhostHawk View Post
    I suspect too many variables for that to work.
    Correct.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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    Boolit Master
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    Would Quick Load provide any information on pressures?
    My Anchor is holding fast!

  8. #8
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    The OPs question was;

    is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data?

    Quick Load is different. QL can give a fairly close estimate IF all the requested data is input correctly. Leaving data out, estimating data and inputting incorrect data will seriously negate the accuracy of QL to estimate pressure.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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    Boolit Man fivefang's Avatar
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    Hi Larry, in the late 50's I did not have a Chrony, but shot my Ruger .44 mag. with the 215 gr. Thompson GC. bullet over 27.5 gr.Herc. 2400, back then I wanted to duplicate the factory load, did I come close? & thank you for alof the past comment's , Fivefang

  10. #10
    Boolit Master


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    Be a couple months before I can answer that question. Haven't tested 2400 under that bullet but actually have it on my "to do" list for this fall.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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    Boolit Master
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    When these questions come up, I usually think about a comment the editor (Glen Latham, I think) of the Cast Bullet Association's "The Fouling Shot" made in an article or editorial twenty-five or so years ago.

    I don't recall the exact words, but someone, perhaps the author, might. The editor mentioned that the softest bullet fired at the highest velocity that doesn't cause leading will usually be the most accurate (probably for that bullet in that rifle). I hope I didn't alter the meaning of the author's message with my poor memory, but I believe there is much truth in the statement. Using the largest diameter bullet that will permit a loaded cartridge to chamber without difficulty may be another important factor.

    Formulas and computer programs likely have a place in the way of rough guidance or shortcutting some labor, but physically trying something still has merit.

  12. #12
    Boolit Master
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    The question has been answered. No.

    A shower thought or two as I read this thread.

    Bearing surface, alloy, lube, bore condition and heat treatment all will affect the actual final maximum pressure.

    Even changing from one jacketed bullet to another invokes the "reduce 10% and work back up" instruction that all to many of us ignore.
    My isotope lead page: http://fellingfamily.net/isolead/

  13. #13
    Boolit Master
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    extensive experimentation has revealed the empirical correlation of 3 x 480 x Brinell Hardness Number (BHN) (or more simply, 1440 x BHN) as an estimate of the minimum peak pressure required for bullet obturation
    http://www.lasc.us/FryxellCBAlloyObturation.htm
    Regards
    John

  14. #14
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    What relevance does that formula have to the OPs question?
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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    Lol because that formula was the main reason I was asking in the first place lol.

  16. #16
    Boolit Master
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    I don’t see much point to the formula if there is no way to get an idea of what your pressure is going to be with a load.

  17. #17
    Boolit Master Rcmaveric's Avatar
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    You can roughly calculate with Richard Lee's formula from his reloading manual. Its simple math as you as adjust the load max of powder by 1 grain you muliply the max load pressure by what ever it says like example .983. You can make a table for it. The down side is that if the load is for jacket bullets it will have a different pressure for cast because of the less resistance of the lead, but if you seat into the lands you going to cause a pressure spike and the pressure can be much high. I have done it and found loads for BLC-2 and 4064. Now if richard lees load data is for a cast bullet it will get you closer in the ball park. So if you are using jacketed load data for cast then the estimation is a loose stretch. Aslong as you start low and work up while keeping in the guidance of reduction limit it is safe.

    QL is a better way of estimating pressures and velocity. I am normaly 25 fps fast on my chrono than what QL tells me.

    However the PSI limits is not hard set rule of thumb. If your bullet fits it can be shot softer.

    While i do beleive that the lead has pressure and force limits. I dont think the pressures we estimate are the limit. There is more at play than simply PSI and torque. I still start light and will go over what i estimated. You never know what might work and worst thing thay will happen is i clean some leading out of my gun. I let the bullet tell me how it wants to be shot.

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  18. #18
    Boolit Master Rcmaveric's Avatar
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    Slap a gas check on a bullet and you just changed its pressure limit also. Those lead pressure estimation dont take into account a gas check. Still can be used though.

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  19. #19
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    Quote Originally Posted by Rcmaveric View Post
    Slap a gas check on a bullet and you just changed its pressure limit also. Those lead pressure estimation dont take into account a gas check. Still can be used though.

    Sent from my SM-G925T using Tapatalk
    Nor does the formula take into account the alloy used. The formula is based on the pressure needed to obturate lead.

    Many of us shoot cast bullets well above the "failure" level that formula prescribes.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  20. #20
    Boolit Master Rcmaveric's Avatar
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    Quote Originally Posted by Larry Gibson View Post
    Nor does the formula take into account the alloy used. The formula is based on the pressure needed to obturate lead.

    Many of us shoot cast bullets well above the "failure" level that formula prescribes.
    Agreed. Some times, with the way I think, I need a starting point though. Thats a good safe starting point to work up a load.

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    "Speak softly and carry a big stick; you will go far."
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check