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THE LEAST RELIABLE "PRESSURE INDICATOR"




In his classic 1947 book Hatcher's Notebook, recently retired Major General Julian S. Hatcher wrote about his almost 40 years in the U.S. Army involving various aspects of firearms from handguns to artillery. Hatcher had an enormous amount of experience, including developing a solution to the brittle receivers of early 1903 Springfields, a simple hole drilled in the receiver to relieve gas pressure from blown cases. After retirement from the Army, he spent a number of years on the staff of the NRA's magazine American Rifleman, where he provided technical information on new developments in sporting arms and ammunition as well.

Hatcher's Notebook has been reprinted numerous times, because it contains a wealth of information still very pertinent today, including this comment:

"In the years just before World War II, it became the fashion for gunsmiths all over the country to originate 'wildcat' cartridges by 'improving' some factory cartridge, and then giving it a fancy designation with the originator's own name added.... Usually in the process the shoulder was made considerably sharper than it was in the original....

"Making the shoulder sharper does, of course, add powder space, and thus make possible higher velocities, accompanied of course by the inevitable higher pressure.... Very carefully conducted experiments, using chronographs and pressures gauges, with cases of the same caliber and cubic capacity, but with shoulders of different slopes have failed to show that the shape of the shoulder makes any difference at all.

"Usually the originator of one of these cartridges had no facilities for taking pressures, so depended entirely on the notoriously unreliable method of judging pressures by the appearance of the primer."

Now, this was written by a man who'd spent decades using the best testing equipment then available. So why do so many sources of handloading information, including loading manuals published by major companies long after Hatcher's Notebook appeared suggest primer appearance as a valid pressure sign? In fact, one such manual was published in the 1960's by a bullet company that purchased pressure-testing equipment but apparently couldn't figure out how to use it. Instead they depended on primer appearance (and other such seat-of-the-pants signs) to work up their published data, with absolutely no verification of the actual pressures.

Unfortunately, Hatcher did not explain his statement in the Notebook; otherwise millions of handloaders would have quit wasting their time "evaluating" primers. But by reading other sources, including American Rifleman (my collection goes back to the late 1920's), here are some of the reasons:

The major pressure-indicator is supposedly how much the surface of the primer flattens during firing. This flattening occurs because as pressures build inside the case, the gas not only pushes the bullet down the bore, but pushes backward through the flash-hole against the expended primer, forcing it against the bolt-face/breechblock. The impact flattens the thin cup of the primer. (In fact, the pressure starts the primer moving backward before the bullet starts moving forward, because the powder immediately in front of the primer obviously ignites first.)

There are several reasons flattening doesn't work reliably as a pressure sign. First, different rifle primers have cups of different thickness. Second, while they're normally made of the same brass used in cartridge cases, about 70% copper and 30% zinc, the ratio can vary somewhat, just as it does with cartridge cases. Both thickness and the specific brass can result in a different amount of flattening.

Also, relative primer flatness can be affected by even a slight amount of headspace, the distance from the rear of the case and bolt face/breechblock. If the pressure's below about 45,000 PSI, the primer won't flatten much as its pushed backward in its pocket by expanding powder gas. Plus, unless the chamber's well-oiled, the relatively low pressure isn't enough to push the case back against the bolt face/breechblock, whether through sliding or stretching. Instead the case sticks to the chamber walls, and the primer remains slightly backed-out of the case.

This is common in the .30-30 Winchester, because the SAAMI maximum average pressure is only 42,000 PSI. The standard SAAMI maximum headspace allowance for just about all centerfire rifle cartridges is .007 inch. This may not sound like much, but when a primer backs out that much it's easy to see.

In higher pressure cartridges, from the .22 Hornet (49,000 PSI) on up to the maximum 65,000 PSI allowed by SAAMI for any rifle round, the pressure does push the case-head against the bolt-face/breechblock--unless headspace is absolutely minimum, often due to neck-sizing after being previously fired in the same chamber. Generally, full-length-sized cases will have a little headspace, and obviously new cases (the kind many handloaders use to start working up loads) may have up to .007 inch.

This results in the primer backing out first, whereupon the rear of the thin cup expands sideways slightly, because it's no longer supported by the primer pocket. As pressures continue to rise, the case backs over the primer cup, and the slightly expanded brass at the rear of the primer cup is squeezed back into the primer pocket. This results in the primer appearing VERY flat, even at relatively low pressure.

This "false flattening" can also be enhanced by the edge of the primer pocket. Some pockets have considerable radius at the edge, while others are relatively sharp.

Three other commonly advised primer "pressure signs" are a ridge around the firing pin indentation (where the primer brass flows into the pin's hole in the bolt face/breechblock), a pierced primer (where the firing pin indentation blows out), or a leaking primer (indicated by black residue around the edge of the primer).

Unfortunately, like primer flattening all three can occur because of factors other than excessive pressure. Many rifles have rather loose firing pin holes in the bolt face/breechblock, allowing primer brass to flow into the hole around the tip of the firing pin. A weak firing pin spring can also result in the same "false positive," and both effects can be enhanced by thinner/weaker primer cups.

A pierced primer can easily occur when the tip of the firing pin is too pointed, and primers can leak around the edges due to brittle or cracked primer cups, especially where the cup is "folded" during forming along the corners. Again, high pressure doesn't necessarily have anything to do with the piercing or leaking.

The other factor in all this, of course, is most handloaders (like the aforementioned bullet company) have no way to actually measure pressure. As a result, they have no idea whether any of these mystical pressure signs are valid.

The one sure primer pressure sign I've encountered during decades of handloading rifle cartridges is a primer that disappears during firing. This is known as a "blown" primer, caused by pressures so high the primer cup disintegrates, because the primer pocket expands so much it's far larger than the primer. This takes a LOT of pressure, and I've only seen it a handful of times, including (more than once) with factory ammo. Only two primers were blown by a mistake on my part, both caused by assuming too much, and I've NEVER repeated either mistake again.

Nice writeup, JB. Maybe you've made headway in killing off the notion that primer appearance can be read as a pressure sign. Hard to slay some of the old lore that persists, though.

Good information. I should tape it to the loading bench.

The one point you quoted from Hatcher that I am not clear on is that shoulder shape has no affect on pressure. Maybe in regards to high or low pressure but I thought and you have stated that the 30 degree shoulder appears to produce more uniform pressure according to the ballistics labs.

The same on case shape, no difference, but then some claim a shorter powder column is more uniform.

Also how does this relate to bushed firing pin holes and small rifle primers showing (producing?) less pressure? Lots of questions left for Gun Gack III.

Given the equipment of the time Hatcher could not report on shot to shot variation with the precision that a lab can today, and I wouldn't think he could have looked at a time-pressure curve for an individual shot at all.

The average pressure produced by two cases of the same capacity will be the same, but the other statistics may vary.

Your average Joe would trust a credentialed army general, especially one who worked in the Ordnance Corps. Much of it can be attributed to the time. That included a lack of test equipment and new low and high explosive compounds developments that were not fully understood by users. And of course, when an officer, especially a senior one, renders his opinion, he is rarely questioned.

What were General Hatcher's credentials? I know he graduated from Annapolis, but I wonder what he studied? Was he an engineer? You see this, but it really doesn't say anything.

"Julian Sommerville Hatcher was a noted firearms expert and author of the early twentieth century. He is credited with several technical books and articles relating to military firearms, ballistics, and auto loading weapons."

Bushed firing pin holes reduce "blanking" of the primer cup material into the hole. They do not change the pressure at all.

John, good write-up. I have a question. Many years ago, someone (can’t remember who) was selling a “strain gauge” for measuring chamber pressures. What ever happened to this product. Not reliable, too expensive, etc.? Thanks! memtb

Google "pressure trace."

See e.g. the thread on this board #942440 - 07/27/06 RSI Pressure Trace and Chrony 5 pages of running on as is typical on this board. Tooling is still available. Reliable in the sense of consistent measurements and affordable for limited use. Discussion by Ken Howell, RockyRaab, John Barsness, Denton and others including more reliable like those cited and others.

IMHO the major issue is calibration so that strain gage readings can be crossed to psi measurements. Secondary issues associated with barrel vibrations and maybe resonance have given some confusing results with multiple pressure peaks.

As I read it Ken Oehler suggests the set up would be better with a proof channel. That is there are as many questions as answers and this has kept the system from sweeping the field.

Very article, MD. I particularly liked the last sentence..... Been there done that as well. At least I discovered why mauser extractors are so popular. In both cases, one was a tang safety Ruger, and the other a 98 mauser, the action could extract the cases without pounding the bolt with a mallet. E

I have a Remington 7 mag that will flatten primers ( federal) even with starting loads. They chronograph normally and do not show any other pressure signs. I assume its because of soft primers.

Interesting read.

Something I have noticed lately is in seating primers. I have always swiped my thumb across the primer after seating and 'felt' for them to be properly seated. But I was having a few rounds that would chamber slightly stiffer than normal. I believe that was caused by the primer not being completely seated. I have since been seating the primer then laying the case (primer down) on the back of my dial caliper (nice flat surface) to verify the primer is fully seated. I have been surprised at how often a primer is not fully seated and will rock back and forth on the caliper. This may also contribute to the primer flattening?

I have a problem with that statement. The pressure inside the case is equal in all directions.

I have a Remington M700 BDL in 30-06 that will give a cratered primer with just firing an empty primes case. I bought the rifle NIB from a department store that was going out of the sporting goods portion of their sales. On close examination with a magnifying glass, one can see where the firing pin hole has a slight chamfer. Actually you can see it without the glass but it just makes seeing it in better detail. I've run some pretty stiff loads though that rifle and other than that cratered primer there's been no problem.
Paul B.

Comments so far:

MartinCreek,
In general, Federal primers often do flatten more than CCI, Remington and Winchester primers, because their cups can be thinner. In fact, I've owned both a rifle and a revolver that would go bang consistently with Federal primers, because the cups were more easily dented by the firing pin. It turned out the mainspring on the rifle was going bad, and eventually it wouldn't make any primer go bang. The revolver was a Ruger Redhawk with a "spring kit" installed, which made the trigger pull a lot better but also made Federal primers necessary.

Centershot,
Protruding primers just might contribute to flattening! (Now I might have to run some experiments.)

Muskegman,
Yes, the "pressure inside the case is equal in all directions." But that is true of the eventual maximum pressure. Initially, pressure always finds the path of least resistance.

In this instance that's through the flash-hole, rather than at the other end of the case where the bullet starts moving. Even in very small calibers, the bullet is not only heavier than the primer, but usually held far tighter by the case neck, because of more contact with the neck and, sometimes, crimping. (It takes a lot more force to seat a bullet than a primer.)

Plus, the normal "high" primer of fired .30-30 cases indicates the primer was backed out the initially relatively low pressure.

What a coincidence...This week, I brought "Hatchers Notebook" as reading material for my long flights. Rereading this book never gets old. New things stick in my brain each time.


Ken Oehler offered his M43 PBL, which to my knowledge was one of the earliest consumer oriented pressure testing units. Around the same time Steve Faber also produced one. Both are strain based and preceded RSI's Pressure Trace.

OH but MD...............whatever happened to "all other things being equal?" when it comes to things you DON'T push.

LIKE the 4-1 "rule" (very weak guesstimate that originated in the 60s by Homer Prowley with the ALSO antiquated "Prowley Computer" where it DID actually give SOME information because IT WAS APPLIED TO CAPACITY INCREASES MADE IN THE CHAMBER OF THE SAME RIFLE, WITH THE SAME BARREL, WITH THE SAME BULLET JUMP, SAME SEATING DEPTH, SAME EVERYTHING......EVEN THE SAME POWDER")

Back THEN........it was "about", "kind of close", "in the area of"........this much increase in velocity. Comparing rifle to rifle? Cartridge to cartridge" Regardless of ALL OTHER FACTORS that make UP a rifle.......is ludicrous.
Until EVERY rifle shoots the velocity given IN the compared load data used in the aborted version of the "4-1 rule"........it is entirely, absolutely, and without a doubt.............POINTLESS.
Going from factory barrel to a decent custom barrel can give you up to 100 fps........or more, alone, depending MUCH upon the very, very, very small changes/differences in bore/rifling diameters. Being BETTER barrels as far as accuracy goes is NOT the only differences.

Anyone doubting this please compare Nosler's load data pages to the Hodgdon reloading data site. Compare the same powder, same bullet (you have to look some), same barrel length and see how often (almost always) the Nosler data is way more (often 100 fps plus) than the Hodgdon data. They look at the name NEXT TO the barrel length on the Nosler site. Nope..........."all things are not equal".

Comparing two rifles...........THEY ARE NEVER EQUAL. There does not exist a "rule of thumb" on how high or low the velocity/pressure/accuracy/anything else compares. Trying to create one is a waste of your time and thought processes. Your rifle, your brass, your powder and primers, your efforts as a hand loader, make every combination an entity of it's own right. No one, no data, no arbitrary "maximum pressure" applies. It's safe in your combination........or not.


The information given here in the OP is OLD...........OUTDATED..........and NOT comparing primer to primer fired ALL OTHER THINGS BEING AS EQUAL AS POSSIBLE..........makes it all worthless..

No, all things cannot be equal.........ever, but handloaders SHOOT FOR such for low ES and low SD, (as consistent as possible) and DO use primers as a half decent high pressure sign.............because it is when the person loading makes all efforts to properly load rounds (as close to identical as he/she is able) , firing them in the same chamber (that they KNOW is clean and dry) .
Every long range competition shooter KNOWS the "weak link" in high pressure loads............is the soft (by comparison because it is not SOLID metal and not the same thickness as case base material) and it is PRESSURE FIT into the case. What gets pushed IN can get pushed out.......if there is "room" (bad sizing) but if not..........the primer TRYING to push out enough to deform it......IS HIGH PRESSURE.

Many studies have been done by competition long range shooters on primer hardness and size for that very reason.
Proper primer fit, proper case to chamber fit, headspace etc etc is a "surely you are doing that" kind of thing because experienced hand loaders know this is the main key to consistency along with the same components. They are not mentioned because it would be an insult to the other person asking them if they knew what the H they were doing...........just not saying it straight out.

What also gives "high pressure signs" in loads/chambers/ etc concerning improper care or loading............is moot and does NOT take away from the fact that ...............if you get primer deformation in loads you know for a fact are as equal as possible........and then you back off a half grain and you DON'T have primer deformation.......................IT WAS HIGH PRESSURE. (Talk about a no-brainer).

*******A short word (oops.......too late for that,eh? LOL) to those here that can think for themselves. READ the pages before and after SAAMI "Maximum Average (repeat AVERAGE!) Pressure" charts. I'm not going to tell you what they say. I have complete faith that those who understand the English language and will take the time to read through it all..........will see some BLATANT differences in what is tossed about. Special attenton to WHO SAAMI IS, What they can and cannot do.......and do not set!, How testing is done. What factors can cause errors in their tests (any anyone else's!!).

On pressure..........look ESPECIALLY for a statement on "97.5 percent of the service rounds will not exceed WHICH Maximum? and last but oh so far from the least.......Look for the STANDARD OF DEVIATION for their MAP findings. AND ALL THE OTHER PRESSURES within their report!.

Take the "Maximum Average Pressure" out of context and deciding what it is or is not, is like reading the 10 Commandments ( Exodus 20 KJV version) and seeing "Thou Shalt Not Kill" ..............and deciding to sell all your firearms because of what that "means".

Forget what you've been told.......read it all and read it again. Then give thought to this....... When you understand what the REAL maximum pressures THEY PREDICT are within FACTORY ammo, recall how often you have seen a rounded or flattened primer using them (it happens.........rarely) ...........then rethink what pressures WE are at when we sneak up on max (FOR OUR RIFLE) but back off when we get to pressure signs. Especially when you realize where your pressure MIGHT be when you see for yourselves the standard of deviation on chamber pressure ESTIMATES. And yes........all means of measuring chamber pressure have one. And yes............the Piezoelectric testing is considered one of the most accurate.
That's why SAAMI uses it. (I'm sure SOMEONE will huff and puff about the "strain gauges" now........oh well. YMMV?)

I'm not attempting to get people to load hotter............I'm trying to get people to think and decide for themselves. (Yes MD we KNOW........."You load to velocity"...........gimme a break.)

MODERATORS! While I would love to have a decent conversation on this, I will not return to reply on this post. The blatant disregard for controlling insulting, idiotic ramblings on this site make it of no interest to me ..............what-so-ever.

Hint.................


My apologies to those having a true interest in finding out for themselves (aka thinking) for my poor writing abilities and the mis-spelled words. I don't have multiple people proof-reading my work, plus it's just past 2AM. I only hope I've reached............at least a few.
YOU GOT THIS! You don't need MY or "anyone else's" help.

Have at it bashers. I can insure you that, I for one, will not waste my time reading them.

Oh.........MD? YOU owe Homer Prowley a public apology for aborting something he offered us into the lunacy you've stated as any kind of useful information. I mean............come on. Buy five rifles, all in the SAME caliber and they won't often shoot within a 50 fps span of each other. Guesstimating velocities CARTRIDGE to cartridge ALSO in differing rifles?..............zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz.

God Bless. Hunt safe.
Steve

Am I the only one looking at this post thinking, "What the hell is all this pointless rambling"? I believe that I'll take John's side in almost every case (although I'm still not a fan of NBT bullets, but experience is limited to .25 caliber), due to his extensive testing, research, and thoughtful analysis. He also has no problem telling us when he's discovered, through trial-and-error or learning from other professionals in the firearms/ammunition/reloading industries, that what he has thought to be true isn't necessarily so. Guess he never thought of himself as a scientist, but he does use scientific principles to arrive at his conclusions. So, Steve....

Agree. I found myself wondering what Steve's point is also.

Dunno either, and can only guess at what Steve's point is about Homer Powley and the 4-to-1 Rule.

For those who aren't familiar with it, the 4-to-1 Rule is that any increase or decrease in the powder capacity of rifle cartridges of the same caliber results in about 1/4 that amount of potential velocity, with the same bullet at the same basic pressure. One example I've used frequently is the .300 RUM and .308 Winchester: The .300 RUM has just about twice the powder capacity as the .308, but does NOT produce twice as much velocity--a 100% increase. Instead the velocity increase, with the same bullet at the same pressure, is about about 25%, which is 1/4 of 100%. This rule does not apply to the SAME powder, but the powders producing the highest velocities in each cartridge.

I am quite familiar with Homer Powley's slide-rule calculator, having purchased one around 40 years ago--and still have it in my bookshelves, packaged in a manila envelope with all the accompanying literature. Can't figure out what the 4-to-1 Rule has to do with any of Powley's basic rules, except that it's another phenomenon derived by crunching the numbers from LOTS of pressure-tested data.

The only similar rule I can remember from Powley is that pressure with single-based powders increases at twice the rate of velocity--which might be called the 2-to-1 Rule. But that was derived from copper-crusher pressure data, not the piezo-electronic data used by the best pressure-labs today, which shows the velocity-pressure relationship isn't quite that simple, even with single-based powders. It varies even more with double-based powders.

Steve also seems to be arguing that pressure-judging by primer appearance works very well. Would love to hear if he can supply some data. I seem to remember Denton mentioning that he'd tried it, and found no correlation.

Well, I'm going to respectfully disagree again. There are two forces at play to get either the primer or bullet to start moving - (1) you have to overcome the static friction holding it in place, and (2) you have to overcome the inertial mass. The primer starting to move first is because the force holding it in place (friction) is lower AND the inertial mass is lower. It's not because the pressure is higher down near the primer.

Where's Denton when you need him?

I did NOT say "the pressure is higher down near the primer" I said the powder starts to burn there, so the hot gas expands through the flash-hole quicker than through the neck at the other end of the case. Plus, the primer is obviously easier to push backwards, the reason fired .30-30 cases often show "high primers."

Just because the peak pressure is evenly distributed throughout the inside of the case doesn't mean pressure doesn't affect everything in the same way during the initial powder burn.

Apparently, the Steve to which you are referring is not me.

Still, I am sorry that i did not preface my post with a brief explanation. I was attempting to point out that it was hard at that time to keep up with the science. It was evolving quite quickly. Much like electronics and computers are changing now.

For example, I was thinking that Hatcher's work (and the work of others) was done before test equipment or methods had been devised or refined that could accurately determine over pressures within a case. Some things that people of the time believed have since been disproven. Using primer flattening or expanded bases might have seemed like a logical conclusion then, and few would have questioned it. Hatcher worked for the Ordnance Corp and his opinions were respected, and deservedly so. But science is always advancing, both the methodology and a better understanding of the chemistry.

Explosives and the science that explained it were advancing almost daily at the beginning of the 20th century. I have said this before, but in a very short time, we went from primitive single shot mechanisms using BP and firing lead balls, to smokeless, repeating firearms firing jacketed bullets, tracers, etc. It would have been an interesting time in which to live. What you learned in university was quickly eclipsed by new science.

Men like Hatcher worked for the Ordnance Dept for over 40 years and they saw a lot of changes. I think Hatcher and others can be forgiven if they didn't get everything right. Their work advanced our understanding of ballistics.

Steve,

That particular post was directed toward Steve692.

Would love to hear if you have evidence that Hatcher was wrong about primer appearance. None of the piezo-lab people I've talk to believe he was, for the reasons stated in my article: There are too many variables in primer cups, and other factors such as headspace, bolt-face, etc., for primer appearance to work even as a rough "estimate" of pressure.

Which is why I ran experiments on such traditional pressure signs with the help of one of those piezo labs over 15 years ago. One .270 load averaged around 69,000 PSI, with some of the individual shots over 70,000. Yet the primers appeared completely "normal," just as normal as the primers used in a .30-06 load that averaged 58,000 PSI.

In fact the only "pressure sign" that followed the piezo results was velocity.

That's out of my area, John.

If I was attempting to determine that primer appearance was a reliable indicator, it would be necessary that absolutely everything was uniform, test to test. All the components of the test cartridges, the firing mechanism, etc. In other words, you would have to positively eliminate differences in propellant/primer composition, case construction, ambient temperature differences, use a single test mechanism, etc. That's an awfully tall order. Temperature and pressure would have to be constant, cartridge to cartridge. If you could manage that, then change one thing at a time to see how much of an influence that change had.

I don't see how that could be done with our present technology.

True, you did not exactly say that. You implied that pressure is felt on the primer cup before the bullet base because the powder starts burning (resulting in expanding gas) closer to the primer.

This implies that primer moves back first because it "feels" pressure buildup first (before the bullet feels it). I don't think that's the way things work . . .

Steve,

I have provided several examples of how primers can give "false positives" of too-high pressure, and one example of a "false negative."

The exact sort of test you are describing occurs all the time in piezo labs, in very controlled conditions. If primer appearance (or even measurement) provided a valid measurement of pressure, why would professional labs go to all the trouble and expense of purchasing all that expensive equipment?

MuskegMan,

The primer doesn't "feel" anything. Instead, the flash-hole is just the first "escape channel" for hot powder gas, just as the lowest point in river levee is the first for high water.

Once again, the reason primers back out very early in the build-up of gas-pressure is because they're far lighter and less "tight" than the bullet. I already gave you a very graphic example with .30-30 ammo--but a less obvious example is MORE primer flattening in new brass in higher-pressure cartridges. That occurs because there's often a little more headspace with new brass, again because the primer backs out before the case starts to expand. If the same load is fired in once-fired, neck-sized brass, the primer won't be nearly as flat.

Not a strain gauge system, but I was always intrigued by the York-Cantrell "system".

John, they wouldn't. Labs follow a scientific method. Have you seen anything that indicates they have been successful following a particular metric?

Steve,

Their methodology is all laid out in the SAAMI testing protocols. You can see them on the SAAMI site--but at least one lab I've worked with considerably runs their own experiments now and then.

I know, John. They keep testing to verify and advance the science. Because I never worked in development, I have relied on the testing that the powder/explosives companies employ and trust their data.

I only worry about pressure when I'm testing new powders. Then, I depend on my chrono. Some might call me naive, but pressure and velocity are closely tied together. I never worry about primers because I was told years ago, despite due diligence, things fail from time to time. They are the exception, not the rule. Try not to worry about the "what ifs".

Might also mention that have had extensive conversations about copper-crusher testing with pressure labs, because even as major labs have converted to piezo, they have plenty of copper-crusher barrels on hand. which some still use for cartridges that aren't all that popular, because it doesn't make sense to build/buy a piezo barrel. The main comment from the head guy at one lab was that copper-crusher barrels provide good overall pressure data (though not as precise from shot-to-shot, pressure-curve) as piezo barrels.

But the biggie is takes a lot more time to do the prep and post-work work for a CUP test. It takes far longer than most shooters would imagine just for a valid for a piezo test, including far more expensive equipment, but not nearly as much time as with CUP equipment, mostly because of all the measurements involved.

Yes, Hatcher did use copper-crusher equipment, which was state-of-the-art in his day. But it was perfectly capable of providing results to come up with conclusions about pressure and primer appearance.

I have never had a blown primer or stuck case. Thanks to Muledeers information that I gleaned years ago about useing a chronograph and velocity as a pressure indicator I may very well make it many more years to come. Thanks Muledeer!!! No doubt I've been fortunate and probably some luck involved but good information goes a long way toward helping


Trystan

Trystan,

Good to hear the chronograph has provided reliable results!

Question - Does anyone know if Hodgdon uses the copper-crusher or the piezo-electronic method for measuring pressure for the 257 Roberts? Their site shows CUP but is that really how they test?

It means copper-crusher is how they tested the data listed.

Yes, I understand that is copper- crusher. They don't test with the Piezo method for the 257 Roberts? I had a discussion with a gentleman about pressure in the 257 Roberts a while back and he didn't believe Hodgdon's data. He was running it off of a computer simulator program and it was reporting over pressure. I figured they were testing in Piezo and converting it to CUP, but I suppose I was wrong.

Don't know of ANY pressure lab that tests peizo and publishes in CUP. Why would they?

I know of at least two companies that still sometimes test less-popular cartridges with copper-crusher equipment, because there isn't enough demand for the round to justify the cost of a piezo barrel.

Am always astounded at how many handloaders believe computer-simulated data is somehow more accurate than pressure-tested data.

I don't know of any reason for it either. I figured they(Hodgdon) would have given up testing in CUP by now and perhaps converted back to be consistent, and was surprised by new data being published in CUP.

A number of years back I wrote a simple application that converted from CUP to PSI. It was loosely based on relational data and was less reliable in the extremes of pressure data. The thought was they may have a more accurate conversion with all the data they possess.

I didn't make my sense to me why someone would believe a simulation over tested data, but there it was. He was obdurate.

One point I think Steve was making, which appears to be true in my 40 years of handloading, is that the pros in competitive matches, using the same rifle and components, have found that reducing a load does show up not only in less velocity but less primer flattening. I generally agree with that IN THE SAME RIFLE, USING THE SAME COMPONENTS.

Bob
www.bigbores.ca

Bob,

Sure, why wouldn't it?

But that still doesn't mean that relative primer flattening is a reliable means of estimating actual pressure.

Might also mention that I've done a little more primer-appearance testing involving new brass since posting the article. New brass generally has a slight amount of headspace, ecpeacially in factory chambers, though not more than the +/- .007" allowed by SAAMI specs.

First, I noticed that a lot of the brass from once-fired factory ammo had noticeably flattened primers, even though all of it never showed any other sign of excessive pressures, including velocity. This is due to the same reason I mentioned in my post: New brass backing up over a primer that's backed out slightly, then expanded, before the case expands enough to fill the chamber.

Also, with new primed brass, which isn't loaded with powder or bullet, the primer usually backs out a little from the case-head when the empty case is fired. Apparently the "rocket effect" of just the priming compound going off is enough to push the primer backward in the pocket.

Nicely put—good article.

I will attempt to add something useful.

Mule deer mentioned the movement of the primer in the case and while I know that to be true, I've never went about proving it until this morning when I was proving (to myself) that small pistol and small rifle primers are the same dimensionally.

ANYWAYS, I found this large rifle (probably a Federal #210) primer in the catch cup of my Bonanza CoAx. It shows (to me at least) definite movement and "riveting" from the case head (which must be harder brass than the primer cup)



If the image is not clear enough, I can retake the picture with a "real" camera and repost it.

Also: Would not the brass in primer cups, while of the same composition, be "softer" due to less work hardening during manufacture?

RJ

I had (2) consecutive primers blow outta the same box of factory Horn 28N eldx ammo. The double pressure spikes caused the firing pin to blowout the back of its housing and hang the firing pin on the lip edge after it smacked my right thumb.

Hornady asked for the remaining 18 rounds to be sent back for testing to determine if this box got an extra powder dump.

I’m waiting on the results...As someone already mentioned, this can be a common occurrence with factory ammo. 😎

Well, for Pete's sake, of course you had trouble...it's a 700. Can you spell Mauser? Seriously glad you weren't badly injured.

Me too actually....I’ve blown a primer on occasion but (2) in a row, never....I sent the rifle back to the builder for a check up.

They buffed the firing pin but otherwise said its gtg...Mowser for the win. 😬😎

I find John provides info when it is needed. I did need to read this.
I once accidentally used CCI pistol primers while developing loads in a .270- ignition was poor( of course) and the primer strike perforated the primer.
I had purchased 4 and within the taped package , was the no good pistola primers. I seated a few( mistakenly) and then decided to give them a go.
A few ignited the 4350, a few didn't and perforated the primer.
CCI pistol primers were packaged in blue and white slightly different than LR primers.
Anyways, I digress, John keep doing what you do.
Love you stuff

Mule deer???

Huh, too good to answer my questions are we John?

RJ

Didn't realize you were asking a question. It seemed like a statement.

Looking for your input, agree/disagree etc.

RJ

That looks exactly like the "riveting" (or whatever you want to call it) that happens when a primer backs out of the case a little, due to a slight amount of what might be called "extra" headspace--though it really isn't, at least according to SAAMI.

As mentioned in the article, SAAMI headspace specs usually allow for about .007" of variation in chamber/ammo dimensions. At typical modern bolt-action pressures, this often results in "flattening" of primers, due to exactly what you posted: The primer backs out a little before max pressure is reached, with the rear of primer expanding due to not being supported by the primer pocket.

However, the case head is not necessarily "harder" brass than the primer cup, just thicker.

Gotcha, the reason I wanted "to know" was there is some belief that there is a difference in material between pistol and rifle primers and that pistol primers can't withstand the pressures "generated" by rifles. OK, maybe, but small rifle and small pistol primers can be interchanged, but due to dimensional differences large pistol (shorter) and large rifle cannot.

Yes?

RJ

Take cup thickness into account, not just height.

That's what got me thinking . . . Very dangerous . . . So I started measuring heights, thicknesses etc as best I could and with all the Federal and CCI primers I measured, cup thickness between both brand for all types of primers (large and small rifle, large and small pistol including magnums of all four types) cup/wall thicknesses were the same. The only difference being height between large pistol and large rifle.

RJ

Headspace determines primer appearance. The primer always comes out first before being reseated by brass expansion. Look at a straight wall revolver case. Headspace is not at the shoulders since there is none. It is the distance from the case head to the recoil plate. Every single .44 mag can have a dead flat primer well within pressure limits. The force from the flash hole will send a hammer back to near full cock. The squirt from that hole can be horrendous well before peak. To rivet a primer as shown means headspace was excessive by full length sizing too much. It has nothing to do with final pressures.
Fed is supposed to be weaker but I have taken Fed 150 primers to near 60,000 # in the .454 with cut down .460 brass without a flat primer. I tested the 150 to the .500 S&W but the 155 was more accurate and my go to from the .475 up. The 150 is the only for the .44 mag.
Weatherby had ignition problems at the start. Fed was the first to make a mag LR primer that brought the Weatherby to life.

I am far from being any pro, or an engineer for matter. But my observations support this statement.

For several years, based on what I learned reading commonly available literature like my loading manuals, and before the advent of internet message boards, I did a lot of experimenting with several rifles. Most notably a pushfeed Win 670 in 30-06, and also a rebarreled Venezuelan mauser in 30-06 AI, and eventually a Win 70 classic in 264.

My efforts involved brass fire formed in the rifle, resized in FL dies in a manner which only 75% of the neck was sized, and primed with CCI 250 primers.

Then I painstakingly charted charge weight vs velocity graphs for several powders and several bullets over the course of about five years. (note: my experiments exceeded the life expectancy of the 264, and it had to be rebarreled) Some loads were pushed to the point of expanded primer pockets where they would no longer hold a primer after three or four loadings. And I experienced a couple of "pressure excursions" which expanded the case head to the point it would not fit into the RCBS shell holder on my press. "Pressure excursions" being with 140 gr partitions in the 264 loaded over early production RL25. A load which shot under 3100 fps in Nov, scared the hell out of me in July.

Anyway enough background, to observations.

Loss of primer radius definitely correlates to increasing velocity, increasing powder charge, and obviously increasing pressure. The phenomenon is observable and repeatable. I feel it can be used by a very careful observer to indicate increasing pressure values. But every other facet of the load must be held identical.

But the question is, what actual pressure value does the flattened primer represent?
Hell, I have no idea! That is what the chronograph is for.

And how do you define or measure the degree of primer radius loss?

So yes, it is a tool which can be used by the very careful, dedicated, and experienced handloader. But not one to be recommended to the novice as a be all do all safety check.

Now as far as CHE. As Denton told us a decade ago, there is too much noise in the system to get any reliable information. I meticulously measured hundreds of cases before and after firing. The head expansion numbers were so random that they were meaningless.

Steve692


Forgot to take your meds again...…………….


Lefty

MD, I have always enjoyed reading your articles and consider you to be the best common-sense gun writer since JOC.
Your latest article on primers is no exception.
I would like to ask you a few questions. I have been reloading my own ammo for roughly 40 years. I too have found that primers are a very poor method for determining pressure and for all the reasons you stated.
First, I would like to ask you or anyone else here if you have ever seen an example of excessive chamber pressure WITHOUT having a flattened or blown primer? Personally, I have not or at least not ever thought so.
Second, what are the signs that you personally look for to determine if you are at the high or top end of your powder loads?
The reason I am asking this is just this week, I am working up a load for a 270 Win. with a custom barrel. I am using an 8# keg of H-4831SC which I have not used much of. I have worked up to 58 grains of the H-4831SC under 150 grain Nosler partitions with CCI 200 primers along with Lee Collet sized Winchester cases that were fired in the same rifle but with Accurate 4350.
With the H-4831SC, I have already exceeded any book loadings by at least 2 grains and the velocity over my Chrono is still somewhat anemic and far below book velocities.
As of yet, there are no flattened primers. By that I mean the primers are not filling the primer pocket up as is the norm in a high pressure load. There is some primer cup flowing in to the firing pin hole of the bolt face. But there is NO hard bolt lift and the cases extract easily.
For me, bolt lift AND ease of case extraction are the “go-to” indicators for excessive pressure, which is always accompanied by flattened primers at this point.
What are your thoughts on this?

Sorry I haven't responded! Tend to miss the questions on the specific columns, because there usually aren't many after a week or two.

I have had the same experience with recent manufacturing lots of H4831SC, with both a total lack of "pressure signs" and low muzzle velocities. Consequently I've been pushing the published muzzle velocities by 100 fps or so, and usually get better accuracy as well.

But these days there are also other good powders for the .270 with 150-grain bullets, including Alliant Reloder 26, IMR 4955 and 7977, and Ramshot Magnum.

excellent article!
thank you

makes us pause again when someone writes about their particular load, often over those published in manuals, showing "no signs of excess pressure"

/Good article but when I reloaded I used the primer flattening method. For me they only flattened when I was close too, at or above the maximum recommended loads. I liked ball powders because they worked so well in my powder measure but you have to run them at higher pressures or they don't burn clean. The primers started flattening and I'd back down from that until they didn't It seemed to make sense to me. Especially since I never had factory ammo primers flatten.

Just enjoying some pre-Thanksgiving pumpkin pie. Hope all of you are having an equally enjoyable evening.

Two comments:

MD is correct in recalling my test of pressure vs. flatness. A few years ago, I had a fit of ambition and started an article on evaluating pressure by looking at primers. So I loaded a couple of dozen cartridges ranging from mild to maximum, and touched them all off. Then I extracted the primers, marked them, and put them under a bench microscope. I arranged them from roundest to flatest, and found no correlation between powder charge and position in the arrangement. That article never saw the light of day. Bummer.

Again a few years ago Ken Oehler instrumented a pressure barrel with two piezo transducers, each feeding identical electronic channels. He also instrumented the same barrel with two strain gauge channels. Then he fired a series of shots ranging from pea shooter to bazooka. Given that data set, it was not a great task to derive the fundamental precision of both systems, as well as their accuracy. It turns out that each is as good as the other. Neither has a theoretical advantage. Which you use is simply a matter of convenience. The strain gauge system has the advantage of not requiring a hole in your chamber, and the physical quantity conversion chain is a little shorter than that of the piezo system.

Many people get hung up on the notion that they can't very well check the strain gauge against a known standard artifact. That's really not the problem they think it is. We know the rest mass of an electron to great precision, yet no one has ever built a suitable scale and wrestled a single electron into the weighing pan. We know the distances to the stars, but no one has ever laid a ruler along the path to one. There is no standard velocity artifact you can use to calibrate your chronograph. (Rumor has it that NIST did have some at one time, but someone peeked into the containers, and the standards all disappeared into the bush at highly accurate velocity.) There are no standard weight artifacts. What we think of as weight standards are really mass standards. Many of the measurements we confidently deal with on a day to day basis have no directly comparable calibration artifact, and we still get along just fine.

denton,

Always appreciate your observations. Thanks once again!

But would also have to comment that the head of a major powder company's ballistic department disagrees with the strain/piezo results. But that's not unusual in such, uh, sensitive topics.

Might also note that have talked to a couple of long-time heads of major pressure labs. One recommened two specific brands of primers (one SR and one LR) as the most consistent in their tests. The other guy also recommended two specific brands. Neither man's recommendations matched the other--and both had been in their job for decades.

great stuff
thanx

OMG! I'm getting a head ache reading this. I can see the merit in MD's writings. I admit I have been of the opinion that a flat primer meant it was time to back off. But reading this thread is enlightening me. I may be getting ahead of myself here but i'll make this statement. I believe that if you have a real case of high pressure that you will ;probably see a flat primer. But you will see other tell tale signs as well because after reading MDs post I believe that there are at least a couple different things other than pressure that can cause a flattened primer and that if you have a flatten primer and no other signs of high pressure you probably haven't experienced high pressure. The few times I've experienced real high pressure there were several signs of it. One, and the first thing I noticed was a sticky case and hard opening bolt. Another big one that will go along with that is wildly fluctuating velocity and accuracy or just abnormally high velocity. And the biggy, the one that's not readily noticed is an excessively expanded cartridge case base which is determined with the use of a micrometer. Of all the signs I've ever heard of that one is my main one that makes me believe I've experienced excessive, potentially harmful pressure. But I also think that you'll see more than one sign if it's really high pressure. Like I said. correct me if I'm wrong because these are just my opinions.

I would simply say this about excessive pressure. For me, these three happening together give me pause.

1. Felt recoil increases.
2. Chrono display is higher than normal.
3. Primer looks unusual.

Stop.

Don't worry about what was written in this thread. If you follow a manual, and your scale is okay, you are good to go.

article is a joke

About primers. pressures and powders: First, an anecdote about primers in two different .35 Whelens, both single-shots; and then a third .35 Whelen is involved.

The first .35 Whelen was an M7400 (semi). Everything worked well... never a problem, though some handloads were likely over pressure, yet I never used "small base" dies. That 7400 was as tough as any bolt action in ejecting fired cases. Though one load - a book load - did blow a couple of primers. It was a tough, accurate rifle that eventually got sold. A few years later, I went looking for another .35 Whelen and came home with a single-shot NEF. I also bought 50 new Rem cases in .35 Whelen. Loaded up some of the old brass used in the 7400, and some of the new brass, both with WLRM primers. The NEF would not fire the loads with the new brass but would with the old brass used in the 7400. I thought there was a head space problem so took the rifle to my smith who said the chamber checked out. Also, when returned to the place where purchased it would fire Rem factory ammo. I was then stuck with 50 new cases that needed fire-forming. That was my thinking so exchanged the rifle where purchased for one in .45-70. Sometime later, I went looking for another .35 Whelen, couldn't find one so came home with a 9.3 x 62 - no regrets there.

Recently, on an impulse, I purchased a Traditions OUTFITTER G3 single-shot in .35 Whelen with a 22" barrel and brake... It fires those same new Rem .35 Whelen cases primed with the WLRM primers! The apparent real problem with the former NEF was the hammer spring was relatively weak compared to this Traditions that whacks them like a sledge hammer!

Plus... as MD has talked about, there was a slight difference (within specs) for the head-space in favor of the TRADITIONS that has a very tight chamber!

And Steve R., new powders have made a great difference for handloaders of the .35 Whelen... in a positive sense. Plus 200 fps within SAAMI specs for a 250gr. And that's not 2600 fps but 2700 fps from a 24". So technology continues to improve matters over traditional concepts. Check Speer's Manual #14. I've recently been testing the 225gr NAB using CEF223 with excellent results that tradition would have expected from a .338 Win with a 22" barrel.Of course... it too has been "improved" by better propellants.

Bob
www.bigbores.ca

I agree, Bob. Propellant technology continues to evolve.

For me, when these three things occur at the same time, it’s time to double check things.

1. Felt recoil increases.
2. Chrono display is higher than normal.
3. Primer looks unusual.

MD remembers correctly.

I wanted to do an article on flatness vs pressure. So I carefully prepped and fired a batch of ammunition with various powder charges, using primers from the same box. Under a microscope, I arranged them from roundest to flattest. I could see no detectable correlation between flatness and powder charge.