I sized two cases, trimmed to equal length and seated primers. I filled them both with water to the brim, as equal as the eye could make them.
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Here's the data
Scale is +/- 0.1gr, human error not measureable.

R-P .45 Colt empty = 107.7gr
R-P .45 Colt w/ H2O = 150.1
Total Water Wt = 42.4gr

Starline .45 Colt empty = 109.2
Starline .45 Colt w/ H2O= 151.2
Total Water Wt = 42.0gr

So the R-P Brass holds 0.4gr more water (Tolerance at least +/- 0.2gr).

What is the significance, for example, if I was using H110? Would there be a measureable increase in pressure/velocity?

Learning something new every day,
EMC2

I sized two cases, trimmed to equal length and seated primers. I filled them both with water to the brim, as equal as the eye could make them.
-
Here's the data
Scale is +/- 0.1gr, human error not measureable.

R-P .45 Colt empty = 107.7gr
R-P .45 Colt w/ H2O = 150.1
Total Water Wt = 42.4gr

Starline .45 Colt empty = 109.2
Starline .45 Colt w/ H2O= 151.2
Total Water Wt = 42.0gr

So the R-P Brass holds 0.4gr more water (Tolerance at least +/- 0.2gr).

What is the significance, for example, if I was using H110? Would there be a measureable increase in pressure/velocity?

Learning something new every day,
EMC2
That's less than one percent difference. It is probably even less considering case capacity under a seated bullet. I would think it is negligible. You can have that much variation within the same lot of the same cases.

It would appear you are measuring total case volume. When determining capacity you actually need to be filling the case to the base of the bullet, not the mouth. Since the bullet will take up aprox. 50% of the total case volume, you are actually dealing with about 1/2 the figures you derived. Either way, though, the difference will be, from your numbers, close to 1%. Typically thrown charges are very good if they will hold within this range. Regardless, a 1% difference in case capacity is actually insignificant.

To put this in perspective, with all other things equal a 1% change in loading density, either due to a difference in the charge or case capacity, will only result in aprox. 2% change in pressure for the load. With a 36,000 PSI load that is only 720 PSI difference. You will get much more than this in normal fluctuations round-to-round. A 3000PSI fluctuation under normal circumstances is relatively normal.

In other words, don't worry about it.

Agreed. Where the significance raises its head is in larger cases. I've seen rifle cases that vary almost 10% in water weight, by brand. Such a spread can really change performance, believe me!

But handgun cases? Nah, not so much.

First off, save yourself some trouble...if all you need are comparative numbers, can fill them with anything that is uniform, not easily compressed, and fine grained. Willg et a percentage comparsion that would serve your use fine. I generally used one of the very fine grained ball powders for this measurement...all i want to find out is that case A has 1.5% more volume than case B.

Same with worring about the depth of seating...would be seated to the same depth no matter what case brand, so the precentage of change would be the same no matter how the case's volume was measured.


Anything less than 2% is pretty well lost in the cluttter of other varaibles.

okay,
so what I've learned here is that a difference in case capacity of on or about 1% is well within the normal tolerance of pistol catridge loading and ignitions.

So, how about a .375 H&H case? Since one percent of capacity in those tubes means more, does that still hold true?

Also, what about a case's metal composition and it's maleability? I've noticed, for example, it's much easier to size and seat bullets in an RP case than it is for a Starline....?

The percent figure is still relevent in the large .375. I think Rocky's point was that rifle cases routinely see much bigger variations than you are measuring. For example, a Lake City .308 match case will weigh around 185 grains, while a Winchester will weigh about 155 grains. 70:30 brass is 8.3 times as dense as water, so this amounts to about 3.6 grains difference in water capacity, or around 3.3 grains difference in capacity for an average rifle powder.

One point: Cases stretch some under pressure, and it is the capacity of the case under pressure that determines peak pressure. So, measure the capacity of your fireformed cases to help deduce a pressure comparison, not your resized ones.