Home Forums Hunting & Shooting Ask The Gunwriters Pressure signs.

How much over pressure does a cartridge need to be to show pressure signs? Now that I've got quick load I'm questioning a lot of my loads.

As a very rough rule of thumb, pressure signs start around 70 KPSI and primers fall out around 80 KPSI.

If you wake up behind the bench with a scope stuck in your forehead, chances are you should drop down at least a grain or two.

Once I started actually conducting pressure testing, I began to question my "youthful load development".

One day we pressure tested some proof loads that were ~80,000 PSI.

Visual observation of case #1 would make most handloaders say "Think we are just about maxed out. Might stop there"

Visual observation of case #2 would make most handloaders say "Wow, we are getting great velocity but not much pressure sign. Let's go up another few tenths and see what happens".

I went home and pulled some handloaded cartridges that evening.

I watch velocity closely now (don't have pressure test equipment any more). If the velocity is high, I know the pressure is high.

Agree.

Here's an example of primers falling out over 80K.

I've posted this before. I'll post it again as a reminder that even a "careful" reloader can make a mistake.

https://www.24hourcampfire.com/ubbth.../Number/9781434/Searchpage/9/Main/680006

DF

Chronograph.

Chronograph.

Chronograph.





Dave

mog75,

One of the classic examples of what Denton posted is the 7mm STW. When it was a wildcat, most fans reported 140-grain bullets getting 3600-3700 at safe pressures and 160's at 3400+. Safe pressures meant no "pressure signs."

When Remington started pressure-testing the more popular handloads the vast majority were between 70,000 and 75,000 PSI. Which is why Remington's 140-grain factory loads stopped at 3400 fps.

The strength of the brass affects the safety of loads as well. I've had book starting loads of Varget loosen primers on Federal .308 brass. The loads were pulled & double checked, and the charges & powder were correct. I've also seen Federal 7mm-08 brass that was a little soft, and .38-55 Starline brass that started to loosen primers before they should have. In situations like that, I look for stronger brass, if available.

In general, if I have a rifle that is very strong compared to the brass, I will watch both the chrono and the case heads. Short brass life implies the load is too hot, regardless of action strength.

Excessive headspace can also cause flat primers, even if the load is not excessive.

If the action is old or a less strong design, then I'm going to watch the chrono and use book loads, to avoid stressing the action.

Fooling around with a .300 RUM, I've run some loads that were quite fast & pretty accurate, with good case life in strong Nosler brass, but in the end I backed down some and found even better accuracy.

measuring case head expansion on virgin brass ?

I have found the chrono to be invaluable, if the speed is really great.. Perhaps I should look a bit further. To me an absolute indication is a flattened primer, ejector marks on the base (depending on the action) and a sticky bolt lift.

Quick load so far has been extremely close on the velocities(never more than 50 fps off), but the pressures are sometimes extremely high. Can I assume that when it's nailing the velocities, that it is also pretty close on pressure?

ldholton,

Measuring CHE doesn't work UNLESS you have a pressure-tested load to compare it to, using exactly the same brass. I've run several experiments on this in a commercial piezo-electronic lab, and brass varies so much in thickness and the exact composition that anybody who claims X amount of expansion means Y PSI doesn't know what they're talking about, much less whether the load is "safe."

A chronograph is a far better indicator than CHE.

That's kind of what I was thinking. no real control suspect to start from

Thank you all very much.

If you shoot a lot you can detect over-pressure by recoil alone.

To be clear, my point about checking CHE is that if the solid web of the case is expanding, the load is too hot. Not talking about the pressure ring, ahead of the web, which does expand and get resized by a FL sizer die. The cause might be one of several things; it could be soft brass. I use it more as a double check, while also looking at the chrono results.

I too was referring to that. Always read that .0001 was or .0002 was max and .0003 was hot. but wondered about how to tell how much certain brass would expand at a known pressure.

It would have to depend on the brass, not only its yield strength, but also the case design.

Impressive - a calibrated shoulder!!

Regarding head expansion or pressure ring expansion measurements...would the following method have a decent degree of accuracy?

Fire several rounds of factory ammunition and measure.

From the same box of ammo, pull bullets, dump powder, and remove primers from several rounds.

Replace primers with what you want to use; do the same with powder and bullets.

Fire several rounds, record measurements and compare with initial measurements of factory ammo. Of course, chronograph everything.

This is assuming that the brass in one box is all from the same batch and has identical metallurgy. Is that a reasonable assumption?

Here is some actual data from a Finnish Mosin instrumented with a strain gauge. The standard deviation of the random error in that particular system has been measured at 335 PSI, which is practically the same as a good piezoelectric system. The case head measurements were made with a Mitotoyu blade micrometer, clamped to a granite inspection block to ensure that all measurements were made at the same height on the case head. Since cartridge cases are not perfectly round, three measurements were made on each case at different orientations, and the three measurements were averaged.

The brass was all from the same batch, having been fired once.

Note that there are two rounds that were over 60 KPSI that measured .0001" or less of case head expansion. If you follow the 95% PI intervals across the chart, .0003" represents something between 49 KPSI and 75 KPSI. Close enough for you?

The R-Sq value shows that 23.5% of the change in case head expansion is attributable to pressure, and the remaining 76.5% is attributable to random error. If you like a measurement system that is 3/4 random error, then CHE is for you.

No matter what you do, case head expansion is NOT a reliable pressure indicator. If it were, that's what industry would use.

You will not look better with a rifle bolt where your nose once was.

Depends on the primer too.

Winchester will show signs before CCI.

and seems some win. primers will leak aT Mexican food fart pressure

I've seen those reach 80,000 psi pretty easily.

Best pressure sign I know of is having to beat the bolt open with a rubber mallet.

That, and the self-depriming case . . .

It still amazes me that there are folks who think CHE is a valid method.

I don't know anyone that has actually conducted Piezo pressure testing and considers "Traditional Reloader Signs" as valid pressure indicators for load development.

Piezo is certainly not perfect...but it is better than most anything else we have.

Strain Gage is a pretty good method of measurement. Same comment applies.

Beyond published velocities would be a fair indicator as well.

So out of curiosity, did anyone section the cases, and run some microhardness measurements on the brass, to determine the hardness range in the case webs? It would also be worthwhile to measure the internal dimensions of the brass, to see if is consistent. You mention it's a Mosin, so 7.62x54R. I never have worked with one, but I would wonder how consistent the brass is made for them - quality or plinking grade.

Measurement error is a fickle witch, and I've run into it many times over the years in manufacturing. The one I always remember is some stampings that we heat treated, which had to be tested at a GM-approved lab for hardness, to be approved as first articles. The lab significantly disagreed with our testing. After a week of head scratching and phone calls, I sent the same specimen to a different GM approved lab. They agreed perfectly with us. So I submitted the first articles with their test report

I agree, you can't say .0002" expansion is 50ksi, .0004" is 60ksi, etc. Too many variables are in play. But I'm still going to measure case heads, because if they're expanding too much, there's a problem, regardless of what the chrono or other instrument is telling you.

What is "too much" expansion?

In a strong modern action, bolt or falling block single shot, more than .0005" would be a red flag to me. Especially if the chrono likewise shows higher velocity than expected.

In older guns, or weaker style actions, follow the book & the chrono.

Book velocity or max charge, whichever comes first, at least for me.

tex n cal,

And how did you arrive at .0005" as the magic number?

Chronograph and common sense are my guidelines.

Too good is too good. Puzzling is puzzling.

I've blown up a few. The chrono doesn't lie.



Travis

It suggests to me that primer pockets are going to be loose in 2-3 firings, which is too soon.

The diameter of a primer pocket grows about 2X as fast as the OD of the case head.

<shrug> it's a "red flag" for me - meaning stop & evaluate what's going on. Bear in mind in the past 5 years I've seen 3 instances where reasonable loads produced excessive case expansion, without any other indicators of high pressure, so that's one reason I'll stick to CHE.

I look at a variety of factors to judge what to do with a load - speed, accuracy, case life. If all three are good, and the bullet is appropriate for the task at hand the load is a keeper.

The thing is with case head expansion (and I do use it from time to time), it will not tell you what your pressure is but if there is measurable expansion, you can be fairly certain it is too hot. I must also mention; a lack of expansion does not necessarily mean a load is safe. Rocky Gibbs was a believer that the brass was the weak link and looked for the hardest brass he could find so he could load hotter. His feeling was, if case life is good, the load is safe. Unfortunately, a lot of his customers skipped over the brass recommendations and blew the primers right out of their commercial Remington brass.
Speer used case head expansion in developing some loads in their early manuals and some of those loads are HOT.
If a rifle chamber is cut so that it allows no expansion, it will obviously have an effect, This is especially true with rimmed cartridges where most of the cartridge is contained in the chamber. GD

Yea,

I used to shoot some load out of an old Speer manual......until I figured out they were waaaaayyyyyy too hot.....

Different brands in various cartridges may react differently. For example, Remington nickel-plated brass used in a Ruger No.1 in .45-70 would handle 60,000 to 63,000 psi (as measured by a US lab) for at least 10 firings with no discernible primer pocket expansion (using WLRM primers). They were then thrown out. Federal nickel-plated .45-70 brass couldn't begin to handle that psi before primer pockets were loose enough to not hold new primers.

The report from the head ballistician to me was, "You have just reinvented the .458 Winchester Magnum, what was the recoil like?" From a 24" test barrel their average MV was 2096 fps from the 500gr Hornady Int. RN. A rep from Ruger told me, "The Ruger No.1 in .45-70 is just as strong as a Ruger No.1 in .458 Winchester Magnum.

The word from that well known ballistician was "That load is safe in your Ruger No.1". No one in that lab had any previous idea that using the right powder, primer, case and bullet, that a .45-70 case could safely be used at those specs in a rifle capable of easily digesting it. I was getting an average of 2015 fps. My "new" Ruger in .45-70 had the throat lengthened nearly twenty years ago for even better performance by seating bullets "long".

There are opinions, and then there are facts.

Bob
www.bigbores.ca

My thought process is, once the gun is in hand and the target game decided, I ask myself what is the limiting factor on this setup. Is it the rifle, or is it the brass? If it's a strong modern bolt action or single shot, then the brass is the concern, and monitor the brass most closely for long life. The chrono and reference books are useful tools, but again, I've seen brass fail in cases where the book and the chrono said it was a good load. You also have to consider the bullet. You could safely launch a .30-30 bullet out of a .300 RUM 1000 fps faster than its design velocity, but obviously, it's not going to perform properly.

Perhaps someday I'll obtain a pressure measuring gizmo, to add to the toolbox. If the action is old or of lesser strength, then the brass may not the limiting factor in load development.

To me the craft of handloading is one of making high quality ammo, that accurately launches projectiles appropriate to the task. The ammo should safely utilize the full potential of the gun, while still keeping an appropriate safety margin. To those ends I'm going to use judgement, and a variety of tools.

This explains why the primer pocket grows faster than the OD of the brass. It does not matter how hard the brass is.

The same thing is true of the chamber of a firearm, except that we take care to keep the steel within its elastic limit. The inside of your chamber experiences higher strain and expands more than the outside of the chamber. The thicker your barrel, the greater the inside strain.

Yours is the goodest answer! Well said! But people won't believe you. Most want an overly technical answer that they don't really need or understand. Perhaps you could re-word it so it sounds, you know, erudite and overwhelming.

P.S. I did have a Shooting Chrony once that liked to embellish the truth.

I used a Shooting Chrony for quite a while, but got way too many Err messages and sometimes obviously bad velocities. I took MDs advice and got a Pro Chrono a couple years, ago and it is much more consistent and reliable. I know still a cheap chrony but it's working for me.

CZ550:

I suspect it took a man's man to handle those 45-70 loads. Have my Marlin jacked up to 1750 fps with 400 grainers, and it's not fun. That will be revised with their next loading.

Ringman, is that you?

You'll have to provide a finite element analysis to support this. (jk)

That would be great fun! So far, I still lack the software.

I've been following this thread w/o comment till now.

What I'm 'fixin' to say illustrates my progress as a handloader SINCE joining the 'fire'.

"The best 'pressure sign' is NO pressure sign!" ( you may quote me ifn you're amind to)

Research average velocity for cartridge/bullet/bll length - chrono till you get there.

There are no good replacements parts for eyes, nose, fingers, etc.


Jerry

There is absolutely nothing about an extra 75 fps that makes a 'maybe' sticky load worthwhile for hunting. Standing around admiring the shot with an empty case in the chamber has never proven to be an effective method of ensuring great outcomes. Sticky cases might not cause one to stand around, but the effect is just as 'worthwhile'.

There isn't a hunting situation where I'd take 100 fps more given other issues. Its really just not needed.

I do have to learn how to cycle that bolt though for the future.....just not a thing that I do down here.. but I know I have to learn to change... won't take much though.

Let's throw this question out there. Ok you get your manuals out, find a top end but reasonable target velocity. set up chrono. and go to work only to discover your falling like 2-300fps short of listed velocity with listed max charge. With same powder, cases primer , bullets ,COAL ect. so you start going over book max. charge 1,2 ,3 grs. when do you accept you have a slow rifle or maybe ultra smooth (slick) barrel or other reason to not build the pressure to reach target velocity to where you need more powder to reach pressure ?

When you get "pressure signs" ! !






Seriously I don't have a definitive answer to your ? That's a problem I've never encountered BUT I know that others have.

Mr. Denton ? Mr. Mule Deer ? et.al.


Jerry

KINDA OF MAKES ONE SAY UM , For me the annoying one is 70gr 243 NBT Nopsler list a bit over 3600fps I,ve alwys gotten they accurate load to shoot well, but never much over 3400fps this has been in several rifles, even taking in to account barrel length deducts.

I have never had a firearm that gave velocities far slower or faster than expected, so I've never been able to experimentally test the question.

I've seen a Sierra tech rep express that you can add powder until you reach rated MV.

That's probably dangerous because with some loads, MV reaches a point where it does not increase with more powder. That happened to me with a 308 and 2520 powder.

jwall,

Faster or slower velocities than expected are common in rifles chambered for some old military cartridges, especially European rounds, because throat length varies considerably. The original military throat lengths for the 6.5x55 and 7x57, for instance, were designed around very long round-nosed bullets, while some (but not all) modern sporters have much shorter throats. The 8x57 can also vary: While the original chamber had a very long throat for the typical heavy roundnoses, it was eventually shortened for the later light spitzer load--but some later civilian sporters also had longer throats, because in the early days of soft-nose cup-and-cores many hunters preferred long, heavy bullets for their superior penetration. I have just such a German sporter with all the usual touches such as double-set triggers, slim stock with side-panels and Schnabel forend, etc, and its throat is long enough to swallow 250-grain Woodleighs Weldcores with no trouble.

But even modern rifles can have slightly varying throats, or bore dimension. I've handloaded for more than a dozen .270 Winchesters, and the same loads would produce anywhere from 2900 to 3100 fps with 130-grain bullets and various appropriate powders such as IMR4350 and RL-22. If I ran into a slightly "slow" barrel that wouldn't get 3000+ fps with a 130, I added more powder to get there, and never have run into apparent pressure problems--even in a couple of rifles with 20-21" barrels. However, have also loaded for a couple of .270's that got 3100 fps with listed data, and since I didn't see the need to go for more, I quit there--unlike some handloaders who think any load that's apparently "safe" during one test will always be safe in all conditions.

One of the reasons I use a chronograph when working up loads is that, like Denton and the Sierra tech, I've also been told by more than one pressure-lab tech that adding a little powder to loads that produce lower velocities in a given rifle is a safe, as long as velocity was within "normal" boundaries.

That's kind of what I've always done when velocity quit going up with increased powder charges or went up very a little. I started going back down until the velocity starts dropping back off and call it done

The 338 Win Mag is another one which seems to get leaned on pretty hard sometimes, a deal which makes little sense to me considering the applications it often gets applied to...where reliability is paramount.

Id -

I had a 'different' situation that involved 'noticeably' less velocity (-200 fps) than I HAD BEEN getting. I am going to drastically reduce this story to get to THE answer.

This was @ 1990. I was shooting a 270--130 gr.--with a load that was KNOWN for an honest 3100 fps. I was shooting the same components - maybe a different lot # - BUT some new cases from a reputable maker. I had the loads ready so when I went to chronograph some other stuff, I thot I'll just check those loads out of 'curiosity'.

CURIOUSLY what had been going 3100 was ONLY 2900 ! ! Shaking my head, scratching my head ? ? ? LONG story short. I double checked the powder---and---primers separately. This took a couple of weeks of loading and graphing. Then, as a last resort) I RE-USED those same components in OTHER brass.

The load was compressed so there was NO adding powder to the charge.

Bottom line - the NEW brand of brass cases was THE culprit. Yes! !- I lost 200 fps in those cases ALONE.


I have since used that BRAND of brass with NO problems. There was some lot/lot variation or problem. For a few years I refused to buy that brand but 'eventually' I tried some others and they work fine.

I know this doesn't answer your ? but it shows queer stuff does happen.

Jerry

Queer stuff w/ a .270? Goes without saying . . .

As queer as You ?




Just asking.

Jerry

Loads that behave properly in new brass can be over the edge the next go around in the once fired brass. Once again, the chrono will tell the story as the load is faster in the once fired brass.

Why would the same load be faster in once-fired brass vs new brass?

Many times a load does chronograph slightly faster in fired brass than in new brass, but it has nothing to do with higher pressure. Instead a little bit more of the energy from the powder is used in "blowing out" the new brass to fit the chamber, rather than pushing the bullet. This effect is slightly larger in fire-forming improved cartridge with new brass.

Fired brass might result in slightly higher peak pressures due to working-hardening the neck, whether through firing or resizing, resulting in the neck not releasing the bullet as easily. We know that "cold welding" of a bullet in the neck can result in higher pressures.

Or at least those are the conclusions of some shooters, including at least one pressure-lab tech I know.

My 243 win with 90gr Scenar in lapua brass, chronos 30-50 fps slower on first firing. After the first firing the cases are resized with Redding body die and necks are sized with Lee collet die. The velocities are measured with a Labradar.