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Check out SAAMI.org for rifle cartridge and ammunition drawings (ANSI/SAAMI Z299.4 - Centerfire Rifle - 2015). Also see page 36 for primer and pocket dimensions. There is a fascinating section on pressure measurement and procedures although geared to engineers. There is an interesting note on page 195 concerning CUP measurements vs electronic.
 

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The Shadow
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Yes, Perhaps unclenick could give you a more specific timeframe of it, but this is the gist.

Long ago there were very carefully calibrated Copper Crushers and carefully stored reference lots of powder loaded and sent to several of the majors within the SAAMI group(Federal, Remington, etc) for testing. What was discovered was that when testing over, roughly 45,000psi, Copper Crushers can report pressure "differences" on the order of 15-20,000psi. At the time this was quite well reported upon, by the magazines of the day.

I suppose it is due to the general age of loaders, and not actually reading manuals.. It stuns me still how the inter-webs is still flush with people who think they can accurately "read" pressures when they fire cases. Unknown alloy case specs, unknown primers, non-reference canister grade powder lots, and magically they assume they are more accurate than the SAAMI members...:rolleyes:

Watch your velocities, and you can be *reasonably* informed of your pressures. Regardless of specific powder charge, if you exceed book max velocities; it's because you exceeded book max pressures. You don't have a magical barrel, the extra few inches don't matter like you wish they did(that's what she said).:D

Cheers
 

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......I suppose it is due to the general age of loaders, and not actually reading manuals.. It stuns me still how the inter-webs is still flush with people who think they can accurately "read" pressures when they fire cases. Unknown alloy case specs, unknown primers, non-reference canister grade powder lots, and magically they assume they are more accurate than the SAAMI members...:rolleyes: Cheers
While there's a lot of truth in that statement, I would also say that relative pressure can be read from primers. By that, I mean that when working up a load, all else being the same, primers starting to flatten are a sign that maximum pressures for that load / chamber are being pushed.

Back in my younger, dumber days, I would push loads progressively higher in an old Springfield 1903A3 until primers flattened, then bolt handle lift would get stickier. I think I have at least 5 or 6 load combinations I pushed this hard.

I would never attempt to correlate that to absolute pressure as, even then, I knew published pressures, as well as velocities, were only applicable to that rifle/chamber/barrel length/load under those controlled conditions.

I did manage to, without destroying the rifle or hurting myself, prove to myself that the progression was predictable as long as variables were closely controlled. One thing, though, is that I never was able to correlate case head growth, as described by Ken Waters, no matter how I tried.

Lastly, I will state unconditionally that no one should ever load ammunition as described above. All published data should be used with caution and the understanding that listed maximum loads should ALWAYS be worked up to in accordance with standard, published, load development practices.
 

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The Shadow
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While there's a lot of truth in that statement, I would also say that relative pressure can be read from primers. By that, I mean that when working up a load, all else being the same, primers starting to flatten are a sign that maximum pressures for that load / chamber are being pushed.
Unfortunately that isn't true, and for precisely the reasons I stated. While generality may have a convincing trend line, that I think is a big part of why people suddenly decided they understand pressure.

Relatively speaking, you would say the left case is pushing it.







Scientifically speaking, the case on the right was from the high pressure with secondary ignitions.



The case on the left came out of one of these




The last time that I'm aware of, was in the hay-day of WWII; Olin actually published specs for 30-06 cases. They gained a reputation for having "Stonger" brass, something that is still repeated, while MANY things have changed. In any case, those cases were being built with Olin alloy C260. It had a spec'd tensile strength of Approx 75,000 psi. From what MZ5 and I have tested, recent mfgr brass(not Federal) would appear to fall in that range. So you won't notice any case growth until you approach the tensile strength. What you mean by "Maximum pressures for that load / Chamber is being pushed" is off I think. If you mean getting close to SAAMI cartridge pressure, then no; you are well beyond that. If you mean what the chamber will withstand, gotta have a rifle mfgr publish what they rate things to first, if you want to be able to compare that realistically.
 

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Darkker,

Are those charts pressure data that you developed????

Need to send you a rifle and some cartridges if that's the case.. :D

As for me, I tend to use powder/bullet combinations for which there is little/no loading information.
Example:
7mm Rem Mag
150gr. Nosler Accubond Long Range bullets
Alliant Reloder 26

Alliant does give data for a 150gr. Sierra Game King, but not the ABLR. Also, Alliant does not give start load data, just max load.

Taking the above load for a GK, I did a ladder test with 10 cartridges, with max powder at #10 round. Looking for accuracy, not absolute max load.

Do I know what my pressures are??? Heck no... Although my velocities were down some from a "standard" 150gr. load.

Back to ladder testing...

Found another "accuracy node" with a slightly higher powder charge, and a more acceptable velocity.

And try to find load data for a 7mm-08AI, that's reliable!!!!
 

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Unfortunately that isn't true, and for precisely the reasons I stated. While generality may have a convincing trend line, that I think is a big part of why people suddenly decided they understand pressure.

Relatively speaking, you would say the left case is pushing it.

I would still, respectfully, disagree. Your example does not conform to the basic constraints I outlined, that all controllable variables be equalized. Specifically, you used 2 completely different cartridge cases. Your example could easily be a result of different brass.

This isn't rocket science. While flattened primers can result from different internal ballistic events, the "trend" towards increased flattening of the primers as pressure increases, ALL OTHER VARIBLES KEPT CONSTANT, has never been disproved through the use of advanced pressure measurements, it just expands the depth of our knowledge and explains why some flattening events are not necessarily the result of gradually increasing pressure.
 

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The Shadow
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Std7mag,

Yes those are from one of our rifles. Go to: https://www.shootingsoftware.com/

And you can buy a Pressure Trace II system.
If they only list the max, then back off by 10% and start loading. Regardless of the charge weight, when you meet or exceed max velocity, you exceeded max pressure.



Dollar Bill,

I think you are missing some needed nuance, reloading actually truly can be rocket science.
Unless you can get specs for each lot of cases, and each lot of primers, each lot of powder; you can NEVER say that all things are equal. I grant you that the cases from my traces are different, the primers came out of the same 100 pack tray.
Again, the cases are different. But sticking to your line of thinking, that load with the R-P cases, isn't a dangerous load yet; which quite obviously is false. With as nasty as that secondary ignition was, the next "gradual increase of pressure" could well have been catastrophic as it was already beginning to run away. There was no odd report, recoil or ejection issues; and as you can see due to the stopping and starting of the bullet, only looking at the velocity would have you believe that the "pressure was low" which it was not.
So again better than nothing? Certainly! ANY form of accurate? Absolutely not.
Take one of my posts from this spring/last fall, about soft case heads on Federal cases. Simply by what happened you would say that load was more than the system could take. The truth is the cases are soft, and the load pressures were PT verified well under SAAMI max. Unless you can accurately quantify your inputs, you can't judge the outputs ACCURATELY.
Since no one will tell you the specs on the inputs, the outputs are only By-guess-or-by-golly.
 

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The Hog Whisperer (Administrator)
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Bill,

The worst primer flattening I have ever seen in a gun I own, was when I used small pistol magnum primers in some .38 reloads. No longer recall WHY such a thing was done... but they were ordinary .38 reloads, and fired in a .357 mag gun. So zero chance of pressures being an issue.

Granted, a very unusual situation and certainly I was not following the published data. But from the flattening you'd have thought it was an overload in a .270, or something.

Food for thought.
 

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Flattening can and does occur from causes other then over-pressure. Excessive head space is one. If it's other then pressure, it's generally because, for some reason, the case head is not firmly against the breech face when the round goes off.

All this is known but beside the simple point I was trying to make: When I am working up a load, using know good cases that I separate into consistent lots, have less then .002" difference between chamber and cartridge headspace, loading a standard medium capacity cartridge such as a 308, changing only the charge weight in .2 to .5 grain increments, with over 38 years of experience and well over 800,000 handloaded cartridges under my belt, I can tell for a fact when my loads are starting to approach maximum allowable pressures for my gun and load, based partly on primer indications.

You guys can continue to throw out examples were you did or did not experience flattened primers for whatever reason but that will not change the fact that an experienced handloader can, in fact, learn quite a bit about the load, under well controlled conditions, by looking at the primers.

That's all I'm saying.

And I really mean that: I'm done with this conversation. Thank you all for your insights and sharing your experiences. :)
 

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The Hog Whisperer (Administrator)
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Bill, no problem. Be safe and happy handloading....
 
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