I'm doing some loads for my new .270 WSM and have a few questions. My first trip to the range with 10 rounds only left me with 3 rounds after sighting in my scope on my new Savage 116 BSS. That first 3 shot group measured .86" MOA including a called pulled 3rd shot> The gun has a lot of accuracy potential from what I can see. What surprised me was the amount of recoil! Keep in mind that I shoot a .338 Win and a .300 Ultra. That first shot was an eye opener! What I need to know is how do you measure(or where) case head expansion, and what is an acceptable amount of expansion? In arbout 30 years of reloading, I've never worried about this, but I'm still almost 4.5 gr below max, and my primers look pretty flat. I'm using 70gr of Magpro with a Federal 210 primer and a Nosler 140gr Accubond. Two of the 3 shots were almost in the same hole, and I knew the minute I pulled the trigger that I pulled the shot. Still got a sub MOA group. Next range trip I'll take the chrono to see what velocity I'm getting, but this load should still have some headroom. Back to the measurement:where do I measure and how many thousandths of expansion are ok?? Thanks.

bowhuntr

Case head expansion no matter how little or how much is a reliable method of pressure estimation....way too many variables.

If one goes by all the different ways to estimate pressure then nothing short of sending the gun and loaded ammo to a manufacturer or Whites lab is qualifing...

Case head expansion is probably the most accurate home estimate, along with primer cratering, flattening, primer leaks, sticky bolts, use of chronographs, all these things are indications and the fact is they have been working for years and years...regardless of the BS on the internet..and they are recommended by the loading companies in there loading books, but the local experts have blown all the theorys...

I have never blownup a rifle in 60 years of handloading and only twice stuck a bolt and perhaps blown 3 or perhaps 4 primers at best....I used the old standard methods for the most part.

Now I have not complaint with all the served knowledge, it is usefull and I listen to some of it, some I take with a grain of salt, some I totally ignore, but I, like most, don't have the technical equipment to deal with all this stuff, so I work up my loads until I see a problem start then cut 2 grs. and call it good, so far it has worked..

I would prefer 0 head expansion, and that will cost you about a grain or two of powder and very little velocity however .005 is acceptable expansion and .015 is max according to the book I am looking at right now, but I would not accept anything over .005 myself, and of course this by itself may or may not be a good reference but combine it with the other above methods and you'll alway be OK IMO>...

Expansion from factory unfired to factory fired? Expansion from factory unfired to fired reload? Expansion from unfired reload to fired reload? None of those mean squat as far as pressure goes, as they only indicate how sloppy the chamber is relitive to the unfired brass.
Differance between fired factory and fired reload is what you need to look at, as long as you remember that the resalution of the measuring equipment is the limiting factor. There you wouldn't want to see more than a .0002 (if that much, depending on the SAMMI pressure spec for the cartridge. A factory 7mmMauser I'd accept at that level, but a 63KSI cartridge I wouldn't accept anything more than factory level expansion). Consider that a caliper is only good to .002, a standard micrometer to .001 (.0005 in the hands of a experanced machinest), and a "tenth's" micrometer to .0001 (and the brass will expand that much due to the heat from your hand holding it).

I agree with Tailgunner, only a few tenths should be there. However, it is dependent on the chamber. I had a Swift Savage rifle that shot very well, but had a big chamber. It would show case head expansion every time, AND flat primers when I knew the load wasn't hot. I started neck sizing only, so the case fit better, and no more flat primers, they acted as they should have. In a good chamber, a couple tenths is a good indicator of pressure, along with stiff bolt lift.

I've been doing a lot of reading on this the past few days. One of the big variables is where you measure the web area of the case. It seems that on the first firing, we are talking about SAAMI spec to actual chamber, so the possibility is there of some excessive expansion. In my case, I measure .007 from unfired to fired. This load is 4.5 gr below the max. From what I can see, this measurement is probably meaningless or at best, something to use for future comparison. In 30+ years of reloading, I've never blown a primer and only once had a stiff bolt lift. I have had some pretty flat primers though! If you believe all that you read, even flat primers are meaningless due to headspace variations. I mostly neck size after initial firing. If I know I'm going on a hunt, I use new brass so I don't have to deal with chambering issues at a critical moment. There's been a lot of discussion here lately about pressur, a lot of it over the head of us "non-physicists". I'm just trying to make some sense of it all.My loads, by the way are new brass to new reload.

bowhuntr

bowhuntrrl,

When I bought my 7WSM, there was not much reloading data or info about it. I used the method you're talking about (Ken Waters "Pet Loads") to try and see where I stood with my loads. I measure about a half inch, give or take, above the base and once you get a feel for it, it seems to be a reliable gauge of pressure for my guns's chamber.

My new 7WSM Winchester cases are the same size as yours, I believe, on the main case body besides the shoulder and neck. My new WW brass measures .550" when new and are actually undersized as my Redding three die set only F/L sizes them back down to .554". I can get as many as two or three firings with my new brass (depending on how hot the load is) by neck-sizing only before the pressure ring expands to over .554 1/2". Then I F/L size it and if I use close to max loads, about every time after that. The way Ken Waters did it was to fire a factory load and compare the before and after micrometer readings.

The Redding three die set I have includes a neck sizing die and I don't have to trim my cases very much at all because of the sharp shoulder not letting the brass flow as much. Hope you can understand my post as I'm not much of a writer and hope this helps some. BM

Bill

ALL previous posts make sense ..sounds like you are working with a hunting piece .. I have been working up a load for the 7mm WSM .. bullet goes in right where the cross hairs cover.. you still have to hold on .. REMEMBER, Precision beats power every time ... work up the load for consistant, smallest group ..(which might be well below max ..anything under 1" off the bench is great).. sight the cannon in, and go kill the beast.. dead is dead .. 100 fps and max chamber pressures will never make the difference if you can't hit'em ..misses are usually a problem with the space between the ears, and the connection to the finger .. I've never had a gun that didn't shoot better than I could hold it .. mb

Seems like we got two different things being discussed. Case head expansion and expansion at the web. I measure web expansion, like Waters. The case web is tapered thickness brass. The chamber is tapered from head to shoulder. Higher pressure will cause the case web to expand further toward the head than lower pressure. Therefore you will see a greater diameter at the web with higher pressure than with lower pressure. Since the outside of the brass is tapered it happens in systematic way.

You can also polish the case with steel wool before firing. The part that expanded into the chamber walls will reflect light differently. You can line up your fired cases low charge to high and see the expansion moving toward the case head.

Here is what I do. Fire some factory ammo and get a baseline. I then pull the bullets from factory ammo and use my compontents in those cases. Using incrimentally larger powder charges. You can measure when you reach factory equivelent pressure with a micrometer. I always use the largest measurement of several taken radially. The cases won't be perfectly round. If you use cases that are harder, softer, thicker or thinner, the results won't be as reliable. I do feel confident enough that I will use that relative pressure data in other cases of the same brand. So, if I find that 50 gr. gives me factory expansion, I feel confident that I have a safe load. I also find that duplicating factory pressure is in the ballpark for an accurate load.

Case head expansion, expansion of the solid web, is a whole other thing. You are making the brass flow. I have not messed with case head expansion measurements.

NO amount of "case head expansion" is acceptable!! The case head SHOULD never yield with any of your handloads!

Now the pressure ring area of the case, which is ~ 0.25" -0.3" forward of the base of the cartridge will expand. The allowable amount is a function of your rifle. As had been stated it is NOT a very accurate method and should only be used for "A" to "B" comparisons and even there I have no faith in it.

ASS_CLOWN

Once upon a time, there arose a considerable discussion on this board about whether CHE and PRE work. One faction said they are fine. Others had doubts, and still others roundly criticized CHE and PRE.



Without much forethought, I volunteered to run an experiment to see if they work or not.



Unfortunately, the result is that neither system is very reliable. PRE is the better of the two, and it has just enough resolution to fairly reliably distinguish between a 44,000 PSI load and a 73,000 PSI load. This confirms work done by Ken Howell, and others, that indicate that the methods are unreliable.



Since you will probably never blow up a gun, short of some outrageous load, the illusion is that the method works. You measure your expansion, you stop increasing your load, and it looks like the method has worked, because you have no indication of failure. For some shooters, the beauty of this arrangement is that they get to shoot 70,000 PSI loads that are 200 fps over book, and still think it is OK. [Well, maybe it is. We don't actually know if SAAMI specs are correct, but I'm willing to make that assumption.]



Test Method: Several matched pairs of cartridges were loaded, with expected pressures spanning a 30,000 PSI range. Each case was measured, using a Mitutoyo electronic micrometer, with resolution to .00005". If PRE or CHE were self-consistent, the same pressure should produce about the same expansion. If they produced exactly the same expansion, the Interclass Correlation Coefficient would be 1.0, which is ideal. Measurement systems with an ICC of .9 or better are considered adequate, and those below .7 are considered unacceptable.



PRE produced an ICC of .39. CHE was worse. By comparision, published piezoelectric pressure data would produce an ICC of about .95 or so.



Putting it in more concrete terms, of the 30 or so cases measured, six were in the 60-65,000 PSI range. The largest case head expansion of these was .0004", and the smallest was 0. So about 62,500 PSI corresponds to something between 0 and .0004" CHE, in that cartridge, with that lot of brass.



Long and short, you may check a couple of cases, and see no growth, and think you're fine, and be way over the limit.



The amount of statistical noise introduced by variation in the brass is so great that you have to average an impractical number of cases to get a repeatable number.



I wish I had a more encouraging report, but that's how the data came out.

Denton,

If the actual case head is expanding, which is should not, then you are either:
1.) over-loading the case
2.) use some soft brass

In either case repeated useage may if the over-load is relatively small, work harden the brass, therefore potentially increasing it's strength and ending further deformation, or you will ultimatley blow a primer.

I agree wholeheartedly as to the VAST error in the PRE system. I think that CHE is more accurate but only when taken to ultimate case failure, read leaking primers, and then backing off the load by 10% or more! This is a dangerous method though as you are testing the ruptured case gas management system of your firearm. On many firearms there is not such system and the gas WILL TAKE OUT AT LEAST ONE EYE!!! Not a happy situation, in my book.

ASS_CLOWN

So, since I have two eyes, I can check up to two loads...

Hey bowhuntrrl, Both Case Head Expansion(CHE) and Pressure Ring Expansion(PRE) have been in use by "knowledgeable" Reloaders for well over 100 years. Two of the absolute best Reloading gurus alive today, Bob Hagel and Ken Waters, have written "positively" about both methods for years.



In fact, the last copy of "Handloader" I got with a Ken Waters Report in it, has him using the methods just as always. I do find it interesting that a man with his resources (both monetary and any kind of technical support from the magazine he would ask for) has chosen to totally ignore the "Home SGSs" all these years. Obviously he has chosen not to endorse "Fools Gold".



So, if you decide to use CHE and PRE, you join a vast group of knowledgeable Reloaders who do likewise. And yes indeed, some measurable CHE is perfectly acceptable. Look in any of the Speer Manuals for verification of that statement. No, you will not "blow up" a firearm if you use CHE and PRE properly.



You can get the information on how to perform both TOTALLY SAFE methods in lots of places. And there are a few specific things you can do to enhance the accuracy of both methods. I have a rather extensive, very detailed File concerning the methods I would be glad to email to you, or any of the Reloaders who may be having second guesses about how well they work. Just make sure your email address is accurate in your Profile and tell me you would like a copy.



Great, time proven, cost effective methods which actually allow you to have full confidence in your Loads. Much, much better than having your billfold destroyed for a totally worthless "Home SGS" where you have to "guess" at the Set-Up and can't Calibrate it - Fools Gold!

Hot Core, I would love a copy of you file.
Thanks

bowhuntrrl,

I had a new Savage 12 heavy barrel SS last year in 270 WSM. The initial bolt lift was hard and the WW 150 gr Power Point factory loads chronographed 3223 fps which is a little over what the book says the 270 Weatherby should do.

My case head expansion was .0025" on new brass!

I am on Ray Atkinsons side on this one. I find that case head expansion on new brass does correlate with other pressure signs.

As to the recoil of the 270 WSM it was about normal for a load that powerful. The Savage did have a soft but thin pad.

Hot core send one to me as well. jteljet@new.rr.com thanks!

Hotcore,

I would appreciate a copy of that file! More information can never hurt. Thanks.

bowhuntrrl@excite.com

If you prefer opinion over rigorous experimentation, go to the source of the opinion. Here is Ken Water's opinion of the PRE method, taken from his "Pet Loads" article. Ken clearly says that PRE does not qualify as a measurement system, and that it is inferior to both the strain gage and crusher methods.

Quote:

---

Ken Waters, �Developing Pet Loads�, Sep. 1982 Handloader magazine, p6a ff.

�Controlling pressure is therefore a major concern for handloaders, but to control it, we must first have some means of judging the height of its peak. Ballistics laboratories utilize special pressure barrels and copper or lead crusher gauges�or, alternatively, electronic transducer strain gauges�to measure chamber pressure. Such systems, however, require both costly equipment and skilled technicians, placing them beyond the reach of individual handloaders.

Even if we had a pressure-barrel setup and knew how to use it, that still wouldn�t tell us how much pressure that identical cartridges would develop in the barrel of our favorite sporting rifle or the cylinder of our favorite revolver, they being so entirely different in factors that affect pressure as well as in their abilities to withstand chamber pressures.

I have agreed to explain in detail the system that I�ve been using for some thirty years in developing handloads totaling countless thousands of rounds for a variety of both standard and wildcat cartridges. It has yet to let me down.

Two terms that I use are somewhat different from those in wider use concerning the same concepts�developing rather than working-up loads, since it is frequently necessary to work down from early loads and unsafe to work up; and judging rather than reading pressures since any such method is far too inexact to qualify for any term such as reading that implies a greater precision than is actually the case.

Now of course, no such system of judging pressures can reveal the actual pressure in pounds per square inch or copper units of pressure. It must be understood that this is only a means of determining comparative pressures, with nothing more to be expected of it. With the data provided, the pressures of my handloads can be classified as moderate, normal, near maximum, maximum, or excessive�which is all that is necessary to ensure the safety of the shooter.�

---

The only objections Ken raises to the strain gage system are cost and the skill required to use them. Advances in electronics have solved both those problems for us.

So if Hot Core wants to claim that the strain gage system is uncalibrated (ridiculously untrue), and therefore worthless, then, according to his idol, the PRE method is even more worthless, because Ken said that PRE is inferior to a strain gage. He also clearly says that PRE is uncalibrated: "It must be understood that this is only a means of determining comparative pressures..." i.e., a relative system only, not an absolutely calibrated one.

So, if you prefer opinion over data, the most authoritative opinion available is that PRE is an inferior, uncalibrated method.

If you prefer data over opinion, PRE and CHE require so much averaging to extract useful information, that they are impractical. You can be far past a safe load, and not detect it.

I agree that case head expansion is one way that reloaders can try to measure or "compare" pressure. A chronograph should be your first tool along with primer signs and the bolt firing pin hole leaving marks on the head. All these signs should be watched. Case head expansion measurements need to be taken all the way around the case and not just one place. Here's the results of one test I did on 50BMG cases fired in a bolt action rifle.
All loads used the same lot of brass and powder. 647 grain ball bullets, WC860 powder.
1. 795.4" ---size of unfired full length sized case head
2. 796.9, 797.2, 796.8, 797.5--purchased, remanufactured ammo using the same year and make of brass as used in all the test, loaded with 230 grains of 860--2920fps average
3.795.6---205 grains of 860 powder--2370fps(low velocity)
4.795.9---210 grains of 860
5.796.1---215 grains of 860
6.796.2---220 grains--2777fps (velocity goal)
7.796.4---225 grains--2847fps (pressure signs ok but warmer than I want to load.
8.795.6---200 grains of IMR5010 powder
9.795.4---210 grains of 5010
10.796.2--215 grains
11.796.1--220 grains
12.796.3--225 grains
13.796.4--228 grains of 5010
14.796.2--210 grains of 860 with 700 grain AP bullet
15.797.1--220 grains of 860 with 700 grain AP bullet
This is one test but does show that case head measurement is useful. I know that the 50 bmg case is large but this measurement is also useful on smaller calibers. All measures are thousandths of and inch measured at the case head just in front of the extractor groove.

rg1,

No offense, but I suspect you aren't good enough with the micrometers to distinguish 0.0001"! If you are then your brass must be softer than dog turds!

Do you have ANY idea what the pressure level has to be to PLASTICALLY DEFORM a 50 BMG case head. Understand that in order for you to be able to measure a difference in case head at all IT MUST FIRST PLASTICALLY DEFORM!

Here are some numbers for you.

1/2 hard cartridge brass (50 BMG) min. yield strength 42 ksi
Chamber pressure required to yield case head - 60,600 psi

3/4 hard cartridge brass (50 BMG) min. yield strength 55 ksi
Chamber pressure required to yield case head - 79,300 psi

Full hard cartridge brass (50 BMG)min. yield strength 65 ksi
Chamber pressure required to yield case head - 93,800 psi

So as I said, IF you are in fact measuring a difference in CASE HEAD DIAMETER after firing a round either:
1.) Your loads are off the map pressure wise
- or -
2.) Your brass is very soft (at least 1/2 or softer)

So you are either over pressure or your brass is junk.

ASS_CLOWN

No offense either A-Clown but your conclusion about my being way overpressure is wrong. While I have no way of testing, my brass is not soft. My mike measures in tenths of a thousandths and I am well capable of reading it. Perhaps you are not aware of where I'm measuring the case. I measure in front of the extracter groove toward the case mouth, not the extracter "rim" next to the case at the primer end and not inside the extracter groove itself.
As a follow-up to my previous post:
I would "NOT" keep adding powder until I got some measurement anywhere on the case that duplicated some factory loaded round. There are too many variables to rely on this for developing a safe load. Start by using "published" reload data. I'd compare published data with velocity results. Measuring case expansion is just one "clue", such as comparing primers, velocity, brass flow into primer ring on bolt, ease of bolt lift and extraction, primer pockets expanding causing loose primer pockets, etc, etc. Get a chronograph and rely on published data using the components that you use. What I've read concerning hard bolt lift after firing is scary. Pressures usually have to be quite high to cause hard bolt lift. There are too many variables to rely on case head expansion alone to develop a safe load!!

rg1,

Then sir you WEREN'T measuring the case head! You were in FACT measuring the case body forward of the case head, in the area correctly referred to as the "Pressure Ring".

I will post some pictures of the difference and why one is "OKAY" and the other is bogus tonight.

The numbers I posted ARE MORE ACCURATE than any micrometer reading! That is a fact. The laws of physics don't care about opinions, fads, or anything else for that matter. So if you had been measuring in the extractor groove, WHICH IS WHERE YOU MEASURE FOR CASE HEAD EXPANSION, the numbers I posted would have told the tale (not 100% but would have provided a bare minimum pressure, which in reality the pressure was higher, but once plastic deformation occurs the pressure calculations become MUCH more complicated as you are dealing with non-linear stress analysis).

ASS_CLOWN

A_C brings up an interesting point.

A considerable amount of what I have seen referred to as " case head expansion " is actually measured forward of the case head, and is not actually measuring the case head itself.

The area where the measurement is taken is nonstandard.
This measurement also would be somewhat varied for different diameters of cases. The diameter to wall thickness ratio would need to be taken into consideration to make this an accurate measurement when applied to different cartridges.

I think any of the above methods are useful in a " this is more than that " kind of way. But , none are really usable when applied to everything.

The key to safety is to stop increasing the powder charge BEFORE you blow something up. Any method that does this is good by me.

I have been guaging loads by comparing the amount of shoulder movement. Also a " this is more than that " kind of thing, but it seems to be consistant for a given combination of chamber and brass. And the results seem to give meaningful changes in measurements before anything bad happens.

Travis F.

"The area where the measurement is taken is nonstandard."

Sounds like we are not talking about the same thing in every post. Someone called it the "Pressure Ring". I measure the fattest part of the case body. This will occur something like 1/8" to 1/4" ahead of the extractor cut. The brass case walls are rapidly getting thicker at this point, approaching the solid head. If you increase the powder charge you will expand thicker brass. The brass thickness tapers one way and the chamber tapers the other. More pressure makes the brass expand closer to the case head. You can plot the increase of expansion on a graph. More powder makes a larger measurement. It happens in a repeatable and predictable way.

All that said, I know we are not measuring pressure. We are measuring what the pressure did to the brass. This is the same kind of thing as a crusher, we are looking at the pressure's ability to permantly bend, or crush, metal. Seems to me that the important thing is not the actual amount of pressure but the amount of "damage" it did to the brass. The brass case is the limiting factor. If my loads stress the brass the same amount as the factory ammo I am pretty happy. I have duplicated the stresses that the factory boys and SAMI, with all their fancy equipment, have determined to be appropriate

Scot,

Actually the case wall are rapidly approaching a radius at the base. This rapid increase in radial stiffness concentrates strain energy (read deformation) into the area we all affectionately call the "pressure ring". See the pictures I have posted of sectioned cases on my thread "Some Insight into Case Head Expansion" or something like that!

ASS_CLOWN

Now rg1 brings something good to the discussion: DATA.

Data have credibility. Opinion bows to data. Theory bows to data. I bow to data. Data bows to dang little else.

If you have several loads, with different amounts of the same powder, the same bullet, same or similar barrel temperature, and the resulting muzzle velocity and brass dimension, would you please post it? The stuff you put up before was tantalizingly close to having all the needed info. We'd need maybe half a dozen examples for what I have in mind, which is just an analysis of the data, and not a slam on anyone.

Measuring MV is a very prudent thing. A good chronograph will repeat within close to 1 fps, and is usually the most repeatable piece of test equipment a shooter can easily get. For repeatability, it beats the pants off a good balance scale, and a strain gage pressure system, for that matter.

I really worry about guys using pressure ring expansion, though. Your results will vary considerably, depending on the condition of your brass. It is easily possible to get brass that will not expand at all, at pressures well over a safe limit. I know of no practical way to judge the consistency or condition of the brass. Sometimes .0002" means you're OK, and sometimes it means that you are saving up for a rifle bolt implant in your forehead.

If you graph either PRE or CHE vs. actual pressure for several different powder charges, you get a definite trend. There isn't any question about that. If you have a trend, the model has predictive value. The problem is that the data are so widely scattered around the trend line that it's hard to estimate pressure, unless you have a whole lot of data, to "average down" the noise. There is more random noise than information in the data.

So can PRE and CHE be made to work? Absolutely. You can also count the sheep in a herd by counting the legs and dividing by four. If you want to do it that way, and you require an estimate as repeatable as the old CUP system (which was no prize of a measurement system), the actual math works out to averaging 140 rounds to get a standard of comparison. Once you have that, a 10 round average will give you about 10,000 PSI resolution, if your brass is like the batch I tested. So in an '06, you can't tell if your load is hitting 55,000 PSI, which is fine, or 65,000 PSI, which isn't.

So if someone wants to check brass size, fine. Without averaging, it has enough resolution to just barely distinguish a plinker load from a barrel buster. That's two categories, and just not terribly useful. With enough averaging to get decent repeatability, the method becomes much too much work, as compared to alternatives.

I'll resend by 9:30AM 18Jun04.

There four other folks I've had considerable trouble communicating with for the past couple of days now. I really think it is in Hotmail. But, you will eventually get it.