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 January 1, 2011, 02:26 AM #1 HiBC Senior Member   Join Date: November 13, 2006 Posts: 3,057 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, 02:40 AM #2 egor20 Senior Member   Join Date: November 14, 2010 Location: Northern Virginia Posts: 1,744 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 __________________ Chief stall mucker and grain chef Country don't mean dumb. Steven King. The Stand
January 1, 2011, 03:27 AM   #3
Lost Sheep
Senior Member

Join Date: January 24, 2009
Posts: 2,766

Quote:
 Originally Posted by egor20 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 __________________ Chief stall mucker and grain chef
Of course, ON the moon (whether full or not) wouldn't the powder charge weigh one-sixth what it would weigh on Earth?

Quote:
 Originally Posted by HiBC I have a question. (edited for brevity) Or,am I overlooking something?
Begging your pardon, I mean no offense, but I don't understand. The only question you asked was that last sentence. There was no other question in your post.

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

 January 1, 2011, 03:29 AM #4 Hog Buster Senior Member   Join Date: October 26, 2009 Location: Pointe Coupee, Louisana Posts: 751 Eureka! __________________ Those who beat their guns into plows, will plow for those who don't.-Thomas Jefferson
 January 1, 2011, 05:40 AM #5 WESHOOT2 Senior Member   Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 13,036 W T F? Case internal volume differs. No assumptions required. __________________ . "all my ammo is mostly retired factory ammo"
 January 1, 2011, 06:01 AM #6 HiBC Senior Member   Join Date: November 13, 2006 Posts: 3,057 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, 07:12 AM #7 Sport45 Senior Member   Join Date: May 26, 1999 Location: Too close to Houston Posts: 3,987 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. __________________ Proud member of the NRA and Texas State Rifle Association. Registered and active voter.
January 1, 2011, 09:27 AM   #8
MrBorland
Senior Member

Join Date: May 31, 2007
Posts: 1,454
Quote:
 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 density of brass is the density of brass, so as you pointed out, whether 100 grains of brass is melted into a ball, or rolled into a flat sheet, it'll still displace 0.8ml of water. But introduce a "variation" into either surface, and it'll still displace 0.8ml water as long as the variation hasn't removed or added material. If more or less than 0.8ml is displaced, it means material has been added or removed, respectively, which you could've figured out with a scale.

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 09:38 AM.

 January 1, 2011, 10:35 AM #9 Brian Pfleuger Staff   Join Date: June 25, 2008 Location: Central, Southern NY, USA Posts: 14,667 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. __________________ Still happily answering to the call-sign Peetza. --- You do not HAVE a soul. You ARE a soul. You HAVE a body. ----- He is no fool who gives what he can not keep to gain what he can not lose. -Jim Eliott, paraphrasing Philip Henry.
January 1, 2011, 03:37 PM   #10
Shoney
Senior Member

Join Date: February 21, 2002
Location: Transplanted from Montana
Posts: 2,311
Quote:
 OK,The question is,am I overlooking something.
Your studies in English grammar. Your studies in punctuation. Your studies in logic. However, common sense cannot, well never mind.

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.
__________________
I pledge allegiance to the Flag - - -, and to the Republic for which it standsâ€¦.Our Forefathers were brilliant for giving us a Republic, not a democracy! Do you know the difference??? and WHY?http://www.wallbuilders.com/LIBissue...les.asp?id=111

January 1, 2011, 06:44 PM   #11
Lost Sheep
Senior Member

Join Date: January 24, 2009
Posts: 2,766
I think I get it, but still wonder, "Why?"

Quote:
 I have a question.
I am still not quite sure, but I think I've got it. You are analyzing the dimensions and volumes of the 223 Remington and 5.56 NATO cartridges and want to know if you have included in your list, all the possible significant factors.
Quote:
 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.
Yep. Inside dimensions of a sizing die would be a little smallish because it has to have some allowance for the metal to spring back to dimension. SAAMI dimensions are available. Dimensions of a chamber cast of your rifle would be most significant to you. The dimensions of a fired case would be a little smaller than a chamber cast, but larger than a sizing die.
Quote:
 Now,another assumption,cartridge brass alloy is similar enough to have the same specific gravity.
You don't have to make that assumption You can measure it with the same Archimedian technique.
Quote:
 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?
Have you found such a variation? One that is not explained by "missing metal" (extractor groove size variation or flash hole size variation)?

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

 January 1, 2011, 06:47 PM #12 Lost Sheep Senior Member   Join Date: January 24, 2009 Location: Anchorage Alaska Posts: 2,766 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, 06:52 PM #13 HiBC Senior Member   Join Date: November 13, 2006 Posts: 3,057 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, 06:56 PM #14 HiBC Senior Member   Join Date: November 13, 2006 Posts: 3,057 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
 January 1, 2011, 07:03 PM #15 WESHOOT2 Senior Member   Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 13,036 I don't imbibe Case alloy varies by manufacturer. Suggest solidified parameters and only one assumption per..... __________________ . "all my ammo is mostly retired factory ammo"
 January 1, 2011, 07:10 PM #16 Lost Sheep Senior Member   Join Date: January 24, 2009 Location: Anchorage Alaska Posts: 2,766 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, 07:38 PM #17 HiBC Senior Member   Join Date: November 13, 2006 Posts: 3,057 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, 10:49 AM #18 Hog Buster Senior Member   Join Date: October 26, 2009 Location: Pointe Coupee, Louisana Posts: 751 While the method holds water............... The practicality of it is all wet............ __________________ Those who beat their guns into plows, will plow for those who don't.-Thomas Jefferson

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