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January 1, 2011, 01:26 AM | #1 |
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case volumes and Archimedes bath
I have a question.
If we assume that the walls of the chamber,or a sizing die,or an engineering drawing define the outside surface definition of a cartridge case in theory. Suppose we just had this surface,no cartridge case.It defines a volume. Now,this model of the outside surface volume would contain x grains of water.Lets subtract the volume of the extractor groove,the primer pocket,and the flash hole. We will call this number the "adjusted gross cartridge volume" Now,another assumption,cartridge brass alloy is similar enough to have the same specific gravity. If I have 100 grains of brass cartridge case,whether thin,thick,or melted to a pellet,it will displace however much water 100 grains of brass displaces. Therefore,I suggest,if brass weighs the same,variation in the water capacity is more about dimensional variation in the outside condition of the cartridge case. Or,am I overlooking something? |
January 1, 2011, 01:40 AM | #2 |
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http://www.math.nyu.edu/~crorres/Arc...ath_600dpi.gif
Put 3 chipmunks and a pineapple, plus 30 grains of BP and ram it down the cartridge with a hickory stick on the Full Moon. Should work
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January 1, 2011, 02:27 AM | #3 | ||
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What's your point?
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There were several implied questions, but the one I guess you are after is, "Should I determine case volume by the water weight method before or after resizing?" My answer is to take a fired case (or a statistically valid number of them) and measure the volume. Then size the cases (without depriming) and measure them again. How much volume was lost? Did it match what you would have expected from the decrease in diameter of the unsized vs sized cases. I suspect the difference between sized and unsized will be less than the difference between brands. Let us know, please. I am curious now. But I don't think it will make a difference to my loading activities. Now, if I was loading for 1,000 yard benchrest matches, then it might. Lost Sheep |
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January 1, 2011, 02:29 AM | #4 |
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Eureka!
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January 1, 2011, 04:40 AM | #5 |
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W T F?
Case internal volume differs. No assumptions required.
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January 1, 2011, 05:01 AM | #6 |
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OK,The question is,am I overlooking something.
The rest was trying to present the idea.It seems to me if two cases made of similar brass weigh the same,they will displace the same volume of water,as they will have the same volume of brass.That was Archimedes eureka moment.I suggest if they weigh the same and show different water weight of case internal volume it might really be that there is variation in the outside dimension of the cases. The application is in matters of comparing say,223 and 5.56 brass. Happy new year to you ,too |
January 1, 2011, 06:12 AM | #7 |
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The density of brass is much higher than the density of water. Because of this, you can't ignore the differences in extractor groove dimensions, etc. The tried and true case volume comparison is done by weighing the water held by a sized case.
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January 1, 2011, 08:27 AM | #8 | |
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Quote:
If you know 2 cases weigh the same, a displacement difference indicates they have difference densities from a slight alloy variation (assuming they're equally clean). Last edited by MrBorland; January 1, 2011 at 08:38 AM. |
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January 1, 2011, 09:35 AM | #9 |
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What you might be overlooking is that we're not interested in how much water a case DISPLACES. We're interested in how much it holds. Those two thing are NOT the same. The construction of two manufacturers case for the same cartridge is not necessarily identical One has thinner walls, one thicker. One has less brass in the head region and one has more. In other words, yes, if they weigh the same then they displace the same amount of water, that doesn't mean that they HOLD the same amount of water.
Anyway, it all seems like a lot of over-thinking for me, and I normally do a lot of over-thinking. Just fill a case with water and weigh it. End of story.
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January 1, 2011, 02:37 PM | #10 | |
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I would never assume, butt you should always remember that when a tree falls in the forest, and there is only one woodchuck nearby, the flutter of a butterfly's wing can, in the presence of atmospheric di-hydrogen oxide, disturb the cloister of the hyperbole.
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January 1, 2011, 05:44 PM | #11 | ||||
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I think I get it, but still wonder, "Why?"
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Don't overlook the fact that you could measure the volume of the case using the displacement (Archimedean) method both with the case filled with air and filled with water. And if you filled the extractor groove with a material having a specific gravity of 1.000, you could discover the volume of that space. I am not sure how accurately you will have to make dimensional measurements to figure out what you are trying to figure out, but I suspect it may be beyond capabilities of the typical handloader's equipment and techniques. I looked over some of your other posts and threads and you do not strike me as the kind of guy who would troll or start a thread with no purpose (on any other day than April 1, perhaps). Some question must have prompted your investigations. Care to share it? Lost Sheep Happy New Year |
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January 1, 2011, 05:47 PM | #12 |
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Impertinent question
After I re-read Shoney's post, I thought to question the obvious:
You post was at 9:26 PM on New Year's Eve. Is this a case of the curiosity genie being released from its bottle? Lost Sheep |
January 1, 2011, 05:52 PM | #13 |
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The internal volume is the external volume minus the volume of the brass.
Regardless of case wall design,from an identical exterior,200 grains of brass will displace the same amount of water,and reduce the internal capacity the same amount. If you take 2 WW .223 brass,once fired,that weigh the same,but were fired in different rifles,the case volume will vary.If you neck size one,and small base size the other,the case volume will vary.The internal volume varies because the external volume varies.The volume of the brass in the case remains constant. A round ball of cartridge brass will displace exactly the same amount of water as a cartridge case of the same weight. If the alloy is the same,if the extractor groove and primer pocket are the same,if the outside dimensions of the case are the same,two cases of equal weight will have the same internal volume.It does not matter how the brass is distributed,the weight,therefore the volume of the brass remains constant. Heat treat,hardness,and therefore springback vary,so running the brass through the same die may not produce identical exteriors. Anyway,seems rather hostile here.Not enjoyable.I'm done.Oh,Shony,you misspelled a word |
January 1, 2011, 05:56 PM | #14 |
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Lost Sheep,No,as a matter of fact.Below zero,bad night for walking,and NYE is a bad night for driving.I drank no alchohol.I did suspect alchohol had something to do with the replies
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January 1, 2011, 06:03 PM | #15 |
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I don't imbibe
Case alloy varies by manufacturer.
Suggest solidified parameters and only one assumption per.....
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January 1, 2011, 06:10 PM | #16 |
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What kind of propellant is that?
HiBC, no offense is intended from my side.
I did enjoy the mental image of 3 chipmunks, a pineapple and 30 grains of black powder. That would definitely be a "multi-base" propellant. Probably a compressed load, too. Again, Happy New Year, and I hope the source question has been illuminated. The practical application still eludes me. Lost Sheep |
January 1, 2011, 06:38 PM | #17 |
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Another thread brought up case volumes between military and commercial .223.
Water testing has its own variables .I suggest weight is a close enough measurement of internal volume. The water method is useful when figuring the bullet taking up space,as in for a softrware input. I have a hard time communicating some things.My trade was moldmaker. Pre-CAD,from flat,2-D drawings,I had to form images in my head like Solidworks 3-D models.Then,I had to envision the steel to make the part. Later,I learned Pro-Engineer.Using surfaces to subtract volumes,etc,all in a days work.Its not so easy to put in words. Thanks for digesting it enough to give a thoughtful response |
January 2, 2011, 09:49 AM | #18 |
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While the method holds water............... The practicality of it is all wet............
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