Does a factory load factory ammo to “Factory†pressures, all the time?
Cases in point,
Case Pressure
308 60,000
270 62,300
All the wsm/rum/saum/wssm 65,000
Most weatherby’s 63,000
284 63,800
458 lott 62,800
458 win 62,800
30-06 58,500
30-30 42,000

IMHO, the 308, 30-06, and 30-30 generally “read†primers as being good, but once one goes to FACTORY loads for say, 270, the primers are more flattened than I would like to see.

So, do we think that it is fair to assume that all 270’s are loaded, more or less to 62,300, with an accepted SD for pressure?

Having some experience with one I can say that that one loads to SAAMI specs using pressure barrel data and a sampling plan of the lot of powder to be used. The more uniform the lot of powder is the closer to the SAAMI spec they can load.

What the rest of them do is beyond me.....but it's easy to say that no US factory would knowingly load beyond SAAMI specs.....further they must compete and in that vain I suspect they all load as hot as they can.

I can only guess that every US manufacturer loads the 270 to the same level within a standard deviation or so. The only way to know is to test them all in a pressure barrel....

Based on the anemic velocity of some factory ammo I would have to say it depends. I say "some" because unless you have a chrono it's hard to know. .243 and 7mm mag tend to be really anemic in some loadings.
Then along come the WSM's.....I'd love to see some pressure tests on these with a velocity comparison. I've seen 270 wsm's run just a hair behind my hand loaded 270 wby's and my 270wby has a 26" barrel and is loaded "warm"!!!

DO NOT use the looks of the primer as your "gauge" as to pressure. Factory ammo has some headspace built into it. This in general allows the primer to back out ever so slightly and give a "flat looking appearance"......if you use this as a "thermometer" you will be lead down a wrong path.

quote:

Originally posted by kraky:
DO NOT use the looks of the primer as your "gauge" as to pressure. Factory ammo has some headspace built into it. This in general allows the primer to back out ever so slightly and give a "flat looking appearance"......if you use this as a "thermometer" you will be lead down a wrong path.

Kraky, you pretty much summed up what I was going to say. I don't shoot factory ammo very often but I stopped relying on primer appearance a long time ago.

jeffeoso raises an interesting question about how factories allow for normal pressure variations.

When I handload, I go by the average pressure, and accept the fact that individual rounds will exceed that pressure, due to things like barrel condition, temperature, instrument error, etc..

Seems like a retired Nosler employee posted here about a year ago, words to the effect that Nosler's procedure was to test 10 rounds and reject the load if any one shot exceeded SAAMI pressure, even though the average pressure for the 10 shots might be in spec.

If SAAMI has an official policy on how to account for pressure variation, I am not aware of it. Does a 60,000 psi spec mean the load AVERAGES 60,000 psi, or does it mean the load never, never, ever exceeds 60,000 psi?

Factory ammo will show a flater primer, because the case is loose in the champer and slamed back against the bolt face, compared to a fireformed neck sized only reload.

Just my observation

For some reason, the .243 and 7 Mag are universally way underloaded. It's actually not unusual for 100 gr. .243 factory loads to not top 2700 fps by a lot. The .270 will check out close to right in my experience. From another perspective, why should a .270 go 62300 and the '06 58500?

quote:

Originally posted by jstevens:
From another perspective, why should a .270 go 62300 and the '06 58500?

1896 Winchester lever actions were chambered in both the 30-Govt-1903 and the later 30-Govt-1906 cartridges, prior to the creation of SAMMI in the mid 20's, the 270 was only chambered in bolt actions (the 270 and SAMMI came into existance within 1 year of each other.)

If not the primer, what do you all use to determine high pressure?

Grady, Bolt lift hard, shinney spots on case head, extractor slot imprint on case head is a high pressure sign.

quote:

Originally posted by Grady8541:
If not the primer, what do you all use to determine high pressure?

Welcome to AR....there is a wealth of information to be learned here...put on your hard hat....

quote:

Welcome to AR....there is a wealth of information to be learned here...put on your hard hat....

... and from time to time, your knee boots...

Brianbo, Good retort! But it is special here! Thanks to Saeed and a few other loose cannons.

quote:

If SAAMI has an official policy on how to account for pressure variation, I am not aware of it. Does a 60,000 psi spec mean the load AVERAGES 60,000 psi, or does it mean the load never, never, ever exceeds 60,000 psi?

SAAMI max is just that, the max ALLOWED pressure. That`s at least what I`ve been told. No single round should excede the listed max. This is part of the reason you see a load listed in a manual at 59K when the SAAMI max is 62K The load had a wide extreem spread and some of the loads hit or exceded max.
A-Squares book "Any Shot You Want" has a very good in depth artical on pressures and the variations of differing components from the book loads.

quote:

Originally posted by Grady8541:
If not the primer, what do you all use to determine high pressure?

I use my " Spider sense " , it's about as accurate as most other methods.

And yes , I do mean to stir the pot.

Primers will lead you completely down the wrong path , they all " show " things differently. Softer VS. Harder cups, and why do some guns seem to show a crater on the primer before others when the velocity is the same ?

( if the same load makes the same velocity in a barrel of the same length isn't the pressure most likely very close to the same as well ? )

Most of the other " signs " like case head expansion and pressure ring measurement are only valid if you can compare them to a known pressure to begin with , and the brass is exactly the same. I see a big problem with calibration here , how do you know what pressure you are calibrating your measurements to if you have no data to start with ?

Which brings me back to the " spider sense " thing .
If the primers are blanking ( piercing ) or the case is getting damaged in a single shot you are well above where you need to be, go back now. Right now.
If the primer pockets are still nice and tight after 4 firings ( Modern high pressure rifle only ! ) You can infer that the case head is not expanding .
Also if you are getting higher velocities than maximum pressure tested loads with the same length barrel, you can infer that you are also generating more pressure than that load made when tested. ( only if your components are the same , obviously ).

This is one of those things where some folks seem to think that everything is measurable and knowable , and that any guy who can plug some variables into an equation can figure out exactly what the pressure is. I disagree.

All you really need to know is :
Is it Too much ?
Is it Enough ?
is it not enough ?

You will be guessing .
We ALL guess at pressure.
We are all wrong sometimes.
The whole point is to not blow anything up on accident. (Blowing stuff up on purpose is called destructive testing , and is cool ).

I'm done now , I just had to say it.
Take it as my opinion, or not.


Travis F.

It is a mistake to read case head expansion in terms of so many PSI. It is an
allert that you are pushing the brass into it's yeild range. Very little additional
strength is left at that point. If you load to that point you are betting that all
future brass will be identical, as well as all the other variables.
Some shooters seem to feel that since brass will hold to 80 kpsi or so, they may load to
65 kpsi. When I was young I drove 90 mph on bald tires, now I know better.
Good Luck!

quote:

Originally posted by TBF:

quote:

Originally posted by Grady8541:
If not the primer, what do you all use to determine high pressure?

...Most of the other " signs " like case head expansion and pressure ring measurement are only valid if you can compare them to a known pressure to begin with , and the brass is exactly the same. I see a big problem with calibration here , how do you know what pressure you are calibrating your measurements to if you have no data to start with ?...

Hey Grady, Travis has a slight misunderstanding of how Case Head Expansion(CHE) and Pressure Ring Expansion(PRE) work for those of us that actually use them.

CHE basically measures the "Pressure" required for the Case Head to begin deforming. It doesn't matter what the Pressure is, all that is important is that the Case has Expanded more than it can Contract, making it slightly deformed. Most of us use 0.005"-0.007" as MAX EDIT in: should read 0.0005"-0.0007" MAX allowable CHE. It should be measured on the 2nd-6th firing of the Case - depending on the strength of those Loads.

CHE will not work on some of the older Low Pressure cartridges. The reason for this is because their SAAMI Specs are below what is necessary for the Case to measure a deflection. By the time you would measure it, you would be WAY OVERLOADED.
---

PRE is much easier for people to understand and easier for a Beginner to use. PRE can be used on every Cartridge ever made. You simply take a box of Factory Ammo, fire them and measure the PRE(rotate the Case and record the Widest Diameter of the Pressure Ring), average the results and write that number on that box which is now your Benchmark Standard.

Now you either Full Length Resize(FLR) the Cases or Partial-FLR(P-FLR) those same Cases, do a Creighton Audette Load Development spread of Loads(many refer to it as the Ladder Method), fire the Cartridges and measure the PRE as you go along. When your PRE is the same as the Benchmark Standard from your Factory Ammo, you STOP.

The Factory determines what the SAFE MAX Pressure is for those Cases with their Millions of Dollars of Test Equipment. So, we use their results to establish where the PRE should STOP.
---

Nothing real tricky or complex, just measuring the deflection of the Case at the Pressure Ring. Knowing what the actual Pressure is, is no use at all.

Best of luck to you.

quote:

Originally posted by kraky:
Based on the anemic velocity of some factory ammo I would have to say it depends. I say "some" because unless you have a chrono it's hard to know. .243 and 7mm mag tend to be really anemic in some loadings.
Then along come the WSM's.....I'd love to see some pressure tests on these with a velocity comparison. I've seen 270 wsm's run just a hair behind my hand loaded 270 wby's and my 270wby has a 26" barrel and is loaded "warm"!!!

DO NOT use the looks of the primer as your "gauge" as to pressure. Factory ammo has some headspace built into it. This in general allows the primer to back out ever so slightly and give a "flat looking appearance"......if you use this as a "thermometer" you will be lead down a wrong path.

Agreed. This is pretty much right on the money. Some ammo for relatively modern calibers has been really "wimp-ized" by the factories. An example of this are the low-velocity factory loadings of the 7mm Rem. Mag., some of which are almost down to the 7X57mm Mauser level.

In other cases, they have been known to go the other way. For example, some of the early Winchester loadings of the .264 Win. Mag. actually stretched primer pockets!

Hot Core, where precisely is the pressure ring if one wants to follow the PRE approach? Does that work on a neck-sized only case? I reload both the 416 Rigby and the 404 Jeffery which are both low pressure cartridges. Since I have never shot (can you believe that!) any factory ammunition in either, I will probably have to buy some high priced ammo to find out if my own reloads are within specs.

I think there is another aspect of factory cartridge pressure testing protocols that hasn't been mentioned. Don't they heat up the cartridges before testing them to test for pressure of a cartridge at say 110F ?

quote:

Originally posted by Wink:
Hot Core, where precisely is the pressure ring if one wants to follow the PRE approach?

Hey Wink, It is easy to locate the Pressure Ring on a Fired Case.
1. On a Belted Case, it is the widest diameter forward of the Belt.
2. On a non-Belted Case, it is the widest diameter forward of the Extraction Groove.

You only measure PRE after a cartridge has been fired.

quote:

Does that work on a neck-sized only case?

No, it won't work at all on a Neck Sized case. The reason is because the Pressure Ring is not realigned(resized) with the case wall. It must be either FLRed or P-FLRed so the Pressure Ring is pushed back into alignment, so we can measure the "amount of deflection" when the cartridge is fired.

quote:

I reload both the 416 Rigby and the 404 Jeffery which are both low pressure artridges.

A nice thing about PRE is it will work properly on all Cartridges, even the older Low Pressure ones.

quote:

Since I have never shot (can you believe that!) any factory ammunition in either, I will probably have to buy some high priced ammo to find out if my own reloads are within specs.

I can see where buying Factory Ammo for those large older cartridges would indeed be quite expensive. Just finding them can be a trick.

If it is cost prohobitive to get the Factory Ammo, you can always stick with the tried and true - Lack-of Primer Pocket Expansion. I encourage everyone to use every method available to them. The Method where a person keeps the Load "low enough" that he can get 8-10 reloads on a Case and still have snug Primer Seating, is always an excellent Pressure Indicator.

With your cartridges, you could run the Testing on 3-cases. Load and shoot them 8-10 times. If the Primer Pockets stay snug, you know for sure you are not above where you need to be. Just a bit time consuming, but it works and works extremely well.

quote:

I think there is another aspect of factory cartridge pressure testing protocols that hasn't been mentioned. Don't they heat up the cartridges before testing them to test for pressure of a cartridge at say 110F ?

I don't know, but it does make sense for the Factory to Test at the temperature extremes they would expect their ammo to be used in.

If you have MicroSoft "Word" and "Excel" on your computer, I can send you a document on CHE/PRE and a Load Data Sheet that will help you get started. Just PM me with your email address.

You will need a 0.0001" capable Micrometer because a 0.001" capable Caliper just isn't accurate enough. Or whatever your Metric equivalent of that is. Doesn't matter which Measurement Standard is used as long as it is accurate enough.

It can be a bit time consuming for someone who has never done the measuring before. That is a good thing for me, because it allows the barrel to cool for a bit longer period between shots.

Once a person gets used to doing the measurements and recording them though, it moves along fairly quickly.

Best of luck to you.

quote:

Originally posted by Hot Core:
CHE basically measures the "Pressure" required for the Case Head to begin deforming. Most of us use 0.005"-0.007"

you are off by an order of magnitude..
.0005 to .0007, not .005 or .007...
.007 is the difference between a 257 and a 264 or a 270 and a 7mm.

you certainly bring a wealth of information, but please keep the units correct...

jeffe

quote:

Originally posted by Hot Core:

quote:

Originally posted by TBF:

quote:

Originally posted by Grady8541:
If not the primer, what do you all use to determine high pressure?

...Most of the other " signs " like case head expansion and pressure ring measurement are only valid if you can compare them to a known pressure to begin with , and the brass is exactly the same. I see a big problem with calibration here , how do you know what pressure you are calibrating your measurements to if you have no data to start with ?...

Hey Grady, Travis has a slight misunderstanding of how Case Head Expansion(CHE) and Pressure Ring Expansion(PRE) work for those of us that actually use them.

---

Nothing real tricky or complex, just measuring the deflection of the Case at the Pressure Ring. Knowing what the actual Pressure is, is no use at all.

Best of luck to you.

Hot Core,

It's not that I misunderstand the methods, or think they are absolutely wrong as indicators of pressure in the same way loose primer pockets indicate relative pressure.

What I meant to get at with the above post is that comparisons with an unknown variable are not really accurate. You cannot derive a number measured in PSI from measurement of brass of an unknown hardness.

As you said " Knowing the actual pressure is no use at all " , I kinda think we are on the same page, maybe this is a " what I said isn't what you think you heard kinda thing " ?
Or maybe I'm just not saying it right ?

At the bottom of the post I said :
All you really need to know is :
Is it too much ?
Is it enough ?
Is it too little ?

Which is pretty much the same info you could get from your PRE measurement if you measured accurately. I am NOT saying that YOU personally cannot measure accurately , just that with such small measurements being critical to this method , and having myself used a micrometer a fair amount , it would be really easy for some people to screw this up. Particularly when some of the numbers quoted as being acceptable expansion may be somewhat suspect..........

Comparing identical brass fired in the same chamber , with accurate measurement , and comparing load "A" with load "B" may give pretty accurate results insofar as you just want to know :
Is it too more ?
Is it less ?
IMHO how much more , or how much less, is not really possible to know.

Similar info to the PRE measurement can be gotten by careful examination of the burnishing left after FL sizing a fired case.
I would not assign a number in PSI to this measurement either.

Please don't take my comments personally , or as an attack on the whole concept of measuring stuff indirectly and inferring results. These methods have been used ( and misused ) for many years usually with safe results.

The only measurement I trust is velocity .


Travis F.

I have overloaded many of the 60 different calibers that I handload, and
the primer falls out when the case head sees too much pressure. The
following case heads are all based on the 1892 7mm Mauser design, and
IMHO should all be the same maximum pressure if fired in the same type
of strong rifle. But it is not a perfect world, and the SAAMI registered
max average pressures vary. The 270 does jump out at me as more than the others.

22-250 Rem 65,000 psi
6 mm BR-REM 52,000 cup
243 Winchester 60,000 psi
6mm Rem 65,000 psi
250 Savage 45,000 cup
257 Rob 54,000 psi
257 Roberts+P 58,000 psi
25-06 Rem 63,000 psi
6.5x55 46,000 cup
270 Win 65,000 psi
7mm-08 Rem 61,000 psi
7mm Mauser 51,000 psi
280 Rem 60,000 psi
300 Sav 47,000 psi
308 Win 62,000 psi
30-06 Sprg 60,000 psi [53,200 cup]
8mm Mauser 35,000 psi
358 Win 55,200 cup

Centerfire rifle proof pressures are to be between 1.3 and 1.4 times
maximum average pressure.

Do a proof load in a 270, and the primer will fall out of that brass.

Ralph's Method Of Determining Maximum Operating Presssure:

Warning! This is extremely complicated.

I whip out quickload and get a general idea where I should be. It always works like a charm. I then load sets of three in one grain increments (rifles only). I shoot. I look at the neck.

The neck?

If the soot covers all of the neck and some of the shoulder, I move on to the next hotter batch. I keep increasing the charge until the soot only covers about a third of the neck.

I then stop.

In every case, I have never experienced a pierced primer, hard bolt lift, shiney markings on the case head, or a sticky case using this method. This method works with low pressure rounds like the 30-30 and high pressure rounds like the 30-06. The brass does all the talking.

So am I the only one to try a fired case back in the chamber when near max? I think bolts usually "cam" a case out of the chamber where as to push them back in gives more "feel".

quote:

Originally posted by jeffeosso:

quote:

Originally posted by Hot Core:
CHE basically measures the "Pressure" required for the Case Head to begin deforming. Most of us use 0.005"-0.007"

you are off by an order of magnitude..
.0005 to .0007, not .005 or .007..... please keep the units correct...

jeffe

Hey Jeffe, I certainly appreciate the "error catch" and calling it to everyone's attention. Just went back and Edited in the correct 0.0005"-0.0007" MAX for CHE.

Absolutely the very best feature of this site is having folks with the knowledge to catch typos, especially when it comes to Pressure.

Thank you Jeffe.

Hey Travis, I'm moving this statement up to the top so "we" start off in agreement. Always nice to be able to discuss an issue rather than argue.

quote:

Originally posted by TBF:
Please don't take my comments personally , or as an attack on the whole concept of measuring stuff indirectly and inferring results. These methods have been used ( and misused ) for many years usually with safe results.

quote:

Originally posted by TBF:
It's not that I misunderstand the methods, or think they are absolutely wrong as indicators of pressure in the same way loose primer pockets indicate relative pressure.

Good, we are still in agreement.

quote:

What I meant to get at with the above post is that comparisons with an unknown variable are not really accurate. You cannot derive a number measured in PSI from measurement of brass of an unknown hardness.

Agree.

quote:

As you said " Knowing the actual pressure is no use at all ", I kinda think we are on the same page, maybe this is a " what I said isn't what you think you heard kinda thing " ?
Or maybe I'm just not saying it right ?

Let's just go with " I " misunderstood. Anybody that has done this as long as I have and put down 0.005"-0.007" as MAX for CHE when it should be 0.0005"-0.0007" MAX for CHE occasionally misreads things.

quote:

At the bottom of the post I said :
All you really need to know is :
Is it too much ?
Is it enough ?
Is it too little ?

Which is pretty much the same info you could get from your PRE measurement if you measured accurately.

Yes.

quote:

I am NOT saying that YOU personally cannot measure accurately , just that with such small measurements being critical to this method , and having myself used a micrometer a fair amount , it would be really easy for some people to screw this up. Particularly when some of the numbers quoted as being acceptable expansion may be somewhat suspect...

I agree that if not using a "particular Trick" to reading the PRE, it will be exactly as you mentioned, "really easy for some people to screw this up." I'll come back to this at the end.

quote:

Comparing identical brass fired in the same chamber , with accurate measurement , and comparing load "A" with load "B" may give pretty accurate results insofar as you just want to know :
Is it too more ?
Is it less ?
IMHO how much more , or how much less, is not really possible to know.

We are still in agreement. The only change I'd make would be "will give pretty accurate results". This does confuse some folks who believe they need to know a specific Pressure.

Due to all the Variables in Cartridge Components(cases, primers, powders and bullets) combined with the Manufacturing Tolerances(acceptable variation) in the Chambers and Bores, knowing an exact Pressure would not really be of help. What is a SAFE MAX Load in one rifle, using a specific set of components, has very little bearing on " if " that same Load is SAFE in another rifle chambered for the same cartridge.

quote:

Similar info to the PRE measurement can be gotten by careful examination of the burnishing left after FL sizing a fired case.
I would not assign a number in PSI to this measurement either.

I know the "burnishing" you are talking about, but have never heard of using it as a Visual Pressure Indicator. Perhaps I've misunderstood, or just unaware fo this Method. I'd appreciate it if you would expound on how it works.

quote:

The only measurement I trust is velocity.

Other than getting a "General Idea" of Trajectory, what good is knowing the exact Velocity for you?

Surely we both agree a person can not look at a Velocity and believe it has any relevance to a specific Pressure, because of the Variables mentioned above.
---

quote:

(In reference to measuring PRE from above)...with such small measurements being critical to this method, and having myself used a micrometer a fair amount, it would be really easy for some people to screw this up.

I do agree that it is easy to get this reading WRONG, if a person is not using a specific "Trick", that I've never seen published in a book or Gun Rag.

How about describing the way you would go about measuring PRE and if you do not use the Trick, I'll come back and tell you about it. Then you could try your measurements again and see if they are more repeatable for you.

HotCore,

I think velocity can be pretty valuable as a sign of what pressure may be if the variables are removed as much as possible.

If load "X" makes more velocity in rifle "B" than in rifle "A" ( and both rifles have the same length barrel )I would ASSume rifle "B" is experiencing more pressure to get more velocity.

Likewise , if you get maximum published velocity before you get to the max load , you probably are also getting max pressure .
( again assuming same barrel length )
You could take this a step further and say it would be safe to assume if velocity was lower than the published figure at max charge( in the same length barrel ) you are also not generating as much pressure as the published load.

Again , this only applies to situations where the variables can be removed as much as possible, and still is mostly guessing.
It also only is of any use at all if you have pressure tested data to begin with.
It also only works when using the same components , which pretty much rules out testing that new bullet , or new powder , ETC.

The reference to the burnishing is a pretty crude indicator of pressure , as the case expands and the sizing die scuffs it, you can see the point where the die stops touching the case. As the die diameter is constant , and the case expansion is more pronounced as the brass gets thinner as you move away from the case web , you could infer that if the case is burnished further toward the case head that the pressure has increased.
Like I said, this is somewhat crude as an absolute measurement of pressure , and brass variables make it even more so , wall thickness can vary enough even in the same batch of brass to make fairly inexact , even when the chamber is the same. Using this method to compare different rifles is pretty useless due to chamber dimensions being an unknown variable.

I may not have explained some of what I said in enough detail to make sense , what I am really saying is most of us guess at pressure more than we really know. I hear that even the megabuck equipment used by the pros has a hiccup now and then . Something about variables in barrels and deflection of an exact amount of steel at a given pressure . I also hear that the new electronic stuff is more accurate than ever.

I'd be interested in your " trick " , maybe I have been missing out on something. I have never measured PRE , my comments about measurement of small dimensions come from being a machinist , and seeing all manner of screwups over the years. Measuring .0005 is well within the margin of repeatability error for most of us with a handheld mic.

Again , this is just opinion , and if someone disagrees, that's OK with me !
If you have something to add , or see something wrong with my ASSumptions , feel free to point it out.

Sorry for such a long post.


Travis F.

Hotcore,
didn't mean to me mean about it at all.. I am sure you have heard other folks say 5 thou on this, and sudder!!!
thanks for understanding
j

1) If you are selling ammo for who knows what guns, you need to measure pressure, and bullets must be seated deep.

2) If I am handloading for my own strong rifle, I work up a load until the bolt is sticky or the primper pocket gets loose too fast, and then back off on that load a safety margin.

a) The bullet jammed in the lands, OR if the bullet is seated way deep, it takes less powder before the pressure sign.

b) Of course there are OTHER pressures signs, like case bulge in a semi auto pistol with feed ramp or an AR15 that the brass flows into the extractor and ejector features of the bolt face.



c) For bottle necked rifle cartridge, once you learn the pressure limit for the case, Quickload will predict what bullet, powder, seating depth, and charge will be at the limit. Quickload is typically so accurate that it's velocity prediction will be in the middle of the pack of a string measured with the chrono.

d)Quickload may be wrong and say 1,000,000 psi for a straight walled hot pistol load.
It will not be right for a hot Blue Dot load in .223.

For those that use primer flatness as a pressure indicator this case is an excellent example.

Clearly this case is showing extreme excess pressure...( it's also suggesting serious headspace issues as it's nearly separated above the web)

Yet the primer is not as flattened as one might expect.

quote:

Originally posted by jeffeosso:
Hotcore,
didn't mean to me mean about it at all.. I am sure you have heard other folks say 5 thou on this, and sudder!!!
thanks for understanding
j

Hey Jeffe, I sure didn't take your comments as "mean" at all. Really glad you caught it.

Thanks again.

quote:

Originally posted by TBF:
I think velocity can be pretty valuable as a sign of what pressure may be if the variables are removed as much as possible.

Hey Travis, "How" does a person remove the Variables?

quote:

If load "X" makes more velocity in rifle "B" than in rifle "A" ( and both rifles have the same length barrel )I would ASSume rifle "B" is experiencing more pressure to get more velocity.

Likewise , if you get maximum published velocity before you get to the max load , you probably are also getting max pressure . ( again assuming same barrel length )
You could take this a step further and say it would be safe to assume if velocity was lower than the published figure at max charge( in the same length barrel ) you are also not generating as much pressure as the published load.

Again , this only applies to situations where the variables can be removed as much as possible, and still is mostly guessing.
It also only is of any use at all if you have pressure tested data to begin with.
It also only works when using the same components , which pretty much rules out testing that new bullet , or new powder , ETC.

I don't see the above as a valid argument, simply because it appears to me that none of the Variables have really been addressed.

Obviuosly the "Lots" of cases, primers, powder and bullets are going to be different than those used when the Manuals were written. And even between two rifles from the same Manufacturer, with the same barrel length, there will be "dimensional" differences in the Chambers and Bores along with the difference in the Surface Finish of the Bore.

So, I'm struggling to understand "how" it is possible to "eliminate the Variables". I just don't see it as a possibility, but am willing to learn if anyone can tell me how it is done.
---

It appears to me that most folks with Chronographs just don't realize that using them as a Pressure Indicating device has the potential to mislead them - badly. Velocity DOES NOT equate to a specific Pressure.
---

I appreciate your comments on the Burnishing, but I agree with you that it appears to be, "pretty useless due to chamber dimensions being an unknown variable.", as well as the tolerances of the dies and Cases.

quote:

...I also hear that the new electronic stuff is more accurate than ever.

It may surprise you that I'll agree with you there. The only thing I'd add is, it absolutely positively must be "Calibrated" to the SAAMI Standard. Otherwise, buying a HSGS provides "Unknown Pressure Values" and of course that has a real potential for danger if people just blindly believe whatever reading the HSGS indicates.

quote:

I'd be interested in your " trick " , maybe I have been missing out on something. I have never measured PRE , my comments about measurement of small dimensions come from being a machinist , and seeing all manner of screwups over the years. Measuring .0005 is well within the margin of repeatability error for most of us with a handheld mic.

You will like this, you actually use the Micrometer as an adjustable "Go/No Go" Gauge.

It is totally different than the normal way of using a Micrometer in a Machine Shop, or Quality Lab. You do not "tighten" onto the Pressure Ring to take the reading.

Here is what you do, you take a case and adjust the Micrometer Anvils "close to" the Pressure Ring - without it actually touching. Then you rotate the Pressure Ring between the anvils.

1. If it does not "hang" between the anvils, you tighten the Micrometer just a bit. You must use your own judgment here, and being a Machinest you will pick up on this very quickly.

2. If it does hang, you DO NOT force it to rotate, you STOP and then loosen the Micrometer slightly.

EXAMPLE: Lets say you rotate a Pressure Ring between the anvils and it "will not hang" at 0.3466"(made up number). Then you tighten the micrometer to 0.3465" and the Pressure Ring "hangs" between the anvils as you rotate the case.

Repeat the measurement to verify the reading as you are learning.

Then you record 0.3465" as the PRE on that case and compare it to the Benchmark Standard (which was measured the same way).

If you are under the Standard then you can fire the next increased Load, until what you measure is the same as the Standard and STOP.

Using this Method, all the Variables are "negated", because you are using a Factory Load manufactured to meet the SAAMI Standard to establish your Benchmark Standard.

Therefore if the Bore is "tight" the Factory Ammo will respond accordingly with the PRE Value, but you know it is SAFE to go there with your Reloads at that Pressure Level, regardless of the "Lots" of components.

Measure some PREs, using this Method and let me know what you think.
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People will ask "why" can't you do the same thing with the Chronograph? (Using Factory Ammo to set the Standard.)

You could, but it does NOTHING to indicate what the Pressure was in the Factory Ammo.

You can look in any Hodgdon Manual and see you get vastly different Velocities and Pressures by switching Powders. And since we do not know what Powder is used in the Factory Ammo, we can not just decide it is a specific Powder because the Velocity happens to be "close" to it.

The factories rarely use the same Powders we have access to and create "Blends" to get the proper balance of Pressure/Velocity that they want. The next time they make a run of that Cartridge, they start all over again.

Best of luck to you.

quote:

Originally posted by Ol` Joe:
No single round should excede the listed max. This is part of the reason you see a load listed in a manual at 59K when the SAAMI max is 62K The load had a wide extreem spread and some of the loads hit or exceded max.

Thanks, Ol' Joe. That would indeed explain why so many load book recipes seem to stop short of the maximum pressure. I haven't read the A-square manual. I'd love to spend a few hours visiting with a technician from Hodgdon or Western Powder and learn how they do things.

Hmmm, I don't think the SAAMI limit is actually the max for a single round. The SAAMI pressure standards list all pressure ratings in terms of standard deviations from the mean. I have no clue which shipping box my copy is in, but I'm 90% certain an individual round can exceed the nominal rated pressure. I recall SAAMI being more worried about the probable lot mean than the maximum shot, although there is certainly a spec for the single shot max as well. Without question, lots with bigger spreads will have be loaded down some, but not such that the highest value is under the rated pressure.

quote:

If not the primer, what do you all use to determine high pressure?

Oehler model 43PBL

My understaning is no. From what I have read is they are loaded to the highest average pressure that will not exceed pressure limits when factor in high or low swings. For example, 1 cartridge may have a pressure limit of 65000 psi, but vary by +/- 2000 fps, so the most the factory will load to is 64000 psi. Another cartridge with same max pressure may vary by +/- 3000 psi, so the factory will load for average pressure of 62000 psi. I have no idea what the actual pressure swings are, but this is the gist and have read several times in gun rags are much more prone to pressure swings than others. I believe this is part of the reason some rounds have a reputation of producing velocities more inline with factory published specs than others. Also, comparing pressure tested reloading manual results vs. factory loads, I would say there is some margin in a lot of rounds, not just the traditional rounds underloaded because of old guns.

-Lou

Lou, I stand corrected. I rechecked the A-Square book from which I was trying to recall reading the SAAMI pressure rateing system. The book states the following quotes on pg 139;

quote:

SAAMI specifies a maximum average pressure level for loading commercial ammunition. They also specify a maximum probable lot mean (MPLM), which represents the midpoint of the upper service pressure distribution.

Sounds like one has to keep an eye on two pressure values when working up a load if I read it right.


CIP the European method uses the following which is what I thought I recalled as SAAMI.

quote:

They assign a maximum average pressure for the cartridge. Useing a multiplication factore of 1.15, they then establish a maximum pressure for any individual round in the sample.

This is listed as a single max pressure figure from what I have gathered.

There isn`t any appearent sense to be made of difference in the SAAMI max avg and "MPLM" for a given cartridge.
For example the lists the 25-06 as haveing a max avg of 63,000psi piezo and a "MPLM" of 64,600 psi. The 7mm mag shows 61,000 psi avg and 62,500 MPLM.
The 300 H&H on the other hand has a max avg of 62,409 psi and a MPLM of 71,770 psi! The 9.3x62 is another. 56,604 psi avg max and 65,094 psi MPLM, Go figure!

Hot Core, if I understand your measuring system, it doesn't really matter what the numerical reading on the micrometer is. You are just setting it to a given diameter based on feel as you rotate the cartridge. Once you have set it, you then try other fired cartridges in it. In that case, the numerical reading, and whether it goes to a ten/thousandth or not, is irrelevant. Am I correct?

Hey Wink, Your grasp of the concept is accurate, but you still need the Micrometer to be able to read to 0.0001 (a ten thousandth). Being able to adjust the Micrometer at that level is critical for you to obtain the accuracy level you need.

A 0.001 (thousandth) capable Micrometer or Caliper just isn't accurate enough. Using a tool only capable of 0.001 accuracy will give you the impression it is working properly for this task, but it is not.

You are correct that it can be in either English or Metric, the scale doesn't matter.

There is a mail order company here in the USA called Widener's that offers 0.0001" capable Micrometers for about $20. They will do fine for measuring PRE on any case. And if we have them that inexpensive here, there should be somewhere close to you that you can get a similar price. Widener's may do International orders, I don't know.

But that is just one place. Midway, Graf's, and all the Reloading Supply shops carry some kind of 0.0001" capable Micrometers.

I got a 0.0001" capable Micrometer with the "Thin Blades"(anvils) at a Pawn Shop for $25 that work just fine. At that time, they retailed for $165.

If you don't have a Micrometer capable of 0.0001 accuracy, then forget measuring PRE. Stick with firing 3-5 cases with the same Load 8-10 times to make sure you still have snug Primer Pockets.

Best of luck to you.

quote:

Originally posted by Ol` Joe:
SAAMI specifies a maximum average pressure level for loading commercial ammunition. They also specify a maximum probable lot mean (MPLM), which represents the midpoint of the upper service pressure distribution.

Thanks for the info, Ol' Joe.

I interpret the "midpoint of the upper service pressure distribution" to refer to a particular point on the bell curve for that particular load, in other words, it would be a function of the standard deviation. If I remember correctly, one standard deviation covers something like 67% of the distribution curve so the midpoint of the the curve would be less than one standard deviation. I don't have a reference book handy at the moment so I can't tell you the exact number, except that it is probably less than one standard deviation.

Which brings us back to different loads having different standard deviations which would explain why some load book data stops well short of the SAAMI max.

I wish they would just spell it out mathematically, like the CIP spec, instead of talking in jargon.

I'd love to talk about pressure measurement all day long but I don't want to hijack jeffeosso's thread. Suffice it to say that I think that all forms of pressure measurement, even the state of the art factory labs, are not as reliable and accurate as commonly believed. There's just too many variables, and no absolute way to calibrate (comparing to SAAMI ammo is a "relative" and indirect form of calibration, not absolute and direct, and it raises the question of how does SAAMI calibrate their ammo and how trustworthy is the SAAMI ammo ?)

Getting back to the original question, my take is that the 3800 psi difference between a 270 and 30-06 is almost academic, when you allow for calibration error and shot-to-shot variations.