Feedback on how too figure out Case Volume

[El Sancho]

Gentlemen,

I'm trying too figure out the correct way to find my case volume on each case 300 SAUM. This is the way I'm currently doing it. So plz let me know if I'm correct.
Example: case wt with water 298.1grs
Minus clay plug- 1.5 grs
Minus empty case wt 223.1grs
Total 73.5 grs of water
Respectfully
Manny Sanchez

 

[Bbear]

Mine is similar
Using a fired case (2x at least) and leaving the fired primer in
weigh empty case
fill level to case mouth
weigh case with H20 in it
subtract empty case weight from case w/ water = capacity of water

Repeat for 9 or so more cases to get an average.

Note, cases should be the same brand, lot etc unless you are looking to see which brand holds more in your rifle.

 

[Ned Ludd]

Leave a spent primer in the case, or put a used primer in backwards (flat side inward). Zero the balance with the empty case first, then fill with water and re-weigh. Typically, using a density for water of 1 gram per cubic centimeter will be sufficient, although you can find temperature-specific density information that goes out to several decimal places if you really think it's necessary.

http://forum.accurateshooter.com/threads/case-volume-determination-pic-heavy.3896148/

 

[David Christian]

Would love to see some empirical data on measuring case volumes and their results on target or ES/SD. Anyone seen some good results?

 

[Keith Glasscock]

I'd love to see repeatable results measuring case volumes with liquids.

 

[T-shooter]

A nice case plug is the 21st Century piece. It seals with an o-ring. I bit of case lube on the 0-ring makes it easier to use. I fill the case until it has a slight crown and then wick off a little with the edge of a paper towel until it is flat across the neck.

http://www.xxicsi.com/primer-pocket-plugs.html

 

[Straightshooter1]

First, I make sure the cases are all trimmed to the same length. Then, I insert a spent primer upside down into the primer pocket. After sitting the case on an electronic scale, I zero the scale and fill the case with H20 with a small squeeze bottle. Like above, I fill the case until the surface tension it's slightly above the mouth. To get it level I use a paper towel to wick on enough until it is level with the mouth. In order to see this easily, I use a bright light source that reflects of the surface so I can tell when it's actually level. This is when I record the readings on the electronic scale. I've double checked this to see what kind of variance in weight there might be and found the measurement quite accurate/repeatable. Every time I go on to a new case to weight, I zero the scale for the new case each time so that the variances in case weights are not a factor.

 

[dmoran]

In my experience, the cases should be fired at least 2-times in the intended chamber (takes at least 2 before the brass settles in / down).
Freshly sized (to a uniform bump number) and trimmed equally.
At which point the cases will be as equal as there going to be.

My 2-Cents

 

[Keith Glasscock]

First, I make sure the cases are all trimmed to the same length. Then, I insert a spent primer upside down into the primer pocket. After sitting the case on an electronic scale, I zero the scale and fill the case with CO2 with a small squeeze bottle. Like above, I fill the case until the surface tension it's slightly above the mouth. To get it level I use a paper towel to wick on enough until it is level with the mouth. In order to see this easily, I use a bright light source that reflects of the surface so I can tell when it's actually level. This is when I record the readings on the electronic scale. I've double checked this to see what kind of variance in weight there might be and found the measurement quite accurate/repeatable. Every time I go on to a new case to weight, I zero the scale each time so that the variances in case weights are not a factor.

Carbon dioxide eh?

 

[Ned Ludd]

Carbon dioxide eh?

Well, CO2 is more dense than air.

As far as reproducibility, read my case water determination report at the link I posted a few responses above. Near the bottom, I show the avg. +/- SD for water weight determined for the same case 10 successive times. I do measurements like this routinely. With a little care and practice it is not difficult to obtain accurate and reliable water measurements in fired cases. IMO - the two keys are shaking down the case sufficiently to remove any bubbles, and using a backlight to ensure the meniscus is perfectly flat.

 

[jepp2]

IMO - the two keys are shaking down the case sufficiently to remove any bubbles, and using a backlight to ensure the meniscus is perfectly flat.

Read your report. Very interesting. I routinely measure case volume for QuickLoad calculations (so I do so on fired cased that haven't been sized). My scale isn't up to yours on accuracy, but does what I need. Totally agree on having a flat meniscus. But I never even thought about filling the case by dipping it. I use a syringe with a curved plastic tip that comes to a small diameter. I just run a small stream of water down the inside of the case neck. I also add a couple of drops of Dawn to the water. I have no trouble being repeatable within 0.1 grain.

 

[Straightshooter1]

Carbon dioxide eh?

LOL!!! Nope.

I guess global warming was on my mind . . .???

 

[El Sancho]

Thank You Gentlemen on your feedback..

 

[Metal God]

I'd love to see repeatable results measuring case volumes with liquids.

I measured case volume of some308 LC-12-LR and LC-10 cases several years ago . I then ran the test again using the same lot of cases but likely different cases from the lot a few years later . The reason I did it again was to see is fire formed cases had the same constancies as FL sized case . These were done with 10 random pulled cased pulled from a 250ct lot each time . My average case volume only differed by .2gr in both head stamps likely meaning they were closer to the same and I just did something slightly different the second time . Either way .2gr in a 308 case is nothing and would likely get lost in the noise of reloading a case .

I have all the data somewhere If I find it while I'm still thinking about it I'll post those results .

 

[mchees1]

A nice case plug is the 21st Century piece. It seals with an o-ring. I bit of case lube on the 0-ring makes it easier to use. I fill the case until it has a slight crown and then wick off a little with the edge of a paper towel until it is flat across the neck.

http://www.xxicsi.com/primer-pocket-plugs.html
View attachment 1115128

I use these case plugs too and like the ease of use to test multiple cases - worth every penny. Totally agree with T-shooter: lube is necessary to not tear the o=ring and increase longevity. Wicking with paper towel works perfectly to get accurate and repeatable results.

 

[El Sancho]

Thanks Again Gentlemen...I do plan too order those 21st Century.
Manny

 

[Uncle Ed]

Quickload tells you to measure case capacity using fired cases that conform to your chamber. The smaller the case the more it effects the chamber pressure.

Case volume effects chamber pressure and velocity, example below.

Using Quickload and the chart below the top Lake City case at 30.6 and the bottom "old Lapua" case at 28.0 will change the chamber pressure 6,000 psi with the same charge of 25.0 grains of H335.

NOTE, Quickload defaults to the smallest case capacity that can greatly effect the pressure and velocity readings. This is why you need a chronograph and change the burn rate to calibrate Quickload to get more accurate velocity and pressure estimates.

Again, larger capacity cases are effected less by case volume.