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Thread: Pressure Question GC/PB

  1. #21
    Boolit Grand Master Bazoo's Avatar
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    I think that gas checks would cause an increase in pressure. I expect the percentage of pressure increase to grow with the gas check load when it moves from a reduced load into a full charge load.

    A gas check design bullet without check vs a plain base bullet of the same design I expect would be nearly identical, with the plain base bullet having a slight increase in pressure due to larger driving band surface.

    Thank you Larry for the testing, and thanks for all those that will contribute bullets, time and knowledge to this. It is a furtherment of the understanding of our craft and hobby.

  2. #22
    Boolit Buddy mr surveyor's Avatar
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    Quote Originally Posted by Bazoo View Post
    I think that gas checks would cause an increase in pressure. I expect the percentage of pressure increase to grow with the gas check load when it moves from a reduced load into a full charge load.

    A gas check design bullet without check vs a plain base bullet of the same design I expect would be nearly identical, with the plain base bullet having a slight increase in pressure due to larger driving band surface.

    Thank you Larry for the testing, and thanks for all those that will contribute bullets, time and knowledge to this. It is a furtherment of the understanding of our craft and hobby.

    Yep, that is exactly what it's all about!


    jd

  3. #23
    Boolit Master
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    Yesterday, I tested boolits from my new NOE 311-127-FN.

    4 cavity, 2 PB and 2 GC.

    All details of the load identical, except, of course,
    one set with GC, other set with PB.

    POI for GC was 2 inches higher than PB at
    approx 50 yards.

    Certainly NOT SCIENTIFIC, but an observation
    that seems to fit in this thread.

  4. #24
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    TCLouis's Avatar
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    Hopefully we will get some pressure and precision data out of Larry's gracious help.
    Unlike others in my one attempt I found leaving the GC off lead to significant increase in group size.
    That may well be a boolit to bore diameter issue also.
    So many things can be hidden as to the real reason that one gets a certain result.
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  5. #25
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    Rcmaveric's Avatar
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    I wonder if different gas check materials and designs would change any thing. Like the hornady short copper cups compared to homemade taller aluminum/copper checks.

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  6. #26
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    Ross Seyfried wrote an article titled "Ultimate Cast Handgun Bullets" in Oct of 1993. Among other things, he addressed the Pressure/Velocity of two cast bullets, one plain base and one gas checked. He had two identical 44 caliber, 305gr cast bullet molds cut, one plain base and one GC.

    He had Hodgdon's laboratory test the loaded ammo which was 21.9gr H110, CCI 350, Fed cases, with the following results.

    Gas Check -- 33,300 CUP, 1,383 fps
    Plain Base -- 38,200 CUP, 1,346 fps

    I double checked the results and yes, the GC load was faster at less pressure.

    Would copy the results, but can't figure out how to work with PDF file article.


    FWIW,

    Paul

  7. #27
    Boolit Grand Master Bazoo's Avatar
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    Paul, that is very interesting, thank you for posting.

  8. #28
    Boolit Grand Master

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    Quote Originally Posted by Paul105 View Post
    Ross Seyfried wrote an article titled "Ultimate Cast Handgun Bullets" in Oct of 1993. Among other things, he addressed the Pressure/Velocity of two cast bullets, one plain base and one gas checked. He had two identical 44 caliber, 305gr cast bullet molds cut, one plain base and one GC.

    He had Hodgdon's laboratory test the loaded ammo which was 21.9gr H110, CCI 350, Fed cases, with the following results.

    Gas Check -- 33,300 CUP, 1,383 fps
    Plain Base -- 38,200 CUP, 1,346 fps

    I double checked the results and yes, the GC load was faster at less pressure.

    Would copy the results, but can't figure out how to work with PDF file article.


    FWIW,

    Paul

    I’d love to see if Larry’s results reflect this as well. I guess the question is, why?

  9. #29
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    doc

    OBTURATION?
    Last edited by TCLouis; 09-20-2018 at 09:35 PM.
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  10. #30
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    Plain Base -- 38,200 CUP, 1,346 fps
    That's a lot of pressure on a plain base boolit, I wonder what alloy he used...and what hardness?
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  11. #31
    Boolit Master
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    Quote Originally Posted by JonB_in_Glencoe View Post
    That's a lot of pressure on a plain base boolit, I wonder what alloy he used...and what hardness?
    That Seyfried load is very similar (in fact a scosh less powder) to my full-power 44 mag load I use in my Redhawk, though my plain-based is a 280 grainer. Water-dropped ww's and I am not a good enough shot to detect a difference in accuracy between the 280 grain PB and my 300 grain GC boolits, so shoot the PB one in the revolver. A Rossi lever gets the GC boolit. Velocity somewhat north of 1300 fps from the revolver: shot a couple cow elk with the load but quit using it for elk because of failure to make exit except on a pure broad-side shot.

    I'll be most interested in seeing Larry's results. Thanks for doing this fellows!

  12. #32
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    I don't know about pressure but...I had Fred Leeth of Pioneer Products make a couple of nose-pour molds that are identical in shape & weight except for the gas-check shank. These are in .22 for my Hornet rifle. Now concerning pure accuracy..NOT velocity..the only difference between the gas-checked one & the plain-base was .3 of a grain of H4227..the gas checked requiring the "heaver" load.

  13. #33
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    Interesting..............
    JMHO-YMMV
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    Gary D. Peek

  14. #34
    Boolit Buddy Old Coot's Avatar
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    You all realize of course that a plain base bullet of the same design as one with a gas check will weigh more than the gas check bullet. Depending on the caliber it could weigh as much as eight grains more (for the plain base in say 45 or 50 cal. bullet). This could explain the rise in pressure for the same load in both plain base and gas check.

  15. #35
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    Quote Originally Posted by TCLouis View Post
    doc

    OBTURATION?
    I think that is the key element.
    The unexamined life is not worth living....Socrates
    Pain, is just weakness leaving the body....USMC
    Fast is fine, but accuracy is FINAL!....Wyatt Earp

  16. #36
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    Got the 30 XCB bullets, GC and PB, in from Time Killer....they look real good. Will be 3+ weeks before I can test as a mule deer hunt with old friends is calling me away.......

    I'll test them in the 30-30 cartridge at probably 1200 - 1400 fps with a faster powder such as Unique and at 1700 - 1800 fps with probably 2400.

    Not sure what I'll use in the 32 H&R yet, still cogitating......
    Larry Gibson

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

  17. #37
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    While you’re at it, why not add a plain base powder coated to see how it compares ?

  18. #38
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    Was reading through an old article written by Keith himself. He was discussing his favorite loads in a G&A article. His claim was GC were useless in Pistol bullets and raise pressures 3-5K and don’t allow the bullet tonobturate and fit.

  19. #39
    Boolit Grand Master


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    Got the bullets sized and lubed and the GC put on the GC'd bullets. Going to test 8 shot strings (18 test strings) in 3 rifles; 30-30, 308W and 30-06. Will test 3 different powders in each rifle with each style of bullet; Unique, 2400 and RL7. That is 144 bullets of each; GC'd and PB'd with just enough bullets left over for sighters/foulers. Maybe that won't give a definitive answer (to some anyway) but it should give a very strong indication.
    Larry Gibson

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

  20. #40
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    Strong work Larry!

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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