Water weighting cases

[RJinTexas]

When inputting info to develope loads on QL for a wildcat cartridge you must know the water volume. The good folks at QL told me to simply use vasoline to plug the primmers hole on a fire formed case. I was told to average 4 fills two with the water concaved and two convixed, divide by 4 and input that for the volume. That what I did for my 20VT load development.

RJ

 

[langenc]

So much technicality!!

Just to muck it up-if I remember 1cc does NOT equal 1 ml--close but not exact.

 

[jlow]

Yes, thanks! I did miss spoke, what I wanted to say when I said 1 ml of water = 1cc of volume was I mL of water = 1 gram in weight…. Alzeheimer must have been strong that day! :

Even though we are looking for volume difference of the cases, the reality is the absolute volume translation is not important, it is the relative difference in either volume or weight of the measuring material between the cases that you are interested in. Those relative numbers will allow you to bin the cases according to volume.

That is why you can use rubbing alcohol or ball powder both of which of does not even have the same density as water. As long as the density of the material you are measuring with remains unchanged for each case, then the relative weight of what you are using to measure the case will reflect relative volume. Here the caveat for water are bubbles inside the case, or uneven packing for ball powder. Rubbing alcohol is probably the best as there is less chance of having bubbles and of course density is not an issue.

 

[mikecr]

You can add a few drops of alcohol to the water & touch with a tissue corner to flatten meniscus.
I am surprised about y'all getting consistent volumes with FL sized cases. Either my standards are higher or my cases have not been as good. Dimensionally my cases are perfect as measurable when I test, and it takes very little variance to hose capacity.
I use either Lapua, Norma, or Winchestor.
I have seen plenty of mis-correlation in weight -vs- volume, and this is the only reason I measure capacity.

There is another factor in the affects of capacity variances: Load pressure
If running very high pressure loads(beyond SAAMI) then you're looking at a work-around for many things, including load density/capacity. Hence the popularity of extreme pressure loads. But nothing is free, and larger hunting capacity cartridges cannot utilize this work-around.

 

[jlow]

The fact is the correct answer is likely “it depends”. I had great luck correlating weight to volume for 223 LC09 brass but less so for 308 Win brass. The fact that you are running very high pressure may mean that you are consistently pushing the case out to chamber dimensions and so less affected by some of the variables I mentioned.

So in the end, it comes down to if anyone is interested in doing any of these techniques you have to “trust but verify” LOL! In this particular case (pun intended), there are just so many ways that your situation can be different than the next guy so unless you go there and test your stuff with your best technique, you are never going to be sure that your technique is good enough and/or whether it means anything in your particular situation. Going blind and following the "other guy" will usually get you in trouble.

 

[mikecr]

You just won't know unless you measure.
Sometimes I get a lot of brass where weights trend as expected, with a few outliers.
Other times, nothing is predictable, and that's when I'm glad to be checking.

Another thing I found is that between case brands mentioned, and depending on cartridge, and depending on lot, there is no way to declare one brand better than another -up front. And this follows thickness variance as well.
It just has to be measured(not assumed).

As far as it taking a lot of time & effort, and whether worth it?
I know only for for midsize cartridges, running rational pressures, in the best guns I can have built, it's been worth it.
When nothing else, I can atleast rule out my ammo as a factor.

 

[jlow]

Yea, anytime you start assuming or using something somebody else found you are heading for trouble.

As for time and effort, I’m with mikecr. The way I always think about precision reloading/shooting is there is just so much in it that you don’t know about or control that if you don’t even bother to measure and control the stuff you can do, you are just heading for a disappointment.

 

[Phil3]

to 21shooter -

A well designed and Innovated idea'rrr !!!

Thanks for coming up with it and marketing them. I will be ordering a pair from you to do my spent case capacity. Should work much better then my modeling clay method....
Donovan Moran

I made one, but had not yet cut the groove for the O-ring. But, after learning about value of water capacity, I think I will have to complete the thing so I do can the water weight.