Home Forums Hunting & Shooting Ask The Gunwriters Calculating Total Rifle Case Volume

I was wondering how you calculate total case volume? I have read references to this in terms of water?? How can the do-it-yourself'er figure this out themselves?

For anyone who has read my other posting "Headspacing Show & Tell" I am doing some additional fact-finding and wanted to see what the volume increase was on my alleged 9x57 Mauser round factory vs. fireformed seen below.

http://www.runcss.com/MAI/capacity.jpg

Thank you

I think you'd weigh an empty case, record the weight, then fill it with water and weigh it again. That's the volume in grains.

Yep.

I usually do it with a bullet seated to its normal depth, which gives a better idea of useable volume.

1) Weight an empty, fired case with the spent primer.

2) Fill the case with water.

3) Stand the case next to a loaded round, then insert a bullet into the neck of the water-filled case until the bullet is at the same depth as that of the loaded round.

4) Carefully pull out the inserted bullet, wiping any tny drops of water into the case neck. Wipe off the outside of the case and weight it. (Surface tension will keep the water inside the case.

5) The difference between the weight of the empty case and the same case filled with water is the amount of functional powder space.

Or weigh the bullet + case and you don't have to pull the bullet.

That would sure work, but one problem is that some cases + water + bullet exceed the capacity of many reloading scales. There is also the problem of the sheer weight of the bullet continuing to squeeze water out of the case as it's handled.

MD Is there a chart of the volumes of various cases

Not MD, but here's a web site with a list of capacities of some cases. Helpfully, some sources are provided.

http://kwk.us/cases.html

Apply usual number of grains of salt.

--Bob

Unfortunately, those are capacities full to the case mouth. Capacities with a bullet seated are much more useful.

Ken Water's published a chart of case capacities to the base of the neck in an old HANDLOADER'S DIGEST, I believe the 8th edition. I used those for a number of years, but finally decided it was more accurate to do the job myself, due to differences in brass and bullets.

For Quickload, is it more accurate to use usable volume or total volume? Not trying to start a debate about QL, just curious if one is better than the other.

My old LOAD FROM A DISC program gives case volume as both grains of water and something else symbolized as: (in^3), I understand grains of water but not (in^3). For example; they list case capacity of a 300 WSM as 78.656 gr. of water and
(in^3) as 0.312. So which is better? Or if I'm happy with grains of water should I even care about the other spec.?

Useable volume is better.

Unfortunately, capacities with a bullet seated vary with bullet style, chamber throat, and magazine length (ie. seating depth). Since it's fairly straight forward to calculate the displacement of the seated bullet, all internal ballistics programs start with the capacity of the empty case, and the list in question was written for use with a Powley Computer.


For internal ballistics calculations, one needs the net (useable) case capacity. QuickLoad has a large database of bullet dimensions and will accurately compute the net capacity if you give it the case and cartridge lengths. If you've measured the net case capacity instead, you twiddle the seating depth in the software until you match your net capacity. Both ways give the same result (when the bullet dimensions are correct).

As for grains of water, there are 252.4 gn of water per cubic inch.