Home Forums Hunting & Shooting Ask The Gunwriters Case head expansion?

Mr. Howell, I'm just starting to work up 250 Ackley loads in a modern bolt action and need help measuring case head expansion. My questions are:
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<br>1)What is acceptable case head expansion? I know you are usually supposed to measure a factory round as a benchmark, but factory rounds are loaded to about 44,000, while I intend to load up to 50,000. Any maximums?
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<br>2)Where, EXACTLY, should I measure on the case? I've heard to measure in front of the web, but, how far in front? After all, it is called case HEAD expansion, isn't it?
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<br>3)Is a blade micrometer necessary? I've tried to use my regular mic before and find it difficult to repeat the same measurement. Is there a trick to it?
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<br>I will, of course, heed all of the other traditional signs of high pressure, but since it's my understanding that measuring case head expansion is the most accurate way to gauge pressure (without sophisticated equipment), I'd like to develop maximum loads in the safest way possible. Thanks very much for any assistance you can give me.

Ken:
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<br>I have been hoping against all hope that this question would be asked of you.
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<br>I will come right out and say it. All of my admittedly limited experience demonstrates that case head expansion is NOT a definitive nor a completely reliable method for determing safe operating pressures. In fact, I have concluded that I should place no more stock in case head expansion than I would in the other telltale pressure signs taken individually. To me, CHE is one more thing to check. Nothing more, nothing less.
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<br>What say ye?
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<br>Flamesuit firmly affixed.
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<br>Rick

I've got Bob Hagel's old book, "Game Loads and Practical Ballistics for the American Hunter."
<br> Great book. He talked alot about various bullets, and how they behaved in the game fields. Started my thinking towards the premium bullets, like the Nosler Partition.
<br> Also a good discussion on using case head expansion to determine maximum loads. He'd go up in powdercharge until he got a trace of head expansion, then reduce about one grain. Two grains in larger, magnum cases, etc. Later, he would record the number of times the cartriage case had been reloaded. He figured if he got 8 reloads, he was OK.
<br> From what I gather, he did this testing under "standard conditions", like 70 degree temperatures.
<br> When shot under warmer conditions, the pressures developed would go up, of course. I suspect a bit too much.
<br> The system doesn't take into consideration the variation in brass quality. It is not easy to use consistantly.
<br> I don't use this system. I don't like the difficulty of using it consistantly. I don't think it gives enough lattitude for variations in temperatures, and other factors. For instance, if your "maximum loads" sit around for a few years, the bullets have a tendency to bond with the case neck. You will need to "break them loose", by seating them a smidge deeper, to prevent higher pressures. Or so I've been told by a chemist/hunter friend once.
<br> I just don't like being that close to a stuck case. I've had good, but hot loads, when left in the sun, on a hot day, suddenly blow a primer, or stick a case.
<br> In a nut shell, his levels of acceptability are just too hot for me, and my uses.
<br> When I got a computerized ballistics program, I discovered I can do just fine without that last 100-150 fps. And extra accuracy is nice to have, which often accompanies lower pressures. E
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I tend to agree with you that it is one of several conditions that should be examined. It is though one of only a few examinations that the average loader can do which is numerically quantifiable if you have the factory load expansion in the same make of case etc. and can be compared. That being said it is not an absolute and any number of factors may affect whether you wish to stop there or even before there.
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<br>One current writer primarily has espoused it and I think most people reading his data will find it generally safe used in rifles comparable to his tests. He was not the first to use or report it though. I'm sure he anticipates other people are liable to exceed his reported data and they may have to just to achieve the same pressures in their rifles.
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<br>However when you use his data you know exactly what parameters he is basing it on. Other writers frequently present data with no parameter other than it didn't blow their rifle up and no indicators of the workup(ie: a number of single data high level load combinations for whatever was being tested These fellows are really hoping Joe Average who ever he might be has sense enough to proceed in an organized manner for his own safety and be able to evaluate the results.
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<br>I use the measurement and find it a relatively dependable indicator in some cartridges but do not rely on that criteria alone by any stretch of the imagination.

In the fall, during my first few months at Westinghouse Ordnance, the division secretary asked me to specify when I intended to take my vacation the next year -- nearly a year in advance. I said I had no idea -- yet -- when I would want to take it and would promptly tell her as soon as I had some idea when.
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<br>"I HAVE to have some definite dates, NOW," she said.
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<br> I said I didn't want to commit myself to dates that wouldn't be the days that I'd eventually want to take off.
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<br>"But you won't be held to the dates you give me now," she said. "You can change 'em later, any time."
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<br>I couldn't believe what I was hearing. I asked why it was necessary to specify dates that wouldn't be binding.
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<br>"So we'll know -- now -- when you plan to take your vacation."
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<br>"But if I can change 'em, any time--"
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<br>"You can."
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<br>"--then what can they possibly tell you?"
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<br>"When you plan to take your vacation."
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<br>Miking case expansion, ANYWHERE on the case, tells you just one thing --
<br>-- how much your case has expanded at that point.
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<br>Any other conclusion that you draw from that expansion comes from unreliable assumptions already established in your brain, not from any scientific or safely reliable basis of how that expansion relates to the peak internal pressure that produced it.
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<br>The "reasoning" behind this procedure (which I supported and defended for decades before pressure tests showed me the errors of it) also reminds me of the realization that first shook my faith in the "theory" of how slime evolved into humans. Our university class was learning the discipline of the scientific method, including the distinctions between a hypothesis, a theory, and a scientific law, and how scientific study proceeded to advance from one of these stages to the next. I realized, FWIW, that Darwin's brief observations had led him to conjecture a hypothesis that we now call a theory and treat as if it's a law even though it's still only a hypothesis -- not even supported by the body of persuasive evidence that would refine it into a valid theory, and certainly lacking the incontrovertible evidence that would properly establish it as an incontestible law of nature. People believe it and accept it as a a law of nature simply because they want to believe it, not because science has (by proper use of the scientific method) properly established it. Science hasn't thus established it.
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<br>So it is with miking case expansion. It tells you only how much your case has expanded -- nothing more, because there's no real, reliable way to quantifiably relate peak internal pressure to case expansion. No way, that is, to interpret so many ten-thousandths of an inch (of case expansion) as having been produced by so many tens of thousands of pounds per square inch (of peak pressure). This alone is enough (for me) to disqualify miking case expansion as a reliable, useful safety procedure.
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<br>Worse is the fact that in a number of experiments with pressure barrels, case-expansion measurements have indicated "safe" pressures with loads that the pressure guns identified as proof loads (or even hotter).
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<br>The rest of you can take this from here, wherever you want to take it. I'm tired almost to death of the squabble that inevitably comes into any discussion of miking case expansion, and I want no further part in it. What I've just related is well known and repeatedly shown to be true -- accepted by the prudent, hotly condemned by others. Take it or leave it. The rest of us have other, more interesting matters to discuss. This thread is likely to go down in flames, and I'm in no mood to don an asbestos suit or to wield a torch.

Ken.....well put including the "example"! It's always amazed me how some shooters will hold onto something that was said decades ago by those without access to proper equipment or the ability to understand it if they did. Not only does the expansion-measurement mean little, I don't think 1 reloader in 100 can use a micromenter well enough (or have a good enough micromenter) to get good and repeatable readings.

DB Bill- I am most definately one of the 99 who can't read a micrometer well enough, even if the methodology was accurate. I have tried both a standard micrometer and even a borrowed digital that reads to 1/2 of one ten thousandths of an inch. Marking the case so I try to measure in the same place, I can't even get the digital to read exactly the same thing twice in a row. I just can't get the feel of it.

Mr. Howell, thanks for your response. I am aware some people do not subscribe to CHE measurement as a gauge of pressure. I am also aware that some people do. Unless someone will inform me of a definitive method of measuring pressure (within my modest means) I will continue to try to use it, along with the other indicators of pressure. Enlarged primer pockets are not a definite indicator of pressure either, but I still pay them heed. As for pushing the limits of a small case, I have no intentions of pushing the limits. That is precisely the reason I would like the ability to accurately gauge the maximum pressure that the cartridge is generating, to avoid pushing the limit. As for purposely loading 100 to 200 fps below maximum, how do you know what the maximum is in your gun? Do you carefully increase the load until pressure signs appear and then back off? I have developed many loads that shot most accurately at, or near, maximum. If I were unwilling to explore the capacity and capabilities of the cartridge, I would simply use a factory round.
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<br>I'm just trying to utilize every method available to measure pressure, in an abundance of caution, to assure the safe development of loads in my gun. I'm sorry if some feel it necessary to admonish me not to load within several hundred fps of maximum, or to air their private pet peeves. I have no intention of playing little flame games.
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<br>I thank you for your response, Mr. Howell, as I have been an admirer for quite some time. I understand your position. I will continue to look for the answers to my questions elsewhere. Thank you for your time. Jim

WOW! I guess we can categorize that as an "I don't like your answer so you must not know what you're talking about" response. I wonder if he drives his car at 6000 RPM too.

DB Bill, you're certainly welcome to catagorize my response any way you want to. I was extremely appreciative of Mr. Howell's response and I said so. As for not liking the answer to my question, exactly what question of mine did you answer? And where did 6000 rpm come from? Did you even read my post? I would suggest that next time you confine your responses to topics that you know something about. You'll look less foolish.

I guess I should have remembered the old adage of "letting sleeping (old) dogs lie".

<br>Gentlemen - As most folks agree, case head expansion is not an accurate gage for pressure. Case head expansion becomes more apparent with work hardened brass, verses new brass which exhibits some degree of spring back. As the thickness and condition of the brass changes, so does the stability and repeatability of case head expansion.
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<br>HOWEVER, it is one sign you must consider. Case head expansion signs combined with accurate chronograph data, the condition of primers, marks imparted on the brass by the bolt face and extractor, bolt handle lift, and ease of extraction will point to more accurate information. All chambers and bores are different. If you use a chronograph for long you will understand that not all things are equal. A hot load in one rifle may produce no pressure signs and yet dangerous pressure signs in another. If you are not shooting across a chronograph during your load development, you are missing one of the best indicators for what is happening within your chamber.
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<br>If you carefully measure the water you mix with the ingredients necessary to bake a cake and simply toss everything else in the mixing bowl and set your oven 120 degree higher than directed, you will most likely not be please with the results - sorry for the cake analogy, I have not eaten this morning.
<br>As a hand loader, you cannot focus on one step in 25 and hope for accurate results. You cannot take case head expansion as the single deciding indicator for safe pressures. If you do, you may find yourself in the middle of the Kaboom table sooner or later.
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<br>BTW - I believe DB Bill�s points were valid. Maybe they were translated the wrong way.
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I know we are trying to help one another and this is a particularly important area of the handloading experience.
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<br>For what it's worth, I have always considered "case pressure" to be a moot point. What is important is the ability of the case to withstand/contain the pressure developed when the round is fired.
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<br>50,000 psi may be safe in brand X, but not so in Y, if the Y brass is softer/less able to contain the pressure. And brand Z may be able to handle more than brand X. It is a well known observation among handloaders that one batch of brass will handle heavier loads than another in the same rifle, even from the same manufacturer. The "weak link" in the system is the brass case.
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<br>I am currently working with a 270 Wby that is giving exceptional velocities, and using Federal nickle-plated brass in this load development. Another forum member, 1886, had cautioned me that his experience with nickle-plated Federal brass had been that it would not take as heavy loads as the Wby brass in his rifle.
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<br>I have not used any Wby brass, yet, but clearly, in this rifle the Federal brass is doing well. The primer pockets are still tight after three loadings that give 130 gr spitzers over 3500 fps out of a 24" bbl. Now you don't get that kind of velocity without some fairly skookum pressure.
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<br>My own method concerning case head expansion has developed into the following rule for me: good case life and primer pocket that remain tight with repeated loadings indicates a safe load with that brass in the particular rifle, not cartridge, being loaded for.
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<br>If I change the brand of brass, or even the same brand but a different lot, I had better start over and work up the loads again. Certainly if I use a different rifle, it is paramount that I start over. Have been loading for more than three deades and never blown up a rifle, but have had a blown primer or six. That was a long time ago. Today as soon as primer pockets became even a little bit loose, that's it! The load gets reduced by 5% or so, usually 2-3 grains, and that's where it stays.
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<br>Hope this helps,
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<br>Ted

Of course case head expansion is a method of measuring pressure. If the primers fell out of the pockets you would be certain that the load was too hot for those cases.
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<br>Not many of us have a mic. with the right anvils for the job nor the ability to use it if we did.
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<br>I have Hagels book and he was treading on the edge as pointed out above. But Bob Hagel was/is a very wise man. Somehow I am certain he kept track of things and got the most out of his rifles.
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<br>But it's a much better idea to have a wide margin of safety. If that .250 I is not fast enough just buy a bigger gun.

I have noticed, all my life, that no matter what you say or do someone will argue about it. Make a statement and someone with take umbrage to it. If it has anything to do with anything written in the past it is now LAW and there are those who will die fighting over it without ever thinking about changing or EVER thinking about questioning it. Just make any statement about a certain long dead proponent of a certain favorite cartridge and see what happens. It is totally ignorant, but that's us. I have found the enemy and he is US. I think nature endowed Homo sapiens with a predetermined genetic response to attack everything in sight. It's a wonder we have survived as long as we have. Hey, don't go there! It does get very tiresome if you want to pass on information and it happens on every forum I go to. It's worse than Saturday night at a bar or a hen house parlevous. I have found that when someone asks a question they usually have the answer ready and really only want a verification of their position and if they don't get it, Katy bar the door. Some know everything and what you say doesn't matter.
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<br>There are many ways to judge when the pressure is getting close to the pucker factor and all those factors have been hashed out and stomped to death on many fronts. Only a few have the sense to use them all, think about them, evaluate and stay safe. It's one of natures ways of weeding out the populaton and the undertakers need the work.
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<br>It is really hard on the newbys. Like running into a firefight with your pants around your knees. They have to dodge bullets while trying to learn enough to stay alive. Who do you believe. Look at the world, then at a playground. The only thing different between them is the size of the weapons and the strength of the armys. We humans have an incalculable capacity for learning yet we have sh** for brains sometimes.

After all is said and done what is the correct method of judging pressures for the handloader? Banter back and forth is great but if any of you were going to explain the methods of judging what is safe and what is not how would you go about it? Lets say that you wanted to get the most from your gun at safe levels. I know we could take the lowest max loads in the many reloading books for our bullet weight and stay 10 percent below it and say that is safe but lets work on up to the high end and explore the higher end of velocity. What is the correct way of determining the max load for your rifle or handgun? This is for the sake of discussion ok. Also lets not get into whether 100 fps makes any real difference because it really doesn't as long as you have accuracy. I know all that. Lay it on me as I am sure I will have many more questions.

I believe the best way of determining the max load for any given rifle is to purchase the Oehler system that utilizes a strain gauge affixed to the barrel of the rifle and measure the pressure with that system.Since I have been unable to afford that equipment but wanted to know the pressure generated with my loads I opted for the Quickload computer program.Not perfect, but amazingly accurate. I have also decided to back away from the max in my rifles; never have been particularly lucky and wish to keep all body parts intact if possible.Regards,Frank

I think folks have a real hard time grasping that it is possible to measure something, but that measurement may be meaningless to what it is they are tryin to determine.
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<br>How about if one were to use a chrono, and find that they were achieving 2700 fps with a 180 gr bullet in a 30-06. Would that measurement correlate to a safe load? The aswer is, NO! The measurement does not take into account the type of powder and quantity of powder, or barrel length, or brand of bullet, so by itself, is a meaningless number, maybe the load is safe, maybe the load isn't, but the velocity doesn't tell you.
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<br>So it is with case head expansion. You can measure it, you can see it increase with increased charges, just as your velocity rises, but the number you measure does not correlate to pressure. It would be wonderful if this number was useful in determining safe loads, but the fact remains, it isn't, and it doesn't, no matter how much stock we take in it.
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<br>A chronograph used in conjuction with published, tested load data provides a fair level of safety, is relatively inexspensive, and relatively easy to use. If you want a higher level of safety, then invest in a strain gauge device. If you wish to hold on to case head expansion as a means of determing pressure levels, despite laboraty tests prooving the fallacy of that method, then that is your choice, though a curious one IMHO.