Home Forums Reloading Big Game Rifles Measuring case head expansion

Gene,data needed is bullet type (brand) and weight,base shape and whether or not moly coated,bullet length, case capacity of water at overflow in grains weight of H20,cartridge length (overall length loaded with bullet you will be using,powder type and barrel length.Can factor in temperature,altitude if you think it will be unusual such as really hot.

Jn316/ I have a .300 Macdonald,which is an improved 300 Win. It also takes two firings to get the case properly formed, with neck turning after the first firing. This method of measuring case head expansion, has worked well for me, as well as the man who designed the cartridge. He has built quite a few rifles in this caliber, as well as three other calibers on this improved cartridge.<BR>Most times the people having their rifles rechambered, or rebarreled, will get him to<BR>form the brass as well. He has fired countless thousands of rounds, using this method with no mishaps.<BR>After all of the discussion of this method being unsafe in the last few days, I referred to my loading log. <BR>In the log including the .458 & .375 magnums,<BR>on down, the loads I have chosen safe for my<BR>rifles, are usually two to five grains powder<BR>less than the load book maximums. One example<BR>is for two .375 H&H rifles, a Mauser and a Sako, the load I chose to be a safe maximum,<BR>using the matching components, same lenght barrel, 270 gn X bullet, is the starting load<BR>in the Barnes manual. With two more grains powder, there were no visible signs of pressure, but only an increase of 30 fps and<BR>more noticeable recoil.The measured expansion<BR>was .00035",(one third of one thou.)so I reduced the powder to start loads. Accuracy was good at this point as well. My point being to all this, is if all my rifles have loadings below book maximum, and I do use the coinsiding manual,to match bullet make,<BR>there is measurable expansion, than I would<BR>have to think this method is safe.<BR>If you use Centurions info, new cases, and these measuring proceedures, you should come up with a load, that you have some confidence in. Hope this helps and good luck. <BR>PS. If the first firing does't completely form the case, there is a good chance there is no measurable head expansion. If you confirm this ,than I would say you have a <BR>Mulligan.

A most interesting thread this has turned out to be. I for one and I'm sure most have come out with a little better feel for determining pressure signs. And its not just one sign that we should concentrate on. Pressure can show in any number of indicators. So we must watch for all of them.<P>Gene, the Gibbs cases may be formed from just about any 06 based case. IE: 30/06, 270, 280, 25/06 etc. The trick is to maintain a tight headspace on the first forming load because the Gibbs has about .10 inch longer headspace than the 06's. I start with necking down to produce a false shoulder thats really tight when chambered. If its not, I get too much stretch in the case just ahead of the web area and the case will separate in about 3-4 loading. When fired with some pistol powder and corn meal the shoulder is pulled forward and good headspace is produced. Although the shoulders do not yet have sharp corners. The next firing with a medium loading of 4831 and a 100 gr bullet fills everything out nicely. This case is now ready for testing. Hopefully the case has not been work hardened so much that it wouldnt be a reliable one for measuring case expansion.<P>Cannon, good to hear someone has been down the same thought processes as I. Your 300 widcat sounds very interesting. With a little luck I'll find some range time and test the case expansion thing with rounds that start approaching what I already know is very hot.....Ray<p>[This message has been edited by Jn316 (edited April 22, 2001).]

Cannon,<P>If you file down the rim on standard cartridges to get the base readings, how do you account for the slightly out of round chamber? <P>I mean if you chamber and fire a round then measure the base on the filed section or align the mic with the headstamp, how can you be sure that you aren't measuring the smallest expansion due to the tighter/stronger part of the chamber?<P>Wouldn't that create a problem of false readings unless the case is in exactly the same position every time you fired it?<P>Also I am curious about the comment in the Speer manual on p.55 <P>"New cases can give deceptive readings. The first firing of any case will usually cause more deflection of the brass than subsequent firings. At Speer, we start with once-fired brass so the initial deflection is already accomplished"<P>If I were to measure factory rounds, how do I compensate for the greater initial deflection of the cases? Doesn't this cause a false pressure reading right from the start because the expansion is based on brand new cases with greater deflection?<P>Speer also states that .ooo3 to .ooo5 expansion is generally accepted as representing pressures in the 5o,ooo C.U.P. range. How much pressure does it take to expand the case .ooo1, .ooo2, .ooo3 etc?<P>Turok<P>------------------<BR><B>Make it idiot proof, and some one will make a better idiot</B>

The more I look at this the more it seems it more accuratly be called "the case retraction method of estimating pressures".The idea that the brass always expands to the chamber wall and that pressures exceeding the elastic limit of the brass dont allow it to retract,thus resulting in permanent expansion,makes the speer statement make sense to me.<P>I'm probably too dumb to be confused!

Turok<BR>I'm not sure I understand the first part of your questioning, but I will make an attempt to answer what I think you are asking.<BR>The need to file the rim on standard cases, is to allow the use of a standard mic.(blade micrometer would work without filing, but is the equivelant cost of a new rifle. I see you are from Canada, so the cost of a Starrett digital mic. in six digits is $800.00 plus tax. Standard is $200.00 + tax in Canadian dollars from the House of Tools)<BR>The part measured, is the thick portion of web, just in front of extractor groove. This portion of web(I believe .200-.220") does not enter the chamber. <BR>If you feel that filing a very slight amount of the rim (as rim is slightly larger, usually, than the web)would somehow effect the measurements, than you could take the correct amount off, all the way around, by utilizing a lathe or perhaps a drill press and a file. Personally, I don't feel this to be necsessary. <BR>Turok, without meaning any disrespect, and the fact that I do not have access to pressure test equipment, I would suggest you give a call to the fine people at Speer.<BR>The number was posted earlier, and it is toll<BR>free number. They can perhaps clear up any or all questions you have.<BR>I did get the numbers you seek from a friend<BR>but of course, since this is second hand info<BR>that cannot be verified, I would preffer you get it directly from the source.<BR>In addition, my wife has a leg long list of spring season things to do. This, I have to take care of before I can apply some of this info to developing ammo for a new rifle, just built. As the bear season is upon us,I'm struggling to prepare. Thanks for your understanding. Canon <BR>

Cannon,<P>Please don't worry about offending me, I understand peoples limitations and the fact that these boards do not easily lend themselves to the 'tone' of a persons voice.<P>I would like to state that I am familiar with the proceedure of case head expansion. I have read a fair amount about it on the various boards, in the Speer, Nosler and Nick Harvey manuals as well as in Ken Waters Pet Loads. Like yourself, I have used it for a few years now. <P>Although I do not rely on it, I use it out of sheer curiousity and as a means to collect data for when I am able to purchase strain guages. I have found a cheaper setup that runs for under $3oo US. This is enough equipment to use on three guns. Obviously the less guns you use it on the cheaper it's going to be.<P>Anywho, what I was attepting to ask had nothing to do with the integrity of the case after the rim was filed, or the interference of the rim before firing. <P>What I was asking is more related to the idea of no chamber being perfectly round and that there are weaker points in the barrel steel that would allow for more expansion in certain spots of the case head.<P>Now if you measure only one spot on the case via filed rim, it would imply that all the cases were positioned in the chamber in exactly the same way every time. If it is not, wouldn't you get different readings (+/-) with the cartridges due entirely to the variations in chamber rather than those in the pressure? If this is the case then wouldn't that essentually throw off the accuracy of the whole process?<P>Turok<P>------------------<BR><B>Make it idiot proof, and some one will make a better idiot</B>

Turok<BR>Now that you have broken it down finer, I finally get it. This is a good point.<BR>Up until now, I was going on the assumption that my chambers were in fact round.<BR>One more variable to the long list. Some target shooters do in fact place their rounds in chambers, in the same position to make everything as consistant as possible from shot to shot. If one uses a referance line on the cartridge anyway, it would of course make it easy to position it in the chamber to eliminate this one variable.<BR>My old friend, who did advise me of the measurement method ,did not make referance to this point.It was discussed on the topic of benchrest shooting. I will confer with him about it, to get his views. <BR>Up to this point, with the rifles used, any readings I have taken, have corresponded to the increase or decrease of powder used.With the exception of some readings taking a large<BR>increase, with only a small amount of powder being added. This of course is where I would determine where I wanted to stay with my load for this round. I would agree if the chamber was in fact out of round, this could help increase(decrease) the measurement,and your suggestion of placing the cartridge in the chamber at the same position each time, is a good one. If this variable does in fact exist in my rifles, I would suggest it is of small enough significance to not have affected any of the loads, I haved deemed safe in my rifles. I also suggest relying on an average of readings from several firings, rather than a limited few. <BR> One day soon, I'm going to have to give my lady the bad news, and tell her the new Oehler 43 is on it's way. It is after all in the name of safety, right?<BR>Surviving this, a bore scope should be easy.

Sorry, guys, I meant to answer some of your questions long before now but got too busy stomping snakes in other places. Got pretty tired doing it, too!<P>One confusion that I meant to clear-up earlier is this one:<P>"I'm still trying to figure out your post,KEN,about a blown up rifle due to incorrect powder charge when the discussion was about case head measuring.Do you think we dont know rifles will blow up?"<P>I was sure I'd had a good reason to cite this pile of gun chunks and slivers in this thread but had to go back to see exactly what was the immediate context of my reference to it. I was sure that the context should've made it clear why I mentioned it. It seems clear enough to me, of course, but here it is for your second look:<P>"Cases already too hard to show 'excessive' expansion here (some, even at 80,000 lb/sq in.) are especially likely to become brittle in repeated firings and reloadings, and spew wild gas and bits of brass into a shooter's face. I have on hand now a rifle utterly demolished when half the head of the case blew back through the action. The rest of the case is still in the apparently unharmed barrel, but the receiver is in many pieces, and my friend still has one piece of brass in his face (a larger chunk was surgically removed)."<P>My point in that earlier post was that cases can (and do) burst and wreak a good bit of damage without bursting or swelling the barrel � that they can (and do) "spew wild gas and bits of brass into a shooter's face."<P>As an example of what wild gas can do, without bursting or swelling the barrel, I mentioned that "I have on hand now a rifle utterly demolished when half the head of the case blew back through the action. The rest of the case is still in the apparently unharmed barrel, but the receiver is in many pieces, and my friend still has one piece of brass in his face...."<P>Hope the point is clear now, and that you can see the justification for citing this once-was-a-rifle in this thread. It fits. If it's still not clear to you WHY it fits, please read that paragraph again until it's clear to you. I don't know how to make it any clearer. (Or I would.)<P>Shalom!

Well I just measured a number of cases and have taken both the largest and the smallest diameter. The cases measured here were fired in a semi-custom .338-o6AI on a Rem7oo with a Douglas premium barrel. The numbers are as follows:<P>Largest----- Smallest<P>.4673 ------ .4671<BR>.4673 ------ .4670<BR>.4674 ------ .4671<BR>.4674 ------ .4672<BR>.4673 ------ .4671<BR>.4672 ------ .4671<BR>.4674 ------ .4672<BR>--------------------<BR>-------Average------<BR>.4673 ------ .4671<P>I would like to point out that the method I used is in strict accordance to the method Ken Waters uses, which is the measuring of web expansion and not base expansion. <P>Notice the variations between the two. In at least one case there is a difference of .ooo3 and on average there is a .ooo2 difference.<P>Rather than assuming that the chamber is round, I suggest spinning cases as you measure to get the most consistant readings and reconsider the measuring of just one section. <P>And as I'm sure everyone knows, each chamber is different. Like anything else with handloading, rifle chambers are going to vari. Don't assume the amount, know.<P>In any event, I still wonder how the greater initial deflection of the new cases is going to affect the readings when we try to compair the numbers obtained from factory ammo to the once fired cases.<P>Turok<P>------------------<BR><B>Make it idiot proof, and some one will make a better idiot</B>

I just thought of this after I posted the last one. Why does this meathod of expansion measuring allow additional expansion over the factory load, when the people at the factories with testing equiptment have determined the safe pressures, which is an unknown amount to those without pressure equipment?<P>Wouldn't this meathod of be safer/better off by equalling factory expansion rather than exceeding it?<P>Turok<P>------------------<BR><B>Make it idiot proof, and some one will make a better idiot</B>

Some very good points are being raised in response to my original question;How do you do it? Here are some points I[ FWIW ] keep in mind:<P>1.One cannot prove a negative.Therefore,one man may prove to his own satisfaction that the method-however he interprets the mic readings-has merit.Noone can prove it is without merit.<P>2.Strain-gaging is not without it's detractors.<P>3.The people gathering data for publishing reloading manuals arrive at different conclusions using the same [ in some intances ]methods of measuring for chamber pressures.<P>4.Anyone interested enough to moniter his cases is not the sort of guy who is likely to blow himself up by using too much of the right powder.<P>5.A modern rifle action is PROBABLY--I said probably--not going to destruct at even 20 percent over maximum design pressures.I say this not because I have inside information,but because the practice of using proof loads would not have had any value unless they were in that range at least.<P>Just the wanderings of an idle mind. <P>

I give up. There's too much specious* "reasoning" here for me. I've shot all these points down, repeatedly, for months and years, and so have others, and they just keep cropping up and attracting ardent followers. The support is flawed and easily disproved, but you fellows are just too many for me. I'm simply worn out from trying to warn of the dangers that I fervently hope NEVER befall you. Others have already concluded that measuring web expansion is a weed idea that can't be killed, and I've finally reached that conclusion too.<P>Come to your own conclusions, mike cases to your hearts' content, and pray that you're as safe as you've convinced yourself that you are.<P>Shalom!<P>* "spe�cious (sp��sh�s) adj. 1. Having the ring of truth or plausibility but actually fallacious: 'a specious argument.' 2. Deceptively attractive."<BR>[American Heritage Dictionary]

Ken Howell,<P>I have read and understood (well most of them anyway - that math part from another thread still gets me ) your posts here and throughout the many threads that this topic has spawned, and I must say I agree with you. <P>I really wonder what the actual pressures are running at when such things as variances in case hardness, out of round chambers, steel strength, initial deflection, and human error in measuring are taken into account.<P>As I mentioned before, I am hoping to obtain strain guages in the near future. And while they do have their problems, the pressures obtained by measuring a consistant factor, like you have pointed out, should produce closer results than the measuring of an ever changing factor such as the case.<P>Turok<P>------------------<BR><B>Make it idiot proof, and some one will make a better idiot</B>

Turok / I would suggest that your measuring the fired cases has told you that your cases are out of round, and not necessarily the chamber.<P>This would be a very good reason to measure your expansion at one point exactly, and only<P>You are assuming that your chamber is out of round, because the fired cases are. <P>I just measured some Federal Premium .458 mag<BR>ammo, cause that was the first box I came across, with both fired and unfired rounds.<P>They were measured according to a Speer rep. just in front of the belt, even though this is contrary to what I've been told in the past. Normally I measure on the belt on magnums, I did it this way to match the method you used.<P>UNFIRED LOADED .458 FACTORY ROUNDS<BR>Largest Smallest deflection <P>.51130 .50945 .00185<BR>.50980 .50860 .00120<BR>.51125 .50845 .00280<BR>.51110 .50960 .00150<BR>.51095 .50865 .00230<P>Average deflection .00193<P>Fired brass from same box Fed..458<P>.51345 .51260 .00085<BR>.51320 .51265 .00055<BR>.51385 .51310 .00075<BR>.51405 .51350 .00055<BR>.51320 .51250 .00070<P>Average deflection .00068 <P>The average deflection is .00125 less after the cases were fired. This ironed out some of the wrinkles, but does it still mean my chamber is out of round? Or will this number decrease with progressive firing?<P>I would think a chamber casting be a more accurate method of checking the chamber for inconsistansies. <p>[This message has been edited by Canon (edited April 25, 2001).]

Turok / In answer to your post, and I hope this is my last post on this topic. The measurement method I described does not allow for more expansion than factory expansion.<P>In fact it is quite a bit less ,if the guidelines are followed. The factory .458 loads, measured on the belt were .0009". Just less than one thou. Speer suggested loads, going up to .0005", then reducing by 6%. A very generous saftey factor. WELL below<BR>published maximums. (Which is what Ken suggested days ago) <P>I built a load ,worked up with an Oehler 43<BR>PBL, by a Stan Skinner of Guns & Ammo, Feb.2000. He gives a list of loads ,that are a couple of grains under published loads, and the expansion with new cases are .0001"<BR>The expansion on subsequent firings should be nonexistant. It has an allowance built in for an unseasonaly warm hunt or climate.<P>If a person does need more velocity or more power, rather than load a round to the maximum pressures, go to a larger cartridge. <P>[This message has been edited by Canon (edited April 25, 2001).]<p>[This message has been edited by Canon (edited April 25, 2001).]

Working on the theory that no case is really round, and using the Ken Waters method of pressure ring measurement, I've been using my run out comparator, and working with the average expansion. I'm not exceeding the factory ammo expansion, but can understand how using factory ammo in an improved chamber could give you less expansion than the SAAMI pressure limits. I know I'm not using the very finest equipment available but am content that I can judge within a half a thousandth. As Waters stated his method helps you "judge" not "measure" chamber pressures.<P>As for the destroyed rifle, Ken Howell referred to, once the gas gets out of the case and into the action, destruction is nearly a certainty. I think Remington's theory of confining gas escaping from the case to the chamber area is the best solution. The Remington bolt face will obturate sealing the gas in the barrel, and preventing the damage other actions can experience. Of course you can't use the rifle again, but it beats not haveing the use of your head, hands or other parts of your body.<p>[This message has been edited by Slamfire (edited April 29, 2001).]

Please explain obdurate.I shoot remingtons.

The steel ring at the head of the bolt that surrounds the cartridge, expands outward, sealing the chamber from the rest of the action.

This has been an interesting thread, but I am more than a little curious as to how Remington manages to obturate the firing pin hole in the bolt face.