OK. I know this is a dumb question, but are the published pressures in reloading manuals the internal cartridge pressure, or the max barrel pressure; or are both the same thing?

There are NO dumb questions in the reloading field. The more knowledge one has the better the reload product will be and the safer the shooter will be. ........ Semantics........ The maximum pressure developed will be in the chamber and for a short distance into the barrel depending on where the bullet is at the instance the powder combustion has maxed out. From that point on the chamber/bore volume is increasing and the combustion pressure is decreasing. So, the pressure starts dropping but not significantly. Therefore the main component of muzzle blast is that pressure being released suddenly as the bullet clears the barrel. .... The preceding is based on what happens in a closed chamber/bore assembly as a rifle. The situation is slightly different in revolvers with the open gap between the chamber and the bore. ..

Each powder has its own characteristics.............

If you shoot different powders in a low light situation, you will find
out that all the powder will look like the 4th of July fire works.

There will be "Fire Balls", "Circles", "Twisters", "Shotgun" and "Sparkler" effects, coming out the end of the barrel.

All rise and fall at different rates in the power scale that cause their pressures.
One reason some are used for light target work and others for
getting the best results for long range work.

Yeah, its a dumb question... JK, JK!

I believe the published pressures are just the measured results of the powder charges listed...

Heh, it kind of looks like we may each be answering your question in a different way. This may end up being a pretty interesting discussion!

Agreed -- NOT a dumb question, never a dumb question in handloading unless someone shows up, exercises complete lazy ignorance and talks about doing really reckless and dumb things without learning basics. Your question is a compelling one, and a darn good question.

My answer is this:
Published pressures in reloading manuals are quite simple reports and results. Published load data has never been a strict recipe -- published load data is a clear example of what they did, the conditions in which they operated, the result they got, and what they believe you should reasonably expect if/when you attempt to use their outline for your own loads.

Let's dissect that a bit!
They tell you the SAAMI standardized cartridge, they tell you who made the bullet, the materials of the bullet, the design/shape and the weight of it, they tell you the powder charge manufacturer, type and weight and they tell you the average velocity returned with those items.

Often, but not always, they also include other interesting points that matter... such as, primer brand/type, barrel length, max pressure recorded, ambient temperature and sometimes even elevation, COAL of the round, actual firearm or test receiver and other assorted information.

They add all of those bits because those bits matter -- they don't print those items because you MUST specifically replicate them, they add those items because they had a part in the results.

I think a lot of handloaders see published data and feel as if it is very strict and must be copied to the Nth degree. This is not the case. Published load data is test results that we can use as a knowledge base to build our own loads with reasonable expectations.

One of the absolute cardinal rules of safe handloading is to start UNDER and "work toward" an end. We don't have to use a Remington primer when the published load data shows one, because we are starting lower and safely witnessing the results.

Hope that doesn't muddy the waters.

In reading your question a second time, I feel as if I probably didn't answer it specifically, so I'll try again.

In published data, the pressure shown is the MAXIMUM peak pressure recorded during the event.

I usually default to .44 Magnum here because it's the easiest to detail for me. If you built a 240gr JSP load in .44 Mag with a max published load of Titegroup, you would build ammo that reaches right up to the 36,000 PSI Max allowed by SAAMI for .44 Magnum, but that load would return a couple hundred feet LESS velocity for the bullet. This is because that ultra-fast burning powder peaks in pressure far too early and the bullet won't ever reach lofty FPS goals that the .44 Mag with the proper (slower burning) powder can very safely reach.

A maximum published charge of H110 under the same bullet in the same revolver, when compared to a Max of Titegroup will:
--give faster velocity
--sound much more like a true max .44 Mag round
--give more recoil energy
--actually be a SAFER and more consistent handload due to a reasonable pressure curve

So yes, the pressure listed in published load data is the peak pressure returned in the test results as they experienced them.

How about a simple answer:
internal cartridge pressure

Most bbl's/firearms are made to withstand 1 1/2+ times the max saami pressure of the internal cartridge pressure of the caliber they are chambered for.

What good is a bbl if it's only rated/made/designed to withstand the max pressure of a cartridge???

A simple question with a somewhat complex answer. Boyle it down and you could say that it's the Peak Pressure recorded within the case during the event. However Boyle's Law states that pressure in a Closed System will be distributed equally throughout the containment, so that is also the pressure the barrel is exposed due if the pressure event has a time period that has the bullet within the barrel at the time point of the peak in pressure. What this means is that the powder used MAY effect whether, or how much of the barrel, will be exposed to peak pressure. BTW, there actually isn't a powder in use that burns fast enough to limit the peak pressure to the case alone so all barrels do see part of the peak pressure event however with longer barrels a fast burning powder can "flame out" while the bullet is still in the barrel and the bullet will then just be "coasting".

The pressure in a test barrel is, of necessity, measured just after the end of the cartridge. Without regard to the exact powder used, the pressure rises and falls in a curve having the general shape shown above. This specific curve is from a 30/06, but the general shape is typical.
Note the peak pressure comes early, before the bullet has had time to accelerate, and the pressure starts to drop as the bullet moves down the barrel. The residual pressure as the bullet exits gives the familiar muzzle blast.
The PEAK or maximum pressure is what tends to explode the gun.
The TOTAL FORCE or total area under the curve while the bullet is in the barrel is what gives the bullet the MV.
Thus, the way to get greater MV safely is to flatten the curve, producing higher pressure longer without increasing the PEAK: i.e., use a slower powder and more of it.


Internal Ballistics


By the way, the brass cartridge has negligible strength to contain the pressure and all the strength comes from the steel of the chamber. Therefore a strain gauge directly over the cartridge is measuring essentially the same pressure as the port on a test barrel. The strain gauge is reacting to the minute elastic stretch of the steel.

__________________
Science plus Art

Not flaming anyone but what the heck does all these long winded answers have to do with the op's question???

The op asked " published pressures in reloading manuals"

In another thread on this website asking about 4.2gr of trailboss being the same for a 38/357.

38spl 4.2gr 13,700cup
357 4.2gr 20,400cup

Every reloading manual I've ever seen/read lists the "Internal cartridge pressure" in their reloading data. Hence the trailboss loads

38spl 2.7gr 11,400cup 4.2gr 13,700cup
357 3.2gr 16,500cup 4.2gr 20,400cup

Max barrel pressure is the point where the bbl can fail.

When you reload for a revolver the cartridge pressure puts force against the cylinder walls & has nothing to do with the bbl/pressure.

But yet when you look at reloading manuals there is no difference listed in bbl pressures for say a 44mag shot in a revolver compared to a lever action. That's because reloading manuals always list the internal cartridge pressure. It has nothing to do with:
Barrels
How long the bbl is
Time the bullet spent in the bbl
Fast/slow burning powders in a bbl
Peak bbl pressure
ETC

OK you didn't under stand the long answers, so here is the short one:


The pressure testing equipment, either test barrels or strain gauges on real guns, measures the CHAMBER PRESSURES OF THE STEEL CHAMBER, but it's OK to call that the internal cartridge pressure because THEY ARE THE SAME.


The PEAK PRESSURE comes just as the bullet starts to move and DROPS as the bullet goes down the barrel, so PEAK pressure does not change with barrel length. The PEAK PRESSURE is what is published in the loading manuals as "Pressure."


For a revolver, the PEAK Pressure comes before the bullet exits the cylinder.

__________________
Science plus Art

Thank you for the short answer, very well thought out.

I guess my answer in post #7 seven "internal cartridge pressure" is too direct for most people.

The op asked:
"Are the published pressures in reloading manuals?"

A. the internal cartridge pressure
B. the max barrel pressure
C. or are both the same thing


A. Is the correct answer
b. Max bbl pressure has nothing to do with what is published in the reloading manuals.
c. Both are not the same thing. Not hardly by your own answer "For a revolver, the PEAK Pressure comes before the bullet exits the cylinder"

The PEAK pressure as you put it is no where near the bbl!!! Therefore when the op asked about published pressures in reloading manuals being the max bbl pressure.

The answer is NO!!! It's always the internal cartridge pressure.

A cylinder is not a barrel and cylinder pressure has nothing to do with the "max bbl pressure" from a load/cartridge shot in a revolver.

And yes for those of you that don't know even though a revolver uses a cylinder (that's where the PEAK cartridge pressure takes place),there is still a max bbl pressure in the bbl of the revolver. And that MAX pressure in that revolvers bbl is no where near the PEAK pressure in the cylinders.

If the question was about where, here's an answer...

Ed

Attached Images

IMG_0513.jpg (25.6 KB, 41 views)

Way too much theory and speculation for a simple question. I always try to answer questions as if I'm talking to a basic, new reloader. Peak pressure/time/distance of bullet travel, etc. are way too involved answers for this basic question from a new reloader. In a reloading manual, SAAMI pressures are not usually listed. The pressures listed are the chamber pressures with the listed powder charges, not max nor min SAAMI. Whether in a universal receiver or a real gun, it's chamber pressure. Not max. barrel pressures (whatever that is, perhaps chamber pressure?), just normal nomenclature; chamber pressure...

SAAMI and CIP specify methods for measuring peak pressure (or more exactly an average maximum pressure of a number of firings) and specify precise methods to be used. The two do not measure precisely the same thing, as the methods used are different. But both are standards. The peak pressure occurs very quickly before the bullet moves very far.

Virtually every ammunition manufacturer in the world now uses some method incorporating piezoelectric pressure gauges. The old CUP (copper crusher) method is long obsolete and is really not a measurement of peak pressure at all.

Not a dumb question, but a very good one. All of the published numbers are reference pressures that are proportional to what is going on in the chamber and barrel. If you're as old as I am you are used to seeing CUP and LUP (copper and lead units of pressure) in psi, now supplanted by piezoelectric strain gage measurements of pressure. The CUP and LUP crusher methods were standardized attempts to nail down reference pressures that were repeatable and measureable. They could not indicate the pressure curve of the expanding powder gases like piezoelectric strain gages can. Strain gages have their own set of problems. They measure strain, not pressure, on the barrel O.D., not internal pressure, so pressure must be calculated from known parameters of cartridge and barrel materials and dimensions. The calculation could be a bit tricky as the end effects of a barrel's receiver make three dimensional stress calculation a necessity to get an accurate pressure calc. So even piezoelectric strain gage measurements of pressure are indirect, but far more accurate and repeatable than crusher methods, able to calculate a time history, or pressure curve, and closer to actual pressure in the bore.

All this blather is indirect lore and here-say on my part. Perhaps someone with ballistic lab experience could chime in and further illuminate this subject.

For those that do not want to "wade" through the SAAMI PDFs

Here is the Wiki version

also the link that OKFCO5 posted

The bottom line is that the test data in manuals show safe loads that do not exceed the establish MAX pressures, so exactly how it is determined really doesn't matter, just stay below those and live to load another day.

Small arms ammunition pressure testing - Wikipedia

Internal Ballistics

__________________
Still Running Against the Wind

For all practical purposes they are the same thing.

Actually, SAAMI and CIP proofing standards are congruent at 130% of maximum pressure, not 150%.

I am probably as old (or nearly as old) as you are, but you don't have to have six decades or more in the rear view mirror to encounter CUP and LUP. Just look at the Lyman Manual #49 which publishes pressures derived using CUP, LUP or Piezo; sometimes mixing them up in the same table where they are differentiated by "C", "L" or "P".

"...now supplanted by piezoelectric strain gage measurements of pressure...They measure strain, not pressure, on the barrel O.D., not internal pressure..."

Strain gauges work on an entirely different principle from piezeolectric gauges. Strain gauges work on changes in resistance as a result of elongation or compression, and are typically affixed to the sidewalls of barrels (or other items under study) with adhesives such as cyanoacrylates or epoxies. There are some types of solid state strain gauges used for special applications. What they measure is the elongation or shortening under a given load of whatever they are attached to. Ammunition manufacturers do not use strain gauges for pressure measurement, although there is instrumentation available which can be used to estimate the peak pressure in gun barrels by gluing a strain gauge to them. Piezoelectric pressure gauges use quartz crystals which generate an electrical output proportional to the load (pressure) on the gauge. They have an extremely rapid response and can instantly follow the pressure in the barrel from the ignition of the propellant until the bullet leaves the muzzle. Piezo gauges have been used in some form for ballistic pressure measurements since before WWII (most notably for pressure measurements in artillery pieces), but it was only in the 1960s that suitable electronics became available to make them practical and easily usable on a wide scale. Piezo gauges are almost unimaginably superior the old copper (and lead) crusher methods. There are many applications for piezo instruments in measuring forces and weights. At one time I was using arrays of piezo gauges in special fixtures for measuring air blast overpressure from the detonation of explosive ordnance.

Everyone seems to be quoting the saami method for testing pressure.
Quotes from your own link/saami method:
1. conformal Piezoelectric Quartz Transducer
2. The SAAMI pressure testing protocol uses test barrels that have a HOLE located in the chamber at a location specific to the CARTRIDGE.
3. The SAAMI conformal transducer is fitted into a hole that PENETRATES THE TEST BARREL CHAMBER in such a way that the transducer's face, precision machined to match curvature of the chamber wall at the mounting location a specific distance from the breech face, functions as part of the chamber wall.
4. When the CARTRIGE is fired the gas pressure causes the CARTRIDGE CASE to expand, contacting the chamber walls.
5. The portion of the CARTRIDGE CASE in contact with the face of the conformal transducer exerts a pressure on the transducer which in turn generates a minute electronic impulse that is amplified and results in a reading in pounds per square inch (psi).
6. The SAAMI conformal transducer has the benefit of not requiring a drilled CARTRIDGE CASE and the corresponding challenges of inserting and alignment required of drilled CARTRIDGE CASE. Instead it requires a simple pressure test of a sample CASE from the lot of CARTRIDGE CASES being used in the test ammunition. This pressure test determines the gas pressure required to cause the CASE to expand and come in contact with the face of the conformal transducer upon firing.
7. This measurement is referred to as the "offset" and makes allowance for the "loss" of that gas pressure prior to the CARTRIDGE CASE coming in contact with the transducer and generating the impulse.

In layman's terms, the saami drills a hole in a test bbl and puts a transducer in the hole that comes in contact with the CARTRIDGE CASES to measure the INTERNAL PRESSURE being exerted on the CARTRIDGE CASES of the loads being tested.

Nowhere does it state or imply in any way the saami is using transducers on the test bbl themselves.

The saami are measuring the internal pressure of the load by putting their measuring equipment on the CARTRIDGE CASES. The saami also takes into account the "offset"/amount of pressure it takes to expand the CARTRIDGE CASES so that the CARTRIDGE CASES can come into contact with their transducers/measuring equipment.

The saami adds the offset pressure of the CARTRIDGE CASES to the internal pressure of the loads measured from the CARTRIDGE CASES against the transducer to get the internal pressure of the load they are testing.

When you see the #'s/pressures written down in the reloading manuals it got there from measuring the pressures exerted on the CARTRIDGE CASES + adding the offset pressure of the loads/CARTRIGE CASES being tested.

As far as the CUP gauges/testing goes. My father in law worked at the old s&w ammunition plant 15 miles away for 20+ years/until the day it closed. Saw a little bit of testing over the years. One of the most interesting testing equipment I've seen was at the Ohio gun collectors show several years ago. A guy had all the test bbl's/extra cups that were used by winchester to test their 410/20ga/16ga/12ga/10ga shotgun shells. For some odd reason all those different test bbl's had holes in them and different things were put in them to make contact with the CARTRIDGE CASES to measure the internal pressure of those CARTRIDGE CASES.

Anyway don't take my word for it, read the link posted above (not my link). You will see that the saami tests the internal pressures of the CARTRIDGE CASES.

Hodgdonreloading.com does this too for cup and psi. I contacted them no too long ago as to why some of their pressure measurements for .38 special using certain powders used CUP, and other powders used PSI, and they sent me an interesting reply. They said that they had a lot of older copper crusher test barrels that they still used, and as they wore out they would be replacing them with PSI measuring barrels.

It didn't really answer my question as to why 38 special 125 gr LRNFP loaded with Titegroup was measured in cup, but the same cartridge loaded with Trail Boss was measured in PSI. Maybe they have multiple barrels for each caliber, and just chose a different one for each.

They fed you a line of SH**.
They use their "old" data from testing powder when it 1st came out and just keep re-printing it in their newer manuals. When they get a new/new to them powder the testing is done with modern testing equipment.

You see the same thing with all their powders. While most of the imr powders are not new by any means hodgdon tested some of them in new loads and those loads are listed in psi. That's why you see new bullets or calibers listed in psi like the WSM. But the 308 winchester has a mix of cup/psi, hence old powder, new/new to them powder.

A link to older hodgdon manuals. If you look at the 2002 manual you will see the same loads/cup pressure still being used to this day.
Hodgdon Manuals

You will also see that they were using old "cup" data back in 2002 along with the new "psi" data. (357sig)
I have an old hodgdon manual #25 printed in 1986 and a lot of those loads in that 1986 book are the same cup loads still used on the hodgdon website to this day.

An instance where one asks the time & people always have to tell you how to build a clock. Chamber pressure, nothing to do with pressure as the bullet moves down the bbl. Well unless there is a restriction in the bbl.

__________________
NRA Cert. Inst. IDPA CSO

Ain't that the truth!

A Grandfather Clock no less.

__________________
Still Running Against the Wind

The copper crusher method (CUP) and the transducer method (PSI) are taken at the approximate mid point of the cartridge case.

Strain gauges are used for measuring chamber pressure when the above two methods are not used and are glued to the outside of the barrel.

Example from the Lyman manual,using a .223 both a universal receiver and a AR15 were used for pressure testing. The AR15 pressure data was from a strain gauge. And the universal receiver gave both CUP and transducer PSI readings.

Bottom line, most reloading manuals will tell you how the chamber pressure was measured.


Cartridge Pressure Standards

NOTE, pay attention to the link above and the older British base crusher system using oiled proof cartridges. And why oil or case lube on the case or in the chamber will greatly increase bolt thrust.

Below from the 1929 British Textbook of Small Arms. (base crusher system)

Note that the NATO standard (STANAG) pressure measurement method uses a piezo gauge located at the case mouth. It is typical that the NATO method usually results in slightly lower peak pressure values vs. the SAAMI conformal piezo measurement method for the same round. No real problem with that as all NATO pressure specifications are internally consistent. Just remember that if you see pressure specifications for military ammunition, it is not the same as SAAMI, just as CIP is not the same as SAAMI.

"An instance where one asks the time & people always have to tell you how to build a clock. Chamber pressure, nothing to do with pressure as the bullet moves down the bbl. Well unless there is a restriction in the bbl. "

Ballistic pressure measurement is a very complex topic, and it's not really possible to discuss it without building a few clocks.