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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

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

  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
    sqlbullet's Avatar
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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 isnít 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.
    NRA Cert. Inst. Met. Reloading & Basic Pistol

  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

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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