What is the rule ...."is" there a rule ?

M

Metal god

New member
Hey guys and gals and ......

Ok I know there is no rule but I remember reading here about max pressures in manuals can say a lot ... something........nothing :eek::D

It went something like this , in general the higher the max pressure is for a given specific cartridge/load the more consistent the burn of that specific powder primer etc combo is . ( Talking PSI not CUP or trying to compare them ) Meaning - lets say the Max Allowable Pressure for cartridge A is 30,000psi . The powder that is the closest to that cartridges MAP in the manual is the most consistent and or stable at those max pressures for that cartridge ?

You see it all the time in manuals that powder A max pressure is 29,400psi while powder B max load/pressure is 28,600psi . Why don't all powders have there max load at the MAP of 30,000psi for this example .

I remember there was a general rule about this or an un spoken rule because I know there is no actual rule on this . I got to thinking about this when I started looking up +P loads and found the data and maybe more specific the powder/s available for +P loads seem to be much less then the standard loads . This got me thinking ... because you/they are pushing the pressure limits . You should only be using the most stable and or most forgiving powders in these hotter loads ???

Another reason is that I have many pistol powders from fast to very slow burning and when I look up +p loads I almost never have the powder/s needed for those loads regardless of cartridge .

Anyways I'll leave it there for now , I'm sure this topic will get a few opinions . ;)

Thanks MG
 
I'm probably going to sound like a lone voice in the wilderness the way I look at these things, feel free to disagree and correct me if I'm actually wrong.

Consider some things about the questions you are asking and what is involved, and how some of the things involved are SAAMI (Industry standards), industry "best practices" and variables in loads.

MAP can be Max Allowable Pressure, but it can also stand for Mean Average Pressure. Its important to know which it is, and context will usually tell you.

So, what is "Max Allowable Pressure"?? (not the number but the concept)
It is an industry standard, a limit on the WORKING PRESSURE of ammunition. It is a level chosen to be safe in all firearms made for that round. It is NOT proof pressure, it is not the pressure that blows up your gun, its the max limit set for use in every gun all day, every day, day in and day out.

You chose an example with a limit of 30K psi, so I'll use that in my examples as well.

The powder that is the closest to that cartridges MAP in the manual is the most consistent and or stable at those max pressures for that cartridge ?
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I'd say possibly, but I also think when you're looking at the "closest to" your pressure limit vs one slightly further away that you're looking at a small degree of difference in "efficiency" and one where the difference may be calculated, but may not be something the shooter can determine from shooting.

You see it all the time in manuals that powder A max pressure is 29,400psi while powder B max load/pressure is 28,600psi . Why don't all powders have there max load at the MAP of 30,000psi for this example .
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The answer is actuall fairly simple but not really obvious to everyone. The reason the data ends at 29,4 for powder A and 28,6 for powder B is because that's where they chose to stop.

Which begs the question, "WHY did they stop there?" and often the answer to that is load variation. The object (I believe) is to get close to, but not exceed the established limit. SO, lets say the load is 10gr of Powder A and generates an average of 29,400psi, but 10.1 gr generates an AVERAGE of 30, 200psi. That's over the limit so they don't list that and "stop" at 29,400psi in their data.

Say its 11gr of Powder B giving 28,600psi and 11.1gr generates an AVERAGE of of 29, 800psi but some of the loads tested go over the 30K limit. Again, because SOME of the batch of loads does exceed the limit, they stop at the level where none of them do, even if its lower than the pressure Powder A turns out.

We're not talking about pressure differences that are actually dangerous, just pressures that exceed the set limit.

I got to thinking about this when I started looking up +P loads and found the data and maybe more specific the powder/s available for +P loads seem to be much less then the standard loads . This got me thinking ... because you/they are pushing the pressure limits . You should only be using the most stable and or most forgiving powders in these hotter loads ???
Click to expand...

A couple of points about this, first keep in mind that the powders listed in the various data sources are the powders they tested. Not all powders are tested. Some powders don't get tested simply beacuse they aren't suitable, meaning they won't deliver the desired velocity results within the given pressure limits. And sometimes some powders don't get tested simply becuase the testers didn't have any of that powder when they were testing. (yes, it can be that simple)

Next point is SAAMI approved +p limits only apply to a very few cartridges, the ones SAAMI has set +p limits for. For instance there is a SAAMI limit for +p 9mm, .38 Special, and .45ACP. There is no SAAMI +p limit for .357 Magnum, .44 Magnum, .45 Colt or many other cartridges.

And, if you look at the pressure data for the +p loads, you'll find they also stop somewhere short of the listed limit. Again the reason is not to exceed the given limit. IF you +p load exceeds the SAAMI limit by even a couple psi, SAAMI won't let you call it +p, because it technically exceeds the limit. So its NOT "+p" it is "+p+" for which there is no SAAMI limit. Your ammo could be 1psi over the limit or 10,000psi over the limit (and unsafe!) and its all "+p+" ...technically.

Industry standards are good things, they are set to ensure everyone is SAFE. Staying within industry standards means you will be safe. What you or I choose to do, if we choose to operate outside those standards is entirely on our heads, and, rightly so.
 
I've posted about this in the past. If you read through the information in the SAAMI standards, there are actually a number of named pressures of interest:

SERVICE
Maximum Average Pressure (MAP) where "Pressure" refers to peak value
Maximum Probable Lot Mean (MPLM) of peak pressure
Maximum Probable Sample Mean (MPSM) of peak pressure
Maximum Extreme Variation (MEV) of peak pressure

PROOF
Minimum Average of peak pressure
Maximum Average of peak pressure
Maximum E.V. (extreme variation) of peak pressure

CALIBRATION
Average peak pressure of reference load used to calibrate pressure gun results

The service MAP is the most common pressure referenced outside the manufacturing environment. The SAAMI system only uses a 10-round sample to test a load. This has limited statistical confidence, so they know a second 10-round sample is unlikely to match the first one. To cover that, they have a maximum average that any subsequent 10-round sample of the same fresh lot of ammunition cannot exceed, and that is the MPLM. They also recognize there is a tendency for pressure to increase as a lot ages because copper bullets tend to cold-bond to brass case mouths to some extent over time, raising the start pressure, so that samples taken from the same lot when it is no longer fresh can be expected to be higher, so they have another average peak pressure limit for a 10-round sample of the aging lot, and that is the MPSM. Finally, for all ammunition, the extreme spread of pressures in the 10-round sample also has a limit called the MEV. If this limit is exceeded when the ammo is fresh, there is a manufacturing consistency problem. In aging ammunition lots, pressure extreme spread that exceeds the MEV indicates something has gone wrong with the lot (powder breaking down, for example), and that it should be recalled and pulled from distribution.

So, what is the actual absolute allowable peak pressure? When the ammo is new, it would be the MPLM plus the worst-case high side of the MEV. The latter occurs when 9 of the ten rounds are below the MPLM by exactly 1/10 of the MEV, and one round is above the MPLM by exactly 9/10 of the MEV. This combination produces the worst-case high pressure, and it is just over 118% of the MAP value that we commonly refer to. The CIP standard uses a flat 115% of MAP as a hard upper limit for spread, so it is similar.

That number may seem high, but keep in mind it is still below minimum proof pressure in both the SAAMI and CIP systems.

So, why don't load manuals load all the way up to the MAP? To understand that, you first need to understand the SAAMI system is designed for manufacturers, not handloaders, and the pressures given in the system assume you have a SAAMI-standard pressure and velocity (P&V) barrel in a universal receiver to develop your loads with. The SAAMI member ammunition manufacturers who determine the standard values develop loads using one of these P&V barrels with the crusher or transducer readings calibrated by firing reference ammo in it and then scaling their readings to match the reference ammo's rated average peak pressure. So the manufacturer can do two things the handloader normally cannot do. One is that he is determining his charge weight using the actual pressure produced by the exact component lots he will manufacture a run of ammo with. This allows him to ignore variations in those lots, including the actual burn rate of his powder lot, because the pressure readings take all that into account. The second is the manufacturer measures the MEV he gets with his specific component lot combinations and is warned if there are behavior issues with how appropriate a particular lot of powder is for the load.

The handloader working from a book of recipes doesn't have any of the above nailed down, so the published load data has to be conservative to allow for that. Also, manuals provide information on a number of different powders because a handloader may have any of a number of different powders on hand that he wants to be able to use, even when they are not all the most suitable choices. As a result, some of these choices may exceed the MEV if they are loaded all the way up to MAP. To avoid that issue, the data stays below the SAAMI MAP by an amount that reflects the sort of variation in pressure they see while developing or final testing the load in pressure guns (both are done, depending on the source). Variations in powder burn rates and the differences between the handloader's gun and the SAAMI P&V gun are allowed for by working the load up from the bottom of the load range the load manual provides.
 
The staff doing the testing may have several criteria for establishing an upper limit.
They aren't going to take the time to write up a justification for each load max.

SOME PEOPLE will take up each "justification" as something to be argued or worked around.

Its easy to overthink and try to apply some general conclusion we might jump to when it is specific to one powder or load.

Some powders have relatively linear pressure curves. Some have sudden pressure spikes. Which needs more safety margin? Look at Hodgdon's website at min/max for 44 Mag H-110. Look at how much pressure 0.2 gr can get you.
A problem overthinking can get you is making up a "rule" (jumped to conclusion) from limited or irrelevant data.


We know seating depth can be critical to pressure in handgun cartridges.

Can we apply the same "rule" to 45 ACP that we apply to 45 Colt? There is a huge difference in case capacity.

Blue Dot might be a top performing +P powder in some cases. Yet Blue Dot over the years has shown some inconsistency. Lot to lot variation. Is your canister of Blue Dot 2 years old or 12 years old? Where do you draw the Max line? Do you buy 1 lb jars or 8 lb jugs?

Ball,flake,or extruded? Graphite retardant or Calcium Carbonate? Single or double base? What percentage of Nitroglycerine?
In some cases, max load is about compressed load,

A little knowledge is a dangerous thing. This "Rule" you are looking for is about like looking for relationship rules based on hair color. Lady Clairol might lead you astray.

If you want freedom to create,explore, challenge the limits, I suggest cooking over handloading. Playing with Ghost peppers vs Paprika is safer.
 
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If adding another 0.1 grains of powder puts you over the MAP limit, you stop. Thus the listed load could well be the max load that does not exceed the MAP.

Many of Western Powders loads get you right next to the MAP (I'm looking at handgun data). Some are right at MAP, and rarely one shows a pressure that exceeds MAP.
 
HiBC said:
The staff doing the testing may have several criteria for establishing an upper limit.
They aren't going to take the time to write up a justification for each load max.
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Is that what the staff who do the testing told you?
 
I think basically the strategy of using the MAP as a hard limit for most rounds instead of as an average as the manufacturers do is the method of keeping loads conservative. I have also spotted a few over the SAAMI MAP before, but it's pretty rare in normal load data, so I have put it down to mistakes. An exception is the data Western had for 223 loaded to the CIP peak pressure number of 4300 bar (62,366 psi) that Hodgdon has dropped from published data since buying them out. Prior to that, I confirmed with one of the Western techs that they had measured this using a conformal transducer and intact case and not by using the Kistler transducer with a drilled case that the CIP measures standard is based on. You can look in declassified military load data and see that for NATO-compatible ammo, which uses the same limit the CIP does, the conformal transducer is measuring around 58,100 psi when the Kistler transducers show 62,366 psi. I leaving another configuration difference out for simplicity, but the point is this was a recipe for getting pressures about 7% higher than the CIP intended.

There are other examples. Hornady, you can see in some of their plant photos, has gone to putting strain gauges on test guns. They, Sierra, Speer, and Nosler, all used to work their loads up in commercial production guns, then either borrow test barrels (Hornady) or outsource testing of their maximum loads to Alliant or someone else who did that work on contract. Comparing Hornady loads done this way to Hodgdon loads developed in pressure guns, you would get a fairly consistent 1% to 9% lower value, so you could guess they had a load test high, then just dropped to their next increment and tested that. Nosler, you can see lists of pressure for loads below the maximum that are simply calculated estimates rather than measured. Only their top loads are measured.

So there are other sources of variation and error by methodology in all this, but using the MAP as hard limit rather than an average buys them some safety margin.
 
Is that what the staff who do the testing told you?
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What is your point? Why do you ask? Are you just being antagonistic?

Over the last 55 years I've bought and read a lot of load manuals. I don't recall any that went into detail about why the called max at a given pressure level

Feel free to make honest contributions ,even if we disagree but if you just want to belittle,..... rest assured my heartfelt commentary would be most uncomplimentary. I'd elaborate but the Moderators would intervene.
 
HiBC said:
What is your point? Why do you ask? Are you just being antagonistic?

Over the last 55 years I've bought and read a lot of load manuals. I don't recall any that went into detail about why the called max at a given pressure level

Feel free to make honest contributions ,even if we disagree but if you just want to belittle,..... rest assured my heartfelt commentary would be most uncomplimentary. I'd elaborate but the Moderators would intervene.
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The source of the information matters. If the techs specifically told you that, that's good to know. If you made it up out of thin air, readers might want to know that, too.

Believe it or not, some responses on forums are made up. Some people say things that sound like known facts, when they aren't. They never bothered to check the facts before they posted. Hard to believe that people would do that, but it happens.

There's nothing wrong with checking the source of the information and its validity. In fact, I think fact checking is a good thing. You're free to disagree.

Guy Neill, who worked in the industry, has said that he worked up loads right up to the SAAMI max pressure limit. The safety margin is in the SAAMI max pressure limits. That's why there are established limits. So gun makers and ammo makers can make safe products.

See his comments at these links:

https://forums.brianenos.com/topic/41041-44-magnum-they-cant-all-be-right/

https://forums.brianenos.com/topic/302740-book-max-seems-low-for-n320-plated-124gn-9mm/

Is that a sufficient contribution to this thread?
 
Yeah, but the devil is in the details or, in this case, the phrasing. Instead of just asking, "do you have a source for that?" you said, "is that what the staff who do the testing told you?" which makes it sound sarcastic and dismissive. I ignore that sort of thing, but many will take it as trolling. So, let's just stick to a direct request for the reference.

One thing you get out of reading descriptions in manuals is that while the ammunition manufacturing system has SAAMI to set the standards of practice, the reloading materials companies don't all work alike. The upcoming NRA Annual Meeting is a good place to meet and speak with these folks, as I have done in the past. Sometimes you can clear something up (had a couple of great conversations with Dr. Ken Oehler on pressure testing at these conventions), and sometimes you get stonewalled (just ask Alliant personnel about why they warn people off Blue Dot now for 125-grain 357 loads and all 41 Rem Mag loads, and you will be met with a wall of silence). Just the way it is.

Guy Neill's comment is interesting. He says:

I don't know how other manufacturers do it, but at Speer and Hornady, the CYA factor was whatever was built into the SAAMI specs. Both have loading manuals with max loads as close to SAAMI max without going over as the tests showed. Thus, there was no added CYA factor for those manuals.
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The interesting part of the statement is "max loads as close to SAAMI max, without going over as the tests showed." The way I read that is they are using the SAAMI MAP as a not-to-exceed number rather than as the average. If so, that would be a CYA factor by itself, as that is not what SAAMI specifies the MAP to be. But it does comport with the load numbers you see from them for the most part.

The second link seems to be broken.
 
Unclenick said:
Yeah, but the devil is in the details or, in this case, the phrasing. Instead of just asking, "do you have a source for that?" you said, "is that what the staff who do the testing told you?" which makes it sound sarcastic and dismissive. I ignore that sort of thing, but many will take it as trolling. So, let's just stick to a direct request for the reference.
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But the original post sounds made up. And the people to ask, based on how it was phrased, would be the techs who do the testing. My question followed that train of thought.


Unclenick said:
Guy Neill's comment is interesting. He says:

The interesting part of the statement is "max loads as close to SAAMI max, without going over as the tests showed." The way I read that is they are using the SAAMI MAP as a not-to-exceed number rather than as the average. If so, that would be a CYA factor by itself, as that is not what SAAMI specifies it to be. But it does comport with the load numbers you see from them for the most part.
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You could ask Guy via a message at that website.
 
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Ok if I’m reading all this correctly. There is NO correlation to powder data that allows higher pressures with it a cartridge spec to being any more stable or consistent at those higher pressures?
 
Maybe I'm reading this thread wrong, but seems to me a couple of things are missing.

First: Why try to push the pressure limits whatever the are? Why try for +P+ .38 Special when you can just go to a .357 and be safe?

Second: Smokeless powder burn rate is not linear. Why do so many people assume it is? The higher the pressure the faster the burn and the higher the pressure (faster) rises.

I've reloading for over 50 years and have yet to blow up a firearm. Just keep your loads within the conservative capabilities of the gun/pistol/revolver you are using and if you need more power, go to a bigger gun. For example, my 45-70 rifle is a better choice for buffalo than my .45 Colt revolver trying to match the 45-70 ballistics.
 
Mkl yes you are reading this all wrong . Although Ive not been reloading as long as you , I have been doing it for quite some time and believe I have a good understanding. I was trying to take it to the next level of understanding is all .

As for +p loads . I have a 38spl Ruger LCR rated for +p and I’d like to get the most out of it when loading premium bullets . FWIW I don’t want to go as high as +P+ with any loads . I had just remembered UN mentioning something about this once and didn’t remember the specifics. I do remember after reading what ever was said I had chose powders that manuals had higher pressures at there max charges thinking they were a more consistent powder to use “if” I were to want max velocities. Like load for long range rifle loads .
 
Unclenick said:
I've posted about this in the past. If you read through the information in the SAAMI standards, there are actually a number of named pressures of interest:

SERVICE
Maximum Average Pressure (MAP) where "Pressure" refers to peak value
Maximum Probable Lot Mean (MPLM) of peak pressure
Maximum Probable Sample Mean (MPSM) of peak pressure
Maximum Extreme Variation (MEV) of peak pressure

PROOF
Minimum Average of peak pressure
Maximum Average of peak pressure
Maximum E.V. (extreme variation) of peak pressure

CALIBRATION
Average peak pressure of reference load used to calibrate pressure gun results

The service MAP is the most common pressure referenced outside the manufacturing environment. The SAAMI system only uses a 10-round sample to test a load. This has limited statistical confidence, so they know a second 10-round sample is unlikely to match the first one. To cover that, they have a maximum average that any subsequent 10-round sample of the same fresh lot of ammunition cannot exceed, and that is the MPLM. They also recognize there is a tendency for pressure to increase as a lot ages because copper bullets tend to cold-bond to brass case mouths to some extent over time, raising the start pressure, so that samples taken from the same lot when it is no longer fresh can be expected to be higher, so they have another average peak pressure limit for a 10-round sample of the aging lot, and that is the MPSM. Finally, for all ammunition, the extreme spread of pressures in the 10-round sample also has a limit called the MEV. If this limit is exceeded when the ammo is fresh, there is a manufacturing consistency problem. In aging ammunition lots, pressure extreme spread that exceeds the MEV indicates something has gone wrong with the lot (powder breaking down, for example), and that it should be recalled and pulled from distribution.

So, what is the actual absolute allowable peak pressure? When the ammo is new, it would be the MPLM plus the worst-case high side of the MEV. The latter occurs when 9 of the ten rounds are below the MPLM by exactly 1/10 of the MEV, and one round is above the MPLM by exactly 9/10 of the MEV. This combination produces the worst-case high pressure, and it is just over 118% of the MAP value that we commonly refer to. The CIP standard uses a flat 115% of MAP as a hard upper limit for spread, so it is similar.

That number may seem high, but keep in mind it is still below minimum proof pressure in both the SAAMI and CIP systems.

So, why don't load manuals load all the way up to the MAP? To understand that, you first need to understand the SAAMI system is designed for manufacturers, not handloaders, and the pressures given in the system assume you have a SAAMI-standard pressure and velocity (P&V) barrel in a universal receiver to develop your loads with. The SAAMI member ammunition manufacturers who determine the standard values develop loads using one of these P&V barrels with the crusher or transducer readings calibrated by firing reference ammo in it and then scaling their readings to match the reference ammo's rated average peak pressure. So the manufacturer can do two things the handloader normally cannot do. One is that he is determining his charge weight using the actual pressure produced by the exact component lots he will manufacture a run of ammo with. This allows him to ignore variations in those lots, including the actual burn rate of his powder lot, because the pressure readings take all that into account. The second is the manufacturer measures the MEV he gets with his specific component lot combinations and is warned if there are behavior issues with how appropriate a particular lot of powder is for the load.

The handloader working from a book of recipes doesn't have any of the above nailed down, so the published load data has to be conservative to allow for that. Also, manuals provide information on a number of different powders because a handloader may have any of a number of different powders on hand that he wants to be able to use, even when they are not all the most suitable choices. As a result, some of these choices may exceed the MEV if they are loaded all the way up to MAP. To avoid that issue, the data stays below the SAAMI MAP by an amount that reflects the sort of variation in pressure they see while developing or final testing the load in pressure guns (both are done, depending on the source). Variations in powder burn rates and the differences between the handloader's gun and the SAAMI P&V gun are allowed for by working the load up from the bottom of the load range the load manual provides.
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Lee loading manuals are notorious for this..

.
 
Why do these technical posts always turn into weiner measuring contests of insults? Manuals together with personal experience in the particular rifle(s) determine the limit for a cartridge combination. I have always relied on the chronograph and case measurements to determine maximum loads more than manuals.
 
Mkl yes you are reading this all wrong . Although Ive not been reloading as long as you , I have been doing it for quite some time and believe I have a good understanding. I was trying to take it to the next level of understanding is all .

As for +p loads . I have a 38spl Ruger LCR rated for +p and I’d like to get the most out of it when loading premium bullets . FWIW I don’t want to go as high as +P+ with any loads . I had just remembered UN mentioning something about this once and didn’t remember the specifics. I do remember after reading what ever was said I had chose powders that manuals had higher pressures at there max charges thinking they were a more consistent powder to use “if” I were to want max velocities. Like load for long range rifle loads .
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Okay, sorry for the misunderstanding. I have some experience with mega-loads since I have all the way up to a Bowen hand cannon that started life as a .44 mag and now is a 5-shot 50,000 psi .45 Colt built on the Ruger Red Hawk frame. Not fun to shoot now that 70 is several years behind me, but would be a good test frame for any .45 Colts I wanted to play with! Think I will leave that testing to you younger guys.:D:D
 
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