Case Capacity


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Blakenzy
January 9, 2007, 08:55 AM
Is there a simple yet accurate way of measuring a case's usefull capacity?

I think that this is important since accuracy depends on consistency and since there may be variations in cases of the same make and even of the same lot, it would be helpfull to know how consistent your brass is.

Also, I heard that one should not use commercial reloading data intended for use in commercial brass when reloading military surplus brass or cases with thicker than usual walls beacuse of the diminished capacity of these which could lead to a dangerous increment in pressure, so finding out if the brass you will use is within normal commercial specs is also good for safety.

I have read that you could weigh your cases and if they have different weights, but equall outside dimensions, then the heavier case would probably have thicker walls an consequently smaller capacity.

But what about filling cases with liquid and measuring the amount with a syringe? Could this work as well, and perhaps be more reliable? Are there other ways or is this just not critical enough to bother?

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JDGray
January 9, 2007, 09:05 AM
My Lees modern reloading manual, list the usefull capacity on each caliber:)

Idano
January 9, 2007, 09:22 AM
JDGray isn't that listing is by caliber and not by manufacture? I believe that Blakenzy is looking for the variation by manufacture.

Blakenzy I don't know of any convenient way to measure volume other then what you suggested nor have I ever seen anything published. Unless you're a bench rest shooter or load your ammo extremely hot I doubt you'll ever see any variation. I have reloaded and shot mixed head stamp, commercial and military, out of my Model 70 in 30-06 and never have seen any variation on paper

armoredman
January 9, 2007, 09:57 AM
It has been done exactly that way, Blakenzy, called grains of water measurement. I don't use it, and don't link to it, as I tend to stick with established load data, which is never going to exceed the caes' maximum usable capacity!

Walkalong
January 9, 2007, 09:58 AM
Some people use water to give a comparison of different case capacities. Most wiegh their cases and sort them by wieght for accuracy purposes. Many benchresters sort cases to the 1/10 of a grain, but this is excessive for most purposes. For highpower they use a bigger variance for sorting, but you would need to post there to ask someone who shoots highpower. I have read articles about it but do not have experience there like I do with benchrest. I know folks in benchrest who use one lot of brass but do not wiegh at all. It is up to the individual how important it is. I sort cases for my benchrest rifle to plus or minus one tenth. I wiegh brass for my .222 mag heavy barrel varmint gun, but only throw out brass that is way out of norm for the lot. 5% or less culls I would guess. Ask the high power shooters what they do.

jmorris
January 9, 2007, 10:19 AM
I used a powder scale.
Brass is fired non-sized; number is water capacity in grains. I was trying to come up with a load for SSR and couldn't find any info on case volume. Measured some others while I was at it.

.380 11.9
9mm 13.8
38 super 16.5
38 TJ 17.3
45 GAP 18.7
.38 SPL 24.8
45ACP 27.3
.223 30.2
44 mag 38
50 BMG 294.9

USSR
January 9, 2007, 12:55 PM
Is there a simple yet accurate way of measuring a case's usefull capacity?

Yep.

Also, I heard that one should not use commercial reloading data intended for use in commercial brass when reloading military surplus brass or cases with thicker than usual walls beacuse of the diminished capacity of these which could lead to a dangerous increment in pressure, so finding out if the brass you will use is within normal commercial specs is also good for safety.

Yep.

I have read that you could weigh your cases and if they have different weights, but equall outside dimensions, then the heavier case would probably have thicker walls an consequently smaller capacity.

Yep (Hey, you're on a roll).;)

But what about filling cases with liquid and measuring the amount with a syringe? Could this work as well, and perhaps be more reliable? Are there other ways or is this just not critical enough to bother?

Blakenzy,

Here is what many of the members of Snipers Hide do: With the spent primer in the case, weigh the case. Next, fill the case with water from a syringe or something similar, being careful to fill to the top of the neck WITHOUT having the "dome" of water that a case will hold above the top of the neck. Now, weigh the case with the water in the case. Next, dump all the water out of the case, remove the spent primer, and weigh the deprimed case. The difference between the first two weighings is the water capacity of your case. The reason I like to weigh it the 3rd time (deprimed), is to be able to compare various other brands of brass, which typically is in a deprimed state. Note, with some military brass, such as .30-06, there is not a big difference in case weight and capacity from some commercial brass. However, in .308/7.62x51 there usually is. In any case, start low and work up, checking the velocity on your chrony and looking for pressure signs.

Don

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