I see reference to measuring case capacity in cc's. Is this better than using grains? I believe grains would give a better/more accurate measure.

SchwarzStock wrote on Oct 10^th, 2024 at 3:33pm:


Liquid will give a more accurate capacity reading than grains. Grains may fill a case in different amounts each time you try depending on how the grains stack up inside the case, but water will always be the exact same reading.
I've tried filling cases with various powders to see how multiple cases of the same powder compare, and only very fine ball powders give extremely close capacities in multiple attempts with the same powder and same case. Flake and stick powders weren't even close to ball powders.

Basic science class time…

They give the volume of the case in CC or mL (same thing) because they are measurements of volume.  Other volumetric measurement examples are liters, gallons, fluid ounces, pints, quarts, etc.

Grains are a weight measurement just like grams, pounds, ounces, etc.  Grains are not an extension of individual granules of powder.

You can convert from a volume measurement to a weight measurement if you know the density of the item.  Water has a density of 1 gram per mL (assuming pure water at 25 C), so the conversion is very simple.

As for one unit of measure being more accurate than another?  As long as we aren’t confusing weight and volume, no unit of measure is more accurate than another, significant figures notwithstanding.  16 ounces and 0.00050 tons are both equal.  1000 g and 1 Kg are both equal.  7000 grains and 1 pound are both equal, and one measurement is no more accurate than the other.

Handloaders work in grain units because a 25 grain charge is less cumbersome to deal with than a 0.00357143 pound charge or a 1.61997 g charge.

Yes, case capacity is important for ballistics programs.  I use case capacity a lot with QuickLOAD when calculating loads for stuff where reloading data is non existent or sparse.  I just weigh the cases with and without a full load of water and calculate the volume.  It’s pretty easy since the number of grams of water is equal to the number of mL of water.

whene I messed around engines we used alcohol to messure chamber volume. water would have air pockets in the chamber somewhere.

A powder scale will measure .1 grain. .1 grain is .00647989gm. Who has a liquid measure accurate to .00647989cc? So weighing the water is more accurate than interpolating a cc measure especially since only a 1cc syringe is graduated in tenths. Just saying. (Sure, 1cc is close enough for programs.)

I recommend not drinking alcohol first.  Wait until after the measurements are finished 

The conversion from mass to volume with alcohol is a little bit more problematic than for water for people who didn’t pay attention in middle school math class.  Most alcohols, like isopropyl and ethyl alcohol, evaporate fast enough that you can watch the weight change on a balance capable of measuring to 0.1 grain.  That and there’s realistically no such thing as pure isopropyl or ethyl alcohol since they suck water out of the air, so your density will be off.  Top that off with the low surface tension, and the difficulties of reading a meniscus on a case filled with alcohol, and water becomes the better choice.   

Alcohol isn't cheap any more but, I still am so, I use distilled water for larger things, like cylinder heads.

I use distilled water because the weight of the gram, is based on what 1cc of water weights. What I do for cylinder heads, is use a 1/4" plexiglass plate, with a .080 fill hole and a .031 vent hole. I put a quantity of distilled water on a gram scale, squirt water into the plated head, with a hypo needle, until it reaches the vent hole, then subtract the difference and that gives me the number of cc/grams used to fill the combustion chamber, more accurately than reading the scale on a hypo syringe.

For cases, I just use my tap/well water to fill the case, measuring in grains, after I set the tare weight. The minerals in the water won't skew the results, enough to matter, for that.