The truth about "pressure signs"

[counterclockwise]

Which brings us to measuring case heads. This method was actually used by the reloading manual publishers for many years. It depends upon an experienced user with a blade micrometer, taking precise and repeatable measurements at the correct area of the case, and using the same lot of cases.

This is probably the most accurate method of checking for overpressure for most reloaders. It is still referenced in the ABC's for Reloading in the later editions. The hardness of the case head is probably not going to change over refurbishing/reloading cycles because it is already very hard and (under normal circumstances) unyielding. Bottlenecked case chambers typically pose the web of the casing (rear end of the case containing the charge pressure during firing) at the opening of the chamber. Chamber pressures that expand the case web radially beyond yield stress level should be taken seriously.

For the .308 case family of configurations ( .243, .260Rem, 7mm-08, .308Win, .358Win and .375Jag) there is an FEA analysis using LS-DYNA code at this website. It is worth going there and looking at the results. At the bottom of the report, the translation of residual expansion (post yield strain) after firing back to maximum chamber pressure is presented.
http://www.varmintal.com/a243z.htm

IMO, the problem with the primer flattening flag (primer cup assumes the shape of a .22 rimfire case) is that commercial rounds can end up looking like that. I have some fired rounds of .308 winchester hunting ammo that have severely flattened primers. Same goes for case head appearance. Take a look at some fired RSAUM cases sometime. I have photos where the RSAUM Remington ammo case head begins to extrude up the ejector pin hole. This causes some confusion in the judgement of the visual inspector.

That is a good set of photos presented up top. But, the lower right photo is not a overpressure sign. That is the end game we should all strive to avoid. I think the term "case head separation" does not do it justice. That should be "case head failure" or "case head structural failure". Damage of the firearm and threat to the user is assured in that situation. Superheated plasma at 50,000+ psi pours out the back, often times vaporizing the primer cup and anvil, dumping onto the bolt face, melting the firing pin tip, curling up the extractor claw, going on back and down inside the bolt splitting it like a log splitter, pressurizing the annular space around the bolt, and splitting the bolt carrier (in the case of an AR, pressurizing the aluminum structure of the upper receiver splitting it open, blowing down through the magazine bulging and blowing out the floor plate).

 

[ranger335v]

I won't argue, neither of us will change the others mind. But, I will address ONE point you mention:

"This strikes me as fairly circular: "Pressure signs are valid in individual rifles because if the individual rifles don't show any pressure signs they are safe, so pressure signs are valid."

Exactly. A given pressure in a given rifle with a given set of components assembled in a specific way is or is not safe in how well it can handle that specific pressure. It's being below or above SAAMI max specifications becomes irrelivant. A cheaply made gun can easily be hazardous with "normal" ammo. A high grade gun may easily handle pressures well above SAAMI specs, that's why the old reloading data you mention as being down graded was, in fact, safe before. That the old data was indeed safe is confirmed by the fact that it was safely used by thousands of shooters for many years.

Bottom line, it seems you and we basically differ on what constitutes a "safe" load. You have obviously agonised over all this, a lot, but I believe you have not yet arrived at the best perspective. It seems you strongly feel that anything at or below SAAMI levels is safe and anything higher is, automatically and by that single fact, unsafe. I don't, it's a lot more complex and variable than that. Common knowledge and vast "real world" experiece bears me out, not just my own experience but that of MANY others.

In fact, your own observation that soft/thin cases do tend to show signs of pressure while others do not is an assent to my position! That's what I meant when I said your statements are contridictory, and they ARE!

Again, we are loading for and shooting guns, not SAAMIs! What's safe is safe, regardless of the psi numbers produced.

 

[Vern Humphrey]

A given pressure in a given rifle with a given set of components assembled in a specific way is or is not safe in how well it can handle that specific pressure. It's being below or above SAAMI max specifications becomes irrelivant.

Correct. Setting aside those of us who shoot wildcats for which there is no pressure-tested data, the proper use of "pressure signs" is to start at the recommended starting load in the book, and work up slowly. If pressure signs appear, stop. Backoff and stick with the next lower load.

If pressure signs do not appear, go with the max published loads if you wish.

 

[Wildfire]

Primers

Hey there:
I ma not going to get into this to deep , but the one part I did notice and did not see covered. Was , The standard firing pin reach ...
A pierced primer may or may not be a PSI sign..
.055" is standard firing pin reach on most rifles. If it is too long you will get pierced primers with even a good load...

Just figured I would toss that in there ....
Keep it up you are all doing well with this............

 

[.38 Special]

Ranger, you are admitting that your reasoning is circular. It's a closed loop of "A load that shows no pressure signs is safe because it shows no pressure sign because it's safe because it shows no pressure signs..." Meanwhile, there is absolute proof that a load can demonstrate no pressure signs while exceeding SAAMI specs by a wide margin. I suppose the argument might be that SAAMI specs aren't terribly important, but that's not an argument that I find very persuasive.

I will grant, however, that many people have worked up many loads using pressure signs and have gotten away with it. This is not because pressure signs are valid measurements of pressure (or safety), it is because modern rifles have a large safety margin and can usually put up with a great deal of foolishness. The troubles arise from folks who keep adding powder until they get pressure signs, then back off just a hair until said signs disappear. They think they are "safe", and may indeed be, but the only thing we actually know is that the load probably exceeds specification by some amount, and so the shooter is now using up some of his rifle's margin of safety -- by how much is, again, unknown. If it's significant, then he may be much closer to catastrophe than he might think.

I know we all think we are immune to a small powder measuring error, or a case neck left a little too long, or a 190 grain bullet in a 180 box, or even just a day 20 degrees warmer than the day we worked up the load, but the archives are full of pictures of defunct rifles owned by people who thought the same thing. Leaving our safety margins intact can prevent such things. Pushing them makes no sense, considering -- yet again -- that if you need a bigger cartridge you can almost always address the need by buying a bigger cartridge.

 

[Wildfire]

.38 Speacial

Hey :
That was MASTERFULLY Said............

 

[fguffey]

then there is the ideal the bullet, case, powder and primer can accelerate to the speed of the firing pin preventing the firing pin from crushing the primer (in .055 thousands of travel)?

And the firing pin spring has verified the loads as they were tested, a punched (pierced) primer is the results of the firing pin unseating, meaning the pressure inside the primer is greater than the ability of the spring to contain it. Yes a pierced primer is a sign of high pressures when it happens developing heavy loads, remedy? get a stronger spring? this could get the rifle past one warning then it would be on to the next warning.

Then, a shallow primer dent, did pressure inside the primer hammer out the dent, was the case too short from the head of the case to the shoulder or was the shallow (or no dent) caused by a short firing pin, even though the round fired?

F. Guffey

 

[ranger335v]

" Meanwhile, there is absolute proof that a load can demonstrate no pressure signs while exceeding SAAMI specs by a wide margin."

You haven't said it but, I will ask again, does it follow that SAMMI ammuniton specs are, by themselves, the guide to what is "safe", regardless of how well the weapon and case are performing? Disregarding completly how well or poorly designed and made the weapon it fired in is? Meaning safety in a load is dependant on an abstract pressure number, standing in isolation?

That's simply NOT so! The SAAMI specifications are no more than an AVERAGE pressure limits and a reasonable guide. But, it's NOT an absolute point that can't be crossed without the hazard of death and is quite safe if we stay under it. Again, history's experience and our loading manuals confirm that.

Check the loading tables for a 45-70. Note that most manuals have at least two, some have three ranges of loads for different rifles. And they ain't SAAMI, they are rational adjustments made to SAAMI tables in order to utilize the greater strength of newer cases and rifles and STILL be SAFE!

I'm circular? Sorry guy, but YOU are circular; "The rule is the rule, because it's the rule!"

Well, yeah... but not always. With all due respect, I have lots of hard evidence and common sense while you have the "rule" and no more.


"I'm already in hot water over on the milsurp thread, so I might as well keep digging!"

Guess so. Is that a California thing?

 

[Grump]

The summary:

1. Loading UP to "pressure signs" is almost guaranteed to yield a load which exceeds SAAMI or CIP or other specifications.

2. A notable exception to this statement is the flattening of primers. Head clearance between the cartridge case in its forward-most position, and the boltface/breechface, *can* allow a primer to extrude and expand before the casehead moves fully back. Primers under these conditions can appear flattened or mushroomed with loads that are well below maximum specified pressures.

3. The same observation can be made regarding primer "cratering". Most often, excessive clearance between the firing pin and the firing pin channel at the boltface/breechface can result in primer metal being left in a raised ring above the rest of the primer. This can happen well below maximum specified pressures.

4. Virtually every other "pressure sign" such as sticky extraction will usually appear well beyond max-spec pressure loads.

5. No one appears to have reliably gaged the effects of "softer" brass on "pressure signs" like brass extrusion into unsupported areas of the casehead (ejector holes or grooves, etc.). Without data which includes chamber pressure AND the make of brass (including the BHN or other hardness measurement), most discussions of this pressure sign are of little guidance.

6. Measuring casehead expansion in high-pressure rifle rounds can identify chamber pressure levels which coarsely approximate factory loaded rounds (presumably within specs), but is most reliable using unfired cases of the same brand. Much more data for once-fired cases is needed before this method has a hope of doing anything other than identifying loads which are an unknown pressure level ABOVE safe.

7. IME, no one who preaches pressure signs as a reliable way to establish a max load in *your* firearm has been able to authoritatively say how far a reloader must "back off"{ of the pressure-signed load to return to safe pressure territory.

8. IME, loading to reloading manual max velocity for that exact same bullet, in that exact same case, with the exact same powder, and the exact same barrel length, is the only method to be trusted. There *may* be a +/- 100 fps tolerance for "fast" or "slow" barrels (I've had both) built in here, but further reliable study and data is needed.

I'm done.

 

[Grump]

That's simply NOT so! The SAAMI specifications are no more than an AVERAGE pressure limits and a reasonable guide. But, it's NOT an absolute point that can't be crossed without the hazard of death and is quite safe if we stay under it. Again, history's experience and our loading manuals confirm that.

Do you even KNOW the different types of "average" pressures for which there are SAAMI standards? It's not just one number for each cartridge.

In many ways, it's like that pesky speed limit. You can exceed it every day for decades without death or injury. But if something else goes wrong, like a tire failure or some clown clipping your bumper in a lane change, what could be easily survivable at 75 mph just might smear your brains all over the pavement at 85 mph.

How much of *your* safety margin do YOU want to "spend" each day?

 

[ranger335v]

"Do you even KNOW the different types of "average" pressures for which there are SAAMI standards? It's not just one number for each cartridge."

Grump, no I don't. Nor, as I'm sure you are aware, no else one quite knows what pressues are built when we fire a round. That's part of why I don't think any SAAMI spec is absolute gospel. It's generally accepted that neither CUP nor PSI are anything more than approximatations even tho they are the best we have now.

But, the question remains, by what gage does something suddenly become unsafe? None of us seek to be unsafe but perhaps the only way we can be absolutely certain we are safe could be to limit all (riife) chamber pressures to perhaps 30Kpsi; that would be safe, right? But it would also waste a LOT of user potential too! Saying we "can't be too safe" can be taken to such silly limits that we couldn't do anything. And it would be to attempt to load an early 30-06 Springfield '03 to 55 Kpsi, what is generally considered quite safe in more modern rifles, even tho SAAMI says it should be safe.

The issue here is, "What determines what is actually safe?" Is it the ability of the weapon AND cartidge to easily withstand the presssure or is it 55 or 60 or 65 Kpsi and no more? I say it's the combined combonation of the cartridge and action to retain the pressure, not some line drawn in the sand, so to speak. We had better know what we are doing, and how to keep track of its effects because no book can guide us with any high degree of accuracy. BUT, understand that I am NOT saying to ignore the SAAMI pressure guidelines, I'm only saying to use them rationally. And without playing Chicken Little!

Anyone doubts his ability to "read pressure signs" better stick with book loads. But then my buddy that gets blown primers in a near new Mod. 70 with mid-range charges of Varget in .22-250 would say you absolutely can't totally trust the books either! NO, I don't know what pressure that load was but we both can read pressure signs well enough to know that load was much too hot, no matter what our load manuals say!

Knowledge of what we are about, and good judgement keeps reloaders safe. Blind, irrational fear of a table of numbers does not.

 

[.38 Special]

Ranger, IMO you've got your toes right up to the "strawman" line. Nobody is saying that SAAMI standards are "absolute gospel". They are, however, standards put together by people who, frankly, know more about the subject than you and I. My argument remains that the pressure guessers are fooling themselves if they think they can use SAAMI specs as "suggestions" or "guidelines" -- especially when they strike out on their own to determine for themselves how much pressure their pet rifles can take.

 

[.38 Special]

Let's try a few theoreticals for those with advance abilities to read the signs:

You have a rifle with a very rough chamber. The mildest loads in the books work fine, but even the low-middle loads produce difficult extraction. Are those loads dangerous?

You have a rifle with an extremely smooth chamber. It does not show signs of sticky extraction even with loads exceeding the book maximum by 20%. Is this load dangerous?

You have a rifle with hand fitted lug recesses. The bolt can be lifted with one finger after firing SAAMI proof loads. Is this load safe? How many can be fired in the gun before metal fatigue becomes a factor?

You have a rifle with uneven lug recesses, but still within factory tolerances. Bolt lift requires force even with factory loads. Is this rifle dangerous for use with factory loads?

And one more: what if you change primer brands in that Varget load that blows primers, and the new primers hold up just fine? Do you assume that pressures changed? Or do you assume that primer cup thickness made the difference? Do you actually know anything about the pressure of either load? Is one more or less likely to blow the action?

 

[ranger335v]

Actually I've lost interest. You have steadfastly ignored my questions and still haven't yet said what you really believe is "safe." But, it don't really matter, do it?

Example: " Meanwhile, there is absolute proof that a load can demonstrate no pressure signs while exceeding SAAMI specs by a wide margin." You haven't said it but, I will ask again, does it follow that SAMMI ammuniton specs are, by themselves, the guide to what is "safe", regardless of how well the weapon and case are performing? Disregarding completly how well or poorly designed and made the weapon it fired in is? Meaning safety in a load is dependant on an abstract pressure number, standing in isolation?"

I give up, why bother trying to discuss anything with a non-responsive poster?

Now, your new "hypothetical" questions are unreasonable, to the point of being silly. The man's primers aren't pierced, they are "blown", technically meaning the primer falls out of an expanded pocket. No real "max" load + 20% would allow the bolt to be opened with one finger. The rough chamber question is foolish, etc. All nonsense.

You certainly do, by implication but still without clearly stating anything, strongly suggest that you believe SAAMI specs absolutly define what is or is not safe. Or maybe it's your writting comprehension.

You simply show no acceptance that reason can come into play with book loads, including no response to my example of a low number 1903 Springfield or a Ruger#1 in .45-70. You simply refuse to say or't define what you do mean, leaving me nothing to work with!

It appears you aren't interested in a dialog, only in argument. I'm not. So, have a blissfully happy day. :banghead:

 

[jon_in_wv]

It appears you aren't interested in a dialog, only in argument.

It does appear to be his pattern if you look at some of his other posts.

 

[.38 Special]

Actually I've lost interest. You have steadfastly ignored my questions and still haven't yet said what you really believe is "safe." But, it don't really matter, do it?

I've answered all of your questions that I am aware of, and I have given my opinion of "safe" throughout the thread.

Example: " Meanwhile, there is absolute proof that a load can demonstrate no pressure signs while exceeding SAAMI specs by a wide margin." You haven't said it but, I will ask again, does it follow that SAMMI ammuniton specs are, by themselves, the guide to what is "safe", regardless of how well the weapon and case are performing? Disregarding completly how well or poorly designed and made the weapon it fired in is? Meaning safety in a load is dependant on an abstract pressure number, standing in isolation?"

No, it follows that a rifle in good condition is almost certainly going to be safe with published maximum loads. A rifle that is not in good condition is probably not safe with any loads. And the idea that SAAMI numbers are "abstract" is startling to me. Do you really believe those numbers don't have a basis in reality?

I give up, why bother trying to discuss anything with a non-responsive poster?

IMO you have mistaken "responsiveness" with "agreement". I think you are wrong and I am trying to demonstrate it by responding to your posts.

Now, your new "hypothetical" questions are unreasonable, to the point of being silly. The man's primers aren't pierced, they are "blown", technically meaning the primer falls out of an expanded pocket. No real "max" load + 20% would allow the bolt to be opened with one finger. The rough chamber question is foolish, etc. All nonsense.

I was unaware that there was a dictionary definition for "blown" primer. I have personally seen rifles fired with SAAMI proof loads that showed no signs of pressure whatsoever, including sticky bolt lift. And I personally own a rifle with a chamber so rough that sticky extraction occurs with starting loads. If this is all "foolish nonsense" -- nice effort at "dialogue", BTW -- then it should be simple for you to explain why.

You certainly do, by implication but still without clearly stating anything, strongly suggest that you believe SAAMI specs absolutly define what is or is not safe.

I'm not implying anything. I am clearly stating my position. Anything else you are reading into it is your own problem.

Or maybe it's your writting comprehension.

When making fun of your interlocutor's intellect, it's generally a good idea to spell it right. Not that that particular insult makes sense even when spelled correctly...

You simply show no acceptance that reason can come into play with book loads, including no response to my example of a low number 1903 Springfield or a Ruger#1 in .45-70. You simply refuse to say or't define what you do mean, leaving me nothing to work with!

And yet I'm the one with the comprehension problem...

It appears you aren't interested in a dialog, only in argument. I'm not. So, have a blissfully happy day.

Pot, kettle, etc.

 

[jon_in_wv]

Nor by attacking other posters, attacking thier preferences, childish slams at their opinions, or total disrespect. You should heed your own advice.

 

[.38 Special]

Do you have anything to contribute, Jon?

 

[RoostRider]

Seems like you guys are taking this a little too far....

Leaving our safety margins intact can prevent such things. Pushing them makes no sense, considering -- yet again -- that if you need a bigger cartridge you can almost always address the need by buying a bigger cartridge.

Thats what I was thinking.... I have a .223 to do the things that a .223 does well.... and a .308 for the things it does well.... I didn't buy a snubbie .38 thinking "oh well, I can load it to .357 power"... I bought the snubby for what it does well (carry around).. I bought a +P capable gun, because I wanted all the 'edge' a .38 spcl. can give.... I load to ~+P and call it good... I usually test a few a little 'hot' just to see (taking into consideration the gun of course)

That being said, I don't push pressure too high, but I have been known to work up a load over the manual using pretty much all of the 'guess' methods together.... I know it's not foolproof but I also know the gun in question and the cartridge are capable of going over the top as far as the manual is concerned... eek it over a little bit, test a few rounds, check for signs, call it good for 'tops' out of that cartridge...

I think the trick is not getting carried away with what you want out of your gun... and changing guns if that is what you need...

Why would someone push the limits of a gun/cartridge 's capability by foregoing reasonable safety margins? but I also think the realistic margins are different for different guns... brass failing is one thing (and clear evidence of something way out of whack), but your barrel failing is a whole nother... just get the right gun and be safe...

Unless, of course, we are talking about a testee's issue (double meaning intended.... get it?... lol... I kill me)... and the real issue is to push something further than it is supposed to go.... then by all means.... just don't stand near me at a range and 'test' your theories.... *that's what worries me most....

Hope I haven't pissed anyone off here.... since I kind of agree with both takes... lol

 

[.38 Special]

FWIW, I'm not arguing that exceeding manual maximums automatically puts you into danger territory. If the max is 50 grains, 51 grains isn't likely to be disastrous -- especially if you are simply attempting to get your bullet up to advertised velocity.

It's the folks that argue that the manuals are all put together by lawyers and view pressure data as mere suggestions; that figure they'll just add powder until something bad happens and then back down just until the bad stuff goes away, that I think are flirting with disaster. This seems to be fairly common, as evidenced by threads like this one.

 

[ranger335v]

"I was unaware that there was a dictionary definition for "blown" primer"

Interesting admission. Yes, there IS a commonly recognised "dictionary definition" of a blown primer, it's clearly definened by the highest photo in post #10.

Your obvously great knowledge has covered significant gaps, making you fail to see there's a lot you are unaware of. But it really makes no difference does it? Nor do Ad homanum (sp) slurs matter at all, it's all in fun, right?

(What you have posted so far makes no real sense!)

 

[USSR]

FWIW, I'm not arguing that exceeding manual maximums automatically puts you into danger territory. If the max is 50 grains, 51 grains isn't likely to be disastrous -- especially if you are simply attempting to get your bullet up to advertised velocity.

Ha, that's choice, .38 Special. When I listed my handload that is 0.7gr higher than a published load, here is what you had to say:

The poster who goes by the screen name of "USSR" uses old wive's tales in lieu of pressure testing equipment, and also has the habit of recommending dangerous reloading practices to people who may not be experienced enough to recognize the hazards therein.

followed by:

I've just been informed by a moderator that I am brushing up against the rules here. Apparently it's okay to recommend that users blow themselves up, but not to suggest that they don't.

As previously stated, you only come on THR to argue, and you trash anyone that stands up to you. So, reload the way you want, and just leave us guys with more experience than you the h~ll alone.

Don

 

[.38 Special]

No, Don. You're playing games. The line you quoted was not in response to you exceeding max loads by .7 grains, it was in response to you claiming that one can safely ignore max loads if you pay attention to pressure signs.

In all the responses you have made to me -- including all the personal attacks -- you have never actually addressed any of the points I have made re. the uselessness of reading pressure signs.

Between you and ranger, I'm getting an earful of "You're making personal attacks" along with "You're a big doodoo head", and "You don't answer any of my questions" along with "I'm not going to answer your questions". Which is amusing, if not terribly productive.

So, anybody want to talk about the thread topic?

 

[.38 Special]

"I was unaware that there was a dictionary definition for "blown" primer"

Interesting admission. Yes, there IS a commonly recognised "dictionary definition" of a blown primer, it's clearly definened by the highest photo in post #10.

You're right. That is "a" definition. The trouble is that it's not "the" definition, and I have heard the term used in reference to pierced primers many, many times.

The difficulty, it seems to me, is that you are more interested in scoring points than addressing the thread topic. Not much I can do about that, I guess.

 

[Gryffydd]

This is awesome. OP starts a thread with a post that's basically stating the obvious, but slightly misguided, very condescending and pretty much irrelevant--for the specific, admitted purpose of stirring things up. Then accuses others of only trying to score points rather than contribute to the conversation.
Thanks for the entertaining thread