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Thread: Lead bullet pressures are greater than jacket bullet pressures of the same weight

  1. #161
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    longbow

    "Larry mentions .30-30 which runs at somewhat lower pressure than .30-06 or .308 but should still be representative and again is a popular cartridge."

    I mentioned the 30-30 because a cast 170 gr bullet can be shot over the max load for 170 gr jacketed bullet w/o other variables entering in. Doing so in a .308W or 30-06 can raise those other variables.

    Sorry, but I got a little lost since I read "start low & work up." ...... trying to figure out how THAT is relevant to the question of this thread; "All things being equal do lead bullets generate more pressure than jacketed bullets?" that the OP asked in his original post.........




    .....
    Last edited by Larry Gibson; 12-29-2018 at 10:12 PM.
    Larry Gibson

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  2. #162
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    On the 375 Whelen observation. Anyone who owns WILDCAT CARTRIDGES can read Mike Petrov's whole chapter on the 400 Whelen and how WITH THE CORRECT G&H/WHELEN chamber there is never a headspace problem.

    Larry, thanks for your thread on Berdan conversions AND of course you are correct, there is no way an equivilant cast load has more pressure than jacketed. Next we'll read that a Model A has a higher compression engine than a 427 Ford side oiler !

    Tom McHale sez: "Even among bullets with the same overall weight, performance can vary widely, often as a result of friction as a bullet travels down the bore. As a simple example, it’s easier to push a soft lead bullet down the barrel than a hard copper jacketed one." Easier to push means less pressure. Try slugging a bore with a jacketed bullet !

  3. #163
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    Quote Originally Posted by Larry Gibson View Post

    I can run this test easily enough. I have on hand;

    ...


    Name your poison........

    Is no one else going to take you up on this???

    As much as I'm sure most of us here have internalized the idea that a cast boolit will produce less pressure than a j-word of the same weight all less held equal, we can hardly turn up the chance to get some number to get an idea of the magnitudes of the difference!


    Test the 30-30 and the .44, and at two charge levels for each; one nice and mild and one on the spicy side.

    Having comparative pressure data for both a pistol and a rifle cartridge at both the lower/higher end would substantially elevate the quality of this discussion and make for a great reference to point people towards in the future.

    So how about it? Don't make me beg Larry.

  4. #164
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    Might surprise some of you that in 1988 while doing a write up about his beloved 357 magnum, Skeeter Skelton stated, with all things being equal, that a plain base bullet would would create more pressure than a gas checked bullet. He went on to say that a soft cast bullet would also create more pressure than a hard cast bullet. Food for thought...

  5. #165
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    Did Skeeter have pressure transducer data to prove that or was he reading tea leaves ?

  6. #166
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    We've already determined by actual testing and measuring the pressure that PB vs GC'd bullets really doesn't make any difference pressure wise. As to "a soft cast bullet would also create more pressure than a hard cast bullet" we may just have to test that one also. I really hate to do that to Skeeter as I've always enjoyed his writings and musings but a lot of the old time writers did state what they thought was or would happen w/o any real testing. They also promulgated each others myths, old wife's tales and tea leaf readings. The writers these days along with many on forums still do the same. Given the ready availability of chronographs and even pressure testing equipment we'd expect a more serious approach to fact finding on those old promulgated myths.........

    Peregrine

    No need to beg, I'll begin loading some tests for the 30-30 and 44 magnum. Might do the 45-70 also.
    Larry Gibson

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  7. #167
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    Larry:

    Nothing wrong with .30-30 and I understand your logic. Same logic I had for the .45-70. I mention .308 or .30-06 as they are common and will produce pressures well above "normal" cast boolit pressures for "extreme" cast boolit pressure/velocity. I am thinking alloy hardness will play into this some too. If the alloy is really hard it will not obturate much if any and that would be one of the issues in bore friction with cast boolits. A soft(ish) alloy or higher pressure takes care of that.

    And I suppose a qualifier here. When I mention .45-70 I am thinking high end loads of at least Marlin 1895 level with PB boolits compared to jacketed. I used to run my 1895 and Siamese Mauser right to the top end of their respective load range with PB boolits so they were seeing high enough pressure to obturate ACWW. You have already commented on alloy hardness so I'm guessing that is covered.

    This should be interesting regardless of outcome as we should have some definitive knowledge when you are done. And thanks for taking this on.

    Longbow

  8. #168
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    The lead alloy has more "friction".......that is one of the "myths".

    Our lubed cast bullets ride the bore on a coat of lube regardless that the alloyed bullet has a much lesser friction coefficient. If we recover such fired alloy bullets that went into the barrel .001+ over groove diameter we find they are .002 - .005"+ under groove diameter after exiting. They do not "seal" the bore with bullet alloy on barrel steel contact. Ergo there is really no obturation but actually swaging down of the cast bullet instead.

    Jacketed bullets do not "ride" on a layer of lube and there is bullet jacket to barrel steel contact. Along with the fact that the jacketed bullet is much harder than a cast bullet and requires greater pressure for the rifling to engrave the jacket, for the bullet to swage down if over groove diameter and the jacketed bullet has a greater friction coefficient and is in contact with the barrel steel.......that is why the pressure is higher with a jacketed bullets using a given load all other things being equal.
    Larry Gibson

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  9. #169
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    I found this on 45 ACP, same weight bullet with cast v jacketed......https://wwpowder.com/244-2/Click image for larger version. 

Name:	45 ACP 230 gr bullets.jpg 
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    Last edited by swheeler; 12-30-2018 at 01:32 PM. Reason: add screen shot
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  10. #170
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    You will notice that both are loaded to same OAL, max charge for 230 FMJ 5.6grs and 19.7k psi, 230 Lead RN max charge 4.9 grs and 20.1k psi. Wow .7 grs more powder is a LOT in the 45 ACP case. The lead bullet is .452 dia and the jacketed std .451, makes you think about "blanket" statements doesn't it.
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  11. #171
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    Like so much I do, its not very Scientific, but a simple test should answer the question:
    Load a normal, safe, and sane load with a jacketed bullet, the same charge and similar/same weight of a cast one.
    After firing them, look at the primer. My guess is the cast load will show less 'flattening' from pressure.
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  12. #172
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    Quote Originally Posted by swheeler View Post
    You will notice that both are loaded to same OAL, max charge for 230 FMJ 5.6grs and 19.7k psi, 230 Lead RN max charge 4.9 grs and 20.1k psi. Wow .7 grs more powder is a LOT in the 45 ACP case. The lead bullet is .452 dia and the jacketed std .451, makes you think about "blanket" statements doesn't it.
    Yes the OAL is the same but the information there does not show the seating depth of either. The data does not identify the 230 gr LRN bullet either. Thus we do not know if the seating depth is the same. We do know for a fact (yes this is a "blanket statement") that seating depth affects pressure. Ergo, from that data we do not know, as stated in the OPs question if "All things being equal" applies.

    I will test with all bullets seated to the same depth because that affects the pressure and will adhere to "all things being equal"....... the cartridge OAL does not.
    Larry Gibson

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  13. #173
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    Just pointing out a tid bit, read post #14. Winger Ed you are correct that "reading primers" is not very scientific.
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  14. #174
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    Bullets of the same weight and material with different bearing lengths produce different pressures. The more bullet contact the more friction.

  15. #175
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    We've considered our boolits are riding on a film of lube. It would be interesting to note the pressure differences between a squeaky clean barrel and a properly fouled barrel on both cast and jacketed.

  16. #176
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    Quote Originally Posted by Loudenboomer View Post
    We've considered our boolits are riding on a film of lube. It would be interesting to note the pressure differences between a squeaky clean barrel and a properly fouled barrel on both cast and jacketed.
    In the last 10+ year since I've been using the Oehler M43 PBL to measure pressures among other measurements I've conducted 2,541 tests most of which were 10 shot tests. Those were tests were done with 28 different cartridges in 23 different test firearms. That amounts to 22,500 +/- rounds tested.

    I always clean the barrels after each test session so they are "squeaky clean" so to speak. While I usually fire at least 2 "foulers" prior to testing a clean barrel my observation is most often the velocity and pressure measurements of the 2 foulers out of the clean barrel fall within the ES of the 10 shot test of velocity and pressure. Also I have conducted 20+ ten shot tests over the last 10 years with a single lot of M118SB in one .308W test rifle w/o shooting any foulers out of the clean barrel. Again, the measured velocity and psi have fallen within the ES for both.

    However, while the velocity and pressure measurements fall with in the test ES for both many times the 1st two shots out of the clean barrel were not within the group but sometimes they were.
    Larry Gibson

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  17. #177
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    Interesting. Thanks Larry.

  18. #178
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    What if this is a paradox ???

    > We know that as the pressure increases in a ladder test of castboolit loads, the amount of obturation to the castboolit increases.
    > As that obturation increases, I suspect that friction increases.

    What if that obturated lubed cast boolit friction surpasses the friction of a unlubed J-word?

    My theory on a pressure test comparison of castboolits and j-words:
    Light loads will yield results showing J-words creating higher pressures.
    Increase the loads to the point that obturation is creating enough friction to surpass that of J-words, then results will start showing castboolits are creating higher pressures.

    One great problem of this pressure test, centers on what I have previously stated in this thread [years ago], All things can not be equal, OR BETTER PUT, all "other" things can not be equal.
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  19. #179
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    I'd like to add:
    One huge issue of "all other things not being equal" is having two projectiles that have the same shape[nose ojive] and same volume and same weight...So when they are seated in the case the same, there will be the same jump to lands (or lack of jump), and same case capacity, so there is a same burn pressure rise. Also the projectiles should be the same diameter, so the case tension is the same.
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  20. #180
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    The Lyman Cast Bullet Handbook lists the pressure of some cartridges and loads.
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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