.357 magnum load data
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Mr_Flintstone
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Take a look at https://www.leverguns.com/articles/paco/357_magnum_and_the_literature.htm. Pressure talk starts in paragraphs 5-7, but the whole thing is worth a read.
fxvr5
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That article claims that the old 357 pressures were in the 40,000 to 50,000 psi range (45,000 to 47,000 psi according to Elmer Keith), and that with current commercial ammo the pressure has been lowered to high 30,000 psi range.
Today SAAMI says the CUP pressure max is 45,000 CUP, and the psi max is 35,000 psi. These are measured two different ways. The CUP is measured with a copper crusher, and psi with a piezoelectric transducer.
The problem with the numbers in the linked article might be just confusing terminology. They might be confusing CUP with PSI. Here’s an example of why: the 1951 edition of the #38 Lyman Ideal handling manual has a short section on pressure, page 121.
Link to #38. https://www.nzha.co.nz/wp-content/uploads/2015/08/IdealHandbook38.pdf
It describes the copper crusher method, and includes a drawing of a copper crusher, but says the pressure is measured in pounds per square inch. But we don’t use psi for the copper crusher today. We use CUP units. I can speculate that at some point someone said they should just refer to copper crusher units as CUP and not psi anymore.
Thus, old references to psi might really mean CUP.
More information: The Lyman Ideal book #38 says with respect to the copper crusher (starting at the end of page 121), “The figures are considered as representing the pressure in thousands of pounds per square inch but in reality they are nothing of the kind. They are numerical values the usefulness of which is largely dependent upon the knowledge and experience of the men taking the pressures.”
So here, copper crusher measurements are referred to as psi. As noted, we don’t do that today.
Also, the author at the link says, 15.5 grains H110 under the 170 grain jacketed bullet gives 1662 fps at a cost of 40,800 cup (44,200 psi). I’ve no idea where the conversion from CUP to psi came from. I didn’t see the author’s method for doing that, but I might have missed it. The problem is that there is no reliable, agreed upon conversion method. And if you go by the max pressure limits listed by SAAMI, 35,000 pis = 45,000 CUP.
So, lots of confusion about pressure terminology.
The author gets much data from the Lee load manual #2. If I understand it correctly, Lee’s data is just copied from other sources.
Mr_Flintstone
Member
I agree that in the past, copper crusher data has been listed as PSI, and it is very confusing sometimes. I feel that most certainly though, Elmer Keith knew the difference between the two values, and I find it very hard to believe that Paco Kelly would confuse the two. That said, the literature isn’t always clear about whether PSI and CUP values were directly measured or somehow converted.
What I took from all these bits of information was that 46,000 CUP in 357 Magnum with slow powders like H110 and 4227 doesn’t necessarily produce the same PSI as faster powders like Bullseye. If that is the case, and I don’t know that it is, then setting a fixed PSI pressure might result in lower charges with some powders than what was originally accepted as safe when the cartridge was adopted. That may be the reason that some publishers hang onto CUP measures for some powders and cartridges; so they can publish higher charges and still fall within SAAMI safe margins. Or I could be wrong completely.
What I took from all these bits of information was that 46,000 CUP in 357 Magnum with slow powders like H110 and 4227 doesn’t necessarily produce the same PSI as faster powders like Bullseye. If that is the case, and I don’t know that it is, then setting a fixed PSI pressure might result in lower charges with some powders than what was originally accepted as safe when the cartridge was adopted. That may be the reason that some publishers hang onto CUP measures for some powders and cartridges; so they can publish higher charges and still fall within SAAMI safe margins. Or I could be wrong completely.
GeoDudeFlorida
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Crusher units measure peak pressure. Duration is undetermined. Strain gauges measure peak pressures and include approximate duration numbers. The question is, how important is duration?
Jim Watson
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Phil Sharpe had industry connections and was able to get loads pressure tested. Of course in those days it was by crusher calibrated in pounds per square inch, so don't get all het up over a term not coined until 30 years later. The other problem is that #2400 was fairly new on the revolver scene and he only shows loads with it and his own design of bullet.
With all that understood, he maxed out at
146 gr SHP (Sharpe Hollow Point) 16 gr 2400 = 1655 fps at 35,000 psi in 8 3/4" barrel.
With all that understood, he maxed out at
146 gr SHP (Sharpe Hollow Point) 16 gr 2400 = 1655 fps at 35,000 psi in 8 3/4" barrel.
fxvr5
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The factory ballistics of the 357 have not changed much since the introduction of the round. If anything they're a little faster today than in the old days, based on the May 2023 Shooting Times article.
Mr_Flintstone
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I didn’t say they had. Companies that produce factory loads have way more resources to test pressures than your average handloader. What has changed is that reloading manuals list now list both loads standardized on CUP and PSI, and sometimes those two standards don’t necessarily agree on what a max load is. SAAMI says they both are as long as they are measured in the appropriate manner, so I think that leaves it open to whoever is doing the loading to choose the one they want to use.
fxvr5
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One would expect Lyman to know the difference between CUP and PSI, too. Yet, they report copper crusher values in psi in their 1951 manual, and they are in the industry.
Mr_Flintstone
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One would think that, but they did a lot of things in the 1950s that we can look back on as not exactly 100% correct.
fxvr5
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Sorry for the long post, but, to address some questions . . .
Looking into this a little more, in the past, copper crusher CUP results used to be reported as psi.
Summed up quickly here: https://www.chuckhawks.com/pressure_measurement.htm
“Before the 1960's it was common to leave off the CUP and most publications simply labeled these readings as PSI, or pounds per square inch. If the pressure figure dates to the 1950's or earlier, it was determined by the crusher method, even if it is expressed in terms of PSI.”
Piezoelectric transducers were invented in the 1960s. The psi numbers in the 1951 Lyman Ideal Manual preceded the existence of piezoelectric transducers, but referring to CUP pressure as psi would have been the norm at the time, though not technically accurate with respect to measured pressure.
More information here: https://en.wikipedia.org/wiki/Copper_units_of_pressure
From the wikipedia page:
“A chamber pressure measured with a copper crusher gauge would there be expressed in psi (CUP) in the British Imperial system and United States Customary system, bar (CUP) in the metric system, and MPa (CUP) in the SI system.”
The length of the copper plug is measured and compared with standards of plugs that have been crushed with a known psi pressure. From this, the psi pressure is estimated.
“The length of the crushed cylinder is measured and compared to a chart of lengths resulting from crushing cylinders with given amounts of pressure, and the corresponding force is the CUP or LUP pressure value.”
“The amount of deformation is compared to the amount of crushing produced by different pressures in pounds per square inch.”
“While CUP and LUP numbers were intended to be comparable to the crushing power of a given pressure in psi (lbf/in2), the numbers are not equivalent. ”
“Until the invention of measurement transducers in the 1960s, crusher guns were the only reliable method for estimating chamber pressures. With the availability of inexpensive, reliable transducers since the 1960s for actually making chamber pressure measurements, the industry almost universally has begun to move away from crusher guns for estimating chamber pressures, towards favoring making actual measurements.” (emphasis added)
This would explain Keith’s 40,000+ psi numbers if they were made and reported before the piezoelectric transducers were invented, and might also account for Paco’s numbers, too, depending on where Paco got their information and whether they were aware of the history of the terminology.
From SAAMI’s history of transitioning from CUP to psi: https://saami.org/about-saami/history/
“The 1970s was the start of three decades of transformation and modernization of the firearms and ammunition industry. SAAMI started the transition of the decades-old copper crusher chamber pressure measurement system (CUP) to the modern piezoelectric transducer chamber pressure measurement system (PSI).”
Looking into this a little more, in the past, copper crusher CUP results used to be reported as psi.
Summed up quickly here: https://www.chuckhawks.com/pressure_measurement.htm
“Before the 1960's it was common to leave off the CUP and most publications simply labeled these readings as PSI, or pounds per square inch. If the pressure figure dates to the 1950's or earlier, it was determined by the crusher method, even if it is expressed in terms of PSI.”
Piezoelectric transducers were invented in the 1960s. The psi numbers in the 1951 Lyman Ideal Manual preceded the existence of piezoelectric transducers, but referring to CUP pressure as psi would have been the norm at the time, though not technically accurate with respect to measured pressure.
More information here: https://en.wikipedia.org/wiki/Copper_units_of_pressure
From the wikipedia page:
“A chamber pressure measured with a copper crusher gauge would there be expressed in psi (CUP) in the British Imperial system and United States Customary system, bar (CUP) in the metric system, and MPa (CUP) in the SI system.”
The length of the copper plug is measured and compared with standards of plugs that have been crushed with a known psi pressure. From this, the psi pressure is estimated.
“The length of the crushed cylinder is measured and compared to a chart of lengths resulting from crushing cylinders with given amounts of pressure, and the corresponding force is the CUP or LUP pressure value.”
“The amount of deformation is compared to the amount of crushing produced by different pressures in pounds per square inch.”
“While CUP and LUP numbers were intended to be comparable to the crushing power of a given pressure in psi (lbf/in2), the numbers are not equivalent. ”
“Until the invention of measurement transducers in the 1960s, crusher guns were the only reliable method for estimating chamber pressures. With the availability of inexpensive, reliable transducers since the 1960s for actually making chamber pressure measurements, the industry almost universally has begun to move away from crusher guns for estimating chamber pressures, towards favoring making actual measurements.” (emphasis added)
This would explain Keith’s 40,000+ psi numbers if they were made and reported before the piezoelectric transducers were invented, and might also account for Paco’s numbers, too, depending on where Paco got their information and whether they were aware of the history of the terminology.
From SAAMI’s history of transitioning from CUP to psi: https://saami.org/about-saami/history/
“The 1970s was the start of three decades of transformation and modernization of the firearms and ammunition industry. SAAMI started the transition of the decades-old copper crusher chamber pressure measurement system (CUP) to the modern piezoelectric transducer chamber pressure measurement system (PSI).”
Mr_Flintstone
Member
You might also find this article from Guns and Am interesting. https://www.gunsandammo.com/editorial/ammunition-pressure-testing/458750 It talks a lot about CUP, LUP, and transducer measurements.
fxvr5
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Yeah, I saw that.
