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Thread: Cast psi calculator

  1. #21
    Boolit Master


    Larry Gibson's Avatar
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    Note also the Fryxell/Lee formula is intended to determine the psi at which "obturation" begins. It does not determine the psi of any "load". Fryxell was also referencing bullets in revolvers needing to obturate to seal the cylinder throats. The formula does not reference calculation of a loads psi.....hence my questioning the relevance.

    BTW; the formula says my 30 XCB cast of #2 alloy (WQd) with a BHN OF 22 should obturate at 31,680 psi.....yet at 2900 fps pushed at a measured psi of 49-50,000 psi recovered bullets and excellent accuracy show no sign of obturation.......or alloy failure.
    Larry Gibson

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  2. #22
    Boolit Master
    sutherpride59's Avatar
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    Exactly how do you tell if obturation has occcured in a recovered bullet? I just thought it was a concept and the best way to tell is at what bhn your bullets get the best accuracy? It took me a while with my 45!but I found my most accurate bhn was 11 with my uspsa loads. I just figured this was when the obturation was occurring.

  3. #23
    Boolit Master
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    Telling what occurred in the barrel is really challenging unless you have a budget for equipment that dwarfs the GDP of many nations.

    Which is why we ultimately rely on accuracy to tell us what is going on. It really is the only thing that matters in our little hobby.

    And, while elastic and plastic deformation ranges and pressure can inform why a given load in a given gun may or may not be accurate, they don't matter much given the relatively simple formula that works 99% of the time.

    Make sure you bullets fit. Slug that bore and size .0005"-.001" over the measured value.

    Start softer than the internet will tell you. Bullet too hard causes more guys issues than bullet too soft. And, leading from soft lead is easier to get out IMHO.

    Reduce 10% and work up. This is the part that starts to really feel like work if you actually do it. Five shots isn't going to tell you. Fifty starts to give you a clue. And that gets worse as the gun gets more fancy.

    Finally, detailed records. We have all been there. Got the range, fired ten 5 shot groups that grouped .0000001" even taken together. Ammo ran perfectly in our gun. There was nothing downrange too small for us to hit with that bullet and load. Come home on cloud-9 that we have the magic recipe. Only to find that it was mystery alloy #6, no idea the pot temp, quenched or not or final hardness of the bullets. Can't remember how I sized them or which lube I put in them. And what primer was it again?

    I love a good scholarly article as much as the next guy...Usually more in most gun groups. But at the end of the day, the steps to finding a good load don't require us to actually know the PSI of our load.
    My isotope lead page: http://fellingfamily.net/isolead/

  4. #24
    Boolit Master fredj338's Avatar
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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? 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.
    In a word, no. Generally a lead bullet at the same powder charge as jacketed will have a bit higher pressures IMO.
    EVERY GOOD SHOOTER NEEDS TO BE A HANDLOADER.
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  5. #25
    Boolit Master fredj338's Avatar
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    Quote Originally Posted by mdi View Post
    Would Quick Load provide any information on pressures?
    Too many bullet variables I suspect.
    EVERY GOOD SHOOTER NEEDS TO BE A HANDLOADER.
    NRA Cert. Inst. Met. Reloading & Basic Pistol

  6. #26
    Boolit Master

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    Won't it vary per different alloy??

    Shiloh
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  7. #27
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    Quote Originally Posted by Shiloh View Post
    Won't it vary per different alloy??

    Shiloh

    I’m sure it would but I just their might be a formula that took all that into account. Maybe I should just start emailing the powder companies if I’m truly curious about it.

  8. #28
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    Min and Max psi would be calculated from a bullets BHN. So yes and no. Alloy content doesn't really matter but the actually BHN does. The math does not take into account how antimony aides in obturation and how tin resists obturation. But these numbers and math are all therotical.
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  9. #29
    Boolit Master
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    I go with Larry Gibson stated. too many things will change from what one things.So there is really no way with out have some other information. It is not only the powder and alloy that is used but also the gun that it is used in also.Also the twist of the rifle.
    Life Member of NRA,NTA,DAV ,ITA. Also member of FTA,CBA

  10. #30
    Boolit Master


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    Quote Originally Posted by Rcmaveric View Post
    Min and Max psi would be calculated from a bullets BHN. So yes and no. Alloy content doesn't really matter but the actually BHN does. The math does not take into account how antimony aides in obturation and how tin resists obturation. But these numbers and math are all therotical.
    Isn't that a little backwards?
    Larry Gibson

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

  11. #31
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    Yup you got those two backwards bud lol. Antimony is brittle tin is very flexible.

  12. #32
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    Quote Originally Posted by sutherpride59 View Post
    Yup you got those two backwards bud lol. Antimony is brittle tin is very flexible.
    That's the characteristics it has on target. Under pressure it acts a bit different. That's why swaged bullets have antimony and no tin. Antimony is good for the lead under pressure. The long chains break and help the solid lead flow under pressure. Tin resist that extrusion under pressure and is why it is not in jacketed bullets. Maybe it makes a difference when fire, maybe it doesn't. Its all theory and speculation.
    "Speak softly and carry a big stick; you will go far."
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