Hello,

I have developed load which my custom CZ-550 loves. Norma brass, 76gr of RL-17, GM215M primer, 300gr Swift A-Frame and 3.48" OAL. It is more consistent than Norma factory loads.

But it shoots at the same velocity (difference is not measurable in real world) from Federal brass like from Norma brass even if water capacity of Norma fired brass is 6.1g (94.14gr) and capacity of Federal (brass or nickel plated are the same) is 6.19g (95.52gr). (water capacity of SAX brass, made by RWS, is cca 6.05g).

My question is: Can this very small difference in water capacities make any real world diferences? Can it leads to dangerous pressures or so? What is the water capacity of another brass (Winchester, Remington)?

Just interested.

Jiri

Here is some food for thought.

Most powders are approximately the same specific gravity as water.

Brass is about 8X the specific gravity of water.

If you want to look at the volumetric difference inside the case as compared to the change in powder capacity divide the case weight difference by 8.

The answer for the difference in the Federal and Norma is NO.

If you weigh 100 of both cases you will have cases from each group that fall within the distribution of the other group.
Only a few cases at the extreme of each distribution will not fall in the distribution of the other brand.

quote:

My question is: Can this very small difference in water capacities make any real world diferences? Can it leads to dangerous pressures or so? What is the water capacity of another brass (Winchester, Remington)?

The difference in case capacity would only make a significant pressure difference if you were at the absolute upper limit of pressure with your loads. So in real world situations the answer IMO is no.
That being said, I don't mix cases from different manufacturers (or lots) without working up loads. Brass is cheap.

Unless the capacity is measured after the brass has been fired in the same chamber then it is somewhat meaningless.

The difference in capacity of two different brands of unfired brass may be due to its being closer or further from minimum and maximum dimension as it comes from the factory.

A case with dimensions near minimum which measures 90X before firing might have a capacity of 95X after firing, whereas a case of a different make with factory dimensions near maximum with an unfired capacity of 93X might have a capacity of only 94X after firing.

Bottom line: You will only know how much of the chamber space the case takes up once it is fired and takes on the shape of the actual pressure vessel (the chamber).

Stonecreek:

All capacities I measured was after firing in my rifle. I understand that comparing to fired case in different rifle is meaningless.

All: That is exactly what I thought (that difference is negligible. Thank you all for your opinions.

Jiri

Can it?-Yes
Also the shape of the Flash Hole in the brass can play a factor.
How strong the brass is, ie,how well it holds the bullet into the neck.

375 brass seems to vary between makers; I load them all the same, BUT shoot only like cases together. Best to have only one make. But I have not noticed any difference but I mostly shoot at 100 yards.