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Thread: Chamber Pressures

  1. #21
    tired of idiots vz58's Avatar
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    8mm has almost the same rim diameter as a 308 (right?)
    assuming so, then it has a force in cup of 9084
    9580 for 308
    7011 for x39

    or 29.6% greater than x39

    Now here is what I like. According to biggun the light 260 rem round would be
    7907 or 13%over the hottest x39......

    Now if you fire lighter loads (these were all the hottest) this would change
    The cases with more taper should have *slightly* higher forces than straighter wall cartridges
    Last edited by vz58; 10-25-2007 at 08:54 PM.

  2. #22
    No Hope For Me 1biggun's Avatar
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    8MM has same rim DIA as 308 correct. MY IMR b00k has the 243 and 7mm-08 win at around 50,000-51,000 average CUP. I expect the 260 to be right in line with those numbers as well.

  3. #23
    Happy Camper hcpookie's Avatar
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    OK here's a question... actually 2

    Has anyone seen or used this before? Got the link from Varmint Al's website:

    http://www.shootingsoftware.com/pressure.htm


    And...

    What we should do is find some numbers for the shear strength of some more popular metals. I mean, if the metal itself has a shear value of say 90,000 CUP, then in theory this means that even a hot .308 conversion would still be well within the capacity of the metal lugs.

    Know what I mean? I guess I'm trying to find a correlation of exactly where the computed values of caliber conversions fall on the "its going to break at this value" chart. If we can find a ballpark for the more popular metal types that would give us an idea of how close to the red line the caliber conversions fall.

    Do you think perhaps less expensive metals would be what was used for AK bolts? Or is there a "more popular" type of metal that is employed? Whenever I think tool steel, I think something like 4xxx or like 01 steel. I remember looking up either 4130 or 4340 and it was way up there near 100,000 PSI. I know PSI does not equal CUP, but it is a starting point. Where is that CUP/PSI conversion formula?
    Gunco Member #10

    http://pookieweb.net


    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
    http://pookieweb.net/pink/pink.htm

  4. #24
    Happy Camper hcpookie's Avatar
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    FYI, I found this searching... not sure if the formula was already posted:

    http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

    The formula is:

    PSI ~= -17902 + 1.51586 * CUP

    There is a strong correlation, but the relationship is not absolute.
    Last edited by hcpookie; 10-30-2007 at 11:25 AM.
    Gunco Member #10

    http://pookieweb.net


    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
    http://pookieweb.net/pink/pink.htm

  5. #25
    Gunco Maniac sjohnson's Avatar
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    "Pressure Trace" is a decent system, but you end up with relative pressures. Unless you have a calibrated load and rifle, or some way to measure CUP and correlate to the Pressure Trace reading, at best you can determing relative pressures (such as "this load is hotter than a previous load").

    That said, it's a good system that uses standard engineering tools and principles, and works very well in conjunction with chronometers and load charts.

  6. #26
    No Hope For Me 1biggun's Avatar
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    I have been considering just taking a really rusty kit and putting a junk 308 barrel on it loading up some 65,000PSI PROOF rounds and string firing it then scraping it when done. ALL THE CALCULATIONS IN THE WORLD WONT MEAN CRAP IF IT BLOWS UP IN THE REAL WORLD (Might be able to do it with super hot 7.62x39 loads). I show loads for the 308 that are as high as 61,700 (to hot IMOA for a AK bolt) if it will proof out at say 65,000 IT should be good to go for the 52,000 PSI hand loads I want to use in real life shooting. Dont manufactures use proof loads to test there designs I knjow in europe they are big on that stuff. It would only cost around $50-$75 to build up a test gun the trunion and bolt would be the only thing that would likely get damaged if it did blow. I have loaded 7.62x39 up to the point of primers starting to flatten and have had no problems yet. (DO NOT TRY THIS AT HOME YOU COULD DIE!!!) I am guessing that those rounds were at around 51,000 psi. If I recall the 5.56 nato was SAMMI limited to around 51,000.. IF your a hand loader then there are plenty of loads for all oif the 308 family of rounds well with in the confines of what some of the hoter 7.62x39 loads are. IF I recall correctly the AK round is SAMMI speced at 45,000 CUP that should equal aprox 50,000+ PSI. Does any one have a link or infor on the SAMMI specs ????? this would be a good start as to what the MAX that USA manufactured ammo would be at or under.

    I wish I could find chamber pressures on the 458 SOCOM 50 beowulf 450 bushmaster. I want to know what the bolt thrust is with the bigger rim diamiters of those rounds???

    does any one have a computer program that shows loads that are to hot for given rounds???

  7. #27
    No Hope For Me 1biggun's Avatar
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    Here is some super good INFO on the 308 VS 7.62 nato. and SAMMI stuff

    http://www.thegunzone.com/30cal.html

  8. #28
    No Hope For Me 1biggun's Avatar
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    SAMMI SPECS HERE not sure about if it is CUP OR PSI ON SOME OF THESE LOADS HOWEVER

    http://www.ramshot.com/powders/

  9. #29
    No Hope For Me 1biggun's Avatar
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    the ram shot site shows the 6.5 grendal,s hotest load at 52,000 PSI (about the same as the 7.62x51 nato) so it can be added to the list.

  10. #30
    No Hope For Me 1biggun's Avatar
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    here is were i saw the 50,000 CUP for the 7.62x39 NOT sure I would trust it but I thought I would show the link

    http://www.chuckhawks.com/7-62soviet.htm

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