Cast bullets create higher pressure?

Discussion in 'Reloading' started by dgang, Jan 18, 2020.

  1. dgang

    dgang

    Messages:
    19
    Likes Received:
    6
    Joined:
    Oct 18, 2000
    Location:
    colo. springs, co 80911
    Just perusing 2005 Alliant Reloading Guide for .357 Mag. cast bullets and found some data I don't understand.(not an uncommon state) They give 7.8 gr. of Unique for 158 gr. JSP @ 1280 FPS, developing 33,200 PSI. The same data states 6.8 gr. of Unique for a 158 gr. cast LSWC @ 1295 FPS but with a higher pressure of 33,900 PSI. I can understand the difference in the amount of powder and velocities, but fail to understand why the cast bullet with less powder has higher pressure. Any help out there?
    Thanks in advance and good shooting' to ya.
     
    ithaca_deerslayer likes this.
  2. Sechott

    Sechott

    Messages:
    2,619
    Likes Received:
    4,785
    Joined:
    Apr 24, 2012
    Location:
    WV
    The lead seals much better than copper jackets.
     
    fredj338 likes this.

  3. dgang

    dgang

    Messages:
    19
    Likes Received:
    6
    Joined:
    Oct 18, 2000
    Location:
    colo. springs, co 80911
    So the lead deforms quicker and blocks the bore. Got it. Thanks
     
  4. Sechott

    Sechott

    Messages:
    2,619
    Likes Received:
    4,785
    Joined:
    Apr 24, 2012
    Location:
    WV
    The copper will bridge the grooves, while the lead will conform or swage tighter inside the grooves. Less gas and pressure will be allowed to escape.
     
    ithaca_deerslayer and fredj338 like this.
  5. Taterhead

    Taterhead Nightshade

    Messages:
    5,675
    Likes Received:
    2,427
    Joined:
    Dec 13, 2008
    Location:
    Boise
  6. geo57

    geo57

    Messages:
    863
    Likes Received:
    620
    Joined:
    Jan 9, 2010
    Location:
    Nebraska
    FWIW, current data from Alliant says that 7.7 grs. of Unique under a 158 gr. Speer GDHP in .357 mag cases yields 1040 FPS from a 10" test barrel. Sierra gives very similar .357 mag results in that 7.7 grs of Unique under their 158 gr. JHC yields 1050 FPS from a 4 " barrel. For a light .357 mag load I load 7.0 grs of Unique under a bulk 158 gr. and get an average of 950 FPS from 4" barrels.

    Lots of discrepancy in this case between the 2005 and current Alliant data. I have no real explanation for it. I acknowledge that different bullets, seating depths, bearing surfaces , etc. can make differences but in this case the difference is a lot. I hesitate to say that Alliant's 2005 data was wrong but based on what they say now, what Sierra says, what I and others have discovered using the same components it would appear to suggest the stated 2005 velocity was questionable.
     
    Last edited: Jan 19, 2020
  7. dgang

    dgang

    Messages:
    19
    Likes Received:
    6
    Joined:
    Oct 18, 2000
    Location:
    colo. springs, co 80911
    In speaking to others and from what is posted here, it seems that a cast bullet will quickly obturate in the barrel, quicker and more completely that a jacketed bullet, and cause over pressure by sealing off the gases before the bullet leaves the barrel. Seems sensible to me. Alliant has revised their load data for handgun rounds , usually by posting more powder and less velocities. When asked, they said new testing was responsible. Thanks for your interest. P.S.. and thanks for the link.
     
  8. fredj338

    fredj338

    Messages:
    31,949
    Likes Received:
    10,896
    Joined:
    Dec 22, 2004
    Location:
    so.cal.
    A jacketed bullet diesnt obturate or bump up at all. So any anomoly in the bbl & you get gas bliw by. Gas blow by is a reduction in gas pressure. Throw on most cast bullets are also at least 0.001" larger in dia, higher pressure.
     
  9. George Kaplan

    George Kaplan emeritus

    Messages:
    1,526
    Likes Received:
    2,015
    Joined:
    Dec 27, 2015
    I'm still confused, even more so after reading all 13 pages of the link.

    The Speer manual warns of NOT using 158 grain jacketed bullets (.38 SPL) as the bullets may not exit the barrel.
     
  10. dgang

    dgang

    Messages:
    19
    Likes Received:
    6
    Joined:
    Oct 18, 2000
    Location:
    colo. springs, co 80911
    I agree, it does seem to contradict what is posted. Seems to be an exception to every rule. maybe the lower pressure of a .38 not effecting the bullet base?
     
    Last edited: Jan 19, 2020
  11. fredj338

    fredj338

    Messages:
    31,949
    Likes Received:
    10,896
    Joined:
    Dec 22, 2004
    Location:
    so.cal.
    That is because jacketed bullets are not as malleable as lead so tryining to drive one at low pressure Its going to slow down faster & maybe stick. Barrel length mattesr here because of friction. In a 2" barrel, pretty hard to stick a bullet. In a 6" bbl far easier in a low pressure load.
     
    Last edited: Jan 20, 2020
  12. George Kaplan

    George Kaplan emeritus

    Messages:
    1,526
    Likes Received:
    2,015
    Joined:
    Dec 27, 2015
    fredj338, I love you like a brother. Your knowledge of reloading is unparalleled and you're always willing to help but damn, I wish you would take a moment to spell check every so often! What the hell is, "Barrel length mattes hete yoobevause of friction"? :ladiesman: It makes it harder to learn is all.
     
    dgang and Taterhead like this.
  13. jmorris

    jmorris

    Messages:
    2,989
    Likes Received:
    1,623
    Joined:
    Apr 13, 2006
    Barrel length matters because of friction?

    A bullet that might make it out of a 2” barrel might get stuck in a 26”. Even more likely if it’s a jacketed bullet vs lead or coated.

    This is the reason rifle shooters, going for sub sonic loads generally start high and work down. No fun beating bullets out of barrels.
     
    George Kaplan likes this.
  14. George Kaplan

    George Kaplan emeritus

    Messages:
    1,526
    Likes Received:
    2,015
    Joined:
    Dec 27, 2015
    Thank you. That makes sense. I can usually figure out what he is saying but that one had me spinning.
     
  15. fredj338

    fredj338

    Messages:
    31,949
    Likes Received:
    10,896
    Joined:
    Dec 22, 2004
    Location:
    so.cal.
    Yeah its a problem but I am not in English class anymore.
     
    ithaca_deerslayer and dgang like this.
  16. 9x45

    9x45 Millennium Member

    Messages:
    6,103
    Likes Received:
    3,846
    Joined:
    Jan 31, 1999
    Location:
    Southern California
    What he said was " Barrel length mattesr here because of friction" Reloader speak, barrel length matters here because of friction. Same as fasterer powdesr with heavyy bulest causs higher presuress. Faster powder, with heavy bullets, causes higher pressures. So it may make it out of a 2" J frame, but not in a 16" cowboy lever rifle... But SASS only allows lead, cast, coated, moly or poly, HiTek and the requirement is a minimum velocity of 600 fps.
     
    George Kaplan likes this.
  17. fredj338

    fredj338

    Messages:
    31,949
    Likes Received:
    10,896
    Joined:
    Dec 22, 2004
    Location:
    so.cal.
    A cast bullet will almost make it 1/2 way down a 4" barrel with just a primer. A jacketed will make it into the rifling & stop. I can pound a lubed lead bullet thru a 4" bbl pretty easily. A jacketed bullet is a nearly impossible because of friction & it isn't very malleable. Even if you lube the jacketed bullet, the round jacket doesn't deform easily.
     
  18. George Kaplan

    George Kaplan emeritus

    Messages:
    1,526
    Likes Received:
    2,015
    Joined:
    Dec 27, 2015
    You just summed up 13 pages of the thread in the link above in one paragraph.
     
    fredj338 likes this.