measuring water capacity

[sailorjim]

I have heard two schools of thought on this.
1. Measure fired cases as this is the capacity within the chamber.
2. Measure sized cases because when it is time to stuff powder and bullet, this is what you have to work with.
Which procedure is correct and why?

 

[357Mag]

I have heard two schools of thought on this.
1. Measure fired cases as this is the capacity within the chamber.
2. Measure sized cases because when it is time to stuff powder and bullet, this is what you have to work with.
Which procedure is correct and why?

Sailorjim -

Howdy !

Use a fired case, when you have one. You can then use individual powder density to calculate what the max charge night be ( capacity-wise.... not safe pressure-wise ).

That way... you'll know fer sher that in no instance, would you ever exceed this amount.

There's some info on this included in the usage directions for the on-line " Powley Computer ". kwk.us/powley.html


With regards,
357Mag

 

[FEENIX]

I have heard two schools of thought on this.
1. Measure fired cases as this is the capacity within the chamber.
2. Measure sized cases because when it is time to stuff powder and bullet, this is what you have to work with.
Which procedure is correct and why?

To find the H20 capacity only, I do both. The actual safe powder capacity is another story.

 

[sailorjim]

Thank you both for your replies and I appreciate the Powley Computer reference.

 

[Stammster]

Fired case capacity gives you the internal volume of that brass fired in your chamber.

Case capacity after resizing gives you internal volume of that brass for your die.

Depending on the size of your rifle chamber and dies, the volume after FL resizing could change (reduced) by as much at 0.5-1.5 gr H20, assuming you only bump the shoulder back a few 1000s. Neck sizing is a lot closer, but there is still a slight difference.
(Note: I measure case capacity in grains H20 using my scale. Note case trim length also, as that also effects capacity.

The question is, what are you going to use that H20 capacity number for? If using it for QL, I would use fired/not resized. However, as long as you are consistent and measure your velocities - either method will work. You will just have a slightly different Ba for your lot of powder depending on method, in order to get a match of MV vs powder charge weight.

 

[Mikecr]

If grouping cases matching in H20cap then you need to fully fire form(several firings), trim, measure &, separate.
If you neck size only, you're done. You have your static capacity.
If you FL size cases then you'll also need to measure H20cap of static matched -after sizing/retrimming.
You'll throw out more offenders there. This is dynamic capacity.

Some try to save efforts here by weighing cases first. I wouldn't throw away any cases based on this alone except for very big departures.
I also wouldn't keep cases based on this alone, so I personally see little value in case weight measurement.