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Water capacity of cartridges

This is a discussion on Water capacity of cartridges within the Reloading forums, part of the Firearm Forum category; I don't understand the use of the weight of water in grains to measure case volume as it would relate to powder. I do realize ...


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Old April 24th, 2017, 12:47 PM   #1
 
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Water capacity of cartridges

I don't understand the use of the weight of water in grains to measure case volume as it would relate to powder. I do realize that value would differentiate volumes between the brass of the same cartridge but different manufacturers.



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Old April 24th, 2017, 01:16 PM   #2
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Bob Lewis, Water weight (in grains) has been the common way to measure case capacity for many years .... even QuickLOAD uses it. A simple procedure .... weigh a sized empty case with the spent primer sill in the pocket. Fill the case with water and weigh it again. The difference will be the case capacity. To get a fair comparison, cases must be trimmed to the same length.

Most "same cartridge" brands of cases will have near identical case capacities .... close enough where there won't be any significant pressure changes. Military and NATO cases tend to have thicker brass so the case capacity compared to a civilian case is about a 1% difference. This can change chamber pressure by about 1000 psi, assuming the same powder charge.

Last edited by Iowegan; April 24th, 2017 at 01:19 PM.
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Old April 24th, 2017, 02:12 PM   #3
 
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Thanks lowegan. I knew it had been around for sometime it just struck today to ask about it!
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Old April 24th, 2017, 06:56 PM   #4
 
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Quote:
Originally Posted by Bob Lewis View Post
I don't understand the use of the weight of water in grains to measure case volume as it would relate to powder. . . .
Water is assumed to have a standard bulk density, ie, weight per unit volume. By providing the water weight capacity, QL (eg) can calculate the internal volume.

The rest of us just use that water weight as a surrogate for comparing one case's capacity to another.
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Old April 24th, 2017, 08:08 PM   #5
 
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Thanks Twoboxer, I actually had made that assumption. I was curious as to whether there was a more technical reason.

Last edited by Bob Lewis; April 24th, 2017 at 08:10 PM.
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