How is the water capacity of a cartridge case
measured or calculated.
Do you just pour water into the case to the bottom of the neck then dump onto the power scale an weigh it.

Weigh a case, with a spent primer installed.
Fill the case with water, keeping the outside dry.
Weigh the water filled case.
Subtract the empty weight, from the full weight.

Adding a drop or 2 of dish soap to the water will reduce the surface tension and help reduce the munscis(sp) height (water bubble above the case mouth)

green

You fill the case to the top. Water weight is used as a way to compare internal capacities between different brands of cases and between different cartridges. The method you mentioned, filling to the base of the shoulder doesn't really tell you anything. If you want to use water capacity as input into a ballistic program you would measure to the base of the bullet seated to it's normal depth. Many ballistic programs use that as a starting point in determining powder charges.

Ray

quote:

Originally posted by greenjoy:
How is the water capacity of a cartridge case
measured or calculated.
Do you just pour water into the case to the bottom of the neck then dump onto the power scale an weigh it.

As a comparitive capacity measurement of one case to another this is the only way that has made any sense to me. the capacity of the neck is meaningless if it is filled with bullet. Actual case capacity availability is relative in rifle cartridges with regard to make of case, bullet used , magazine length and or throat depth.

There is no standard one number answer. roger

Greenjoy, I gave up using water to measure case capacity about 30 years ago, when I discovered that a case filled with ball powder will give a reading that is either the same or within .2 or .3 grains. This is certainly a lot easier and not as messy.

When using any new case I take two measurements with both a ball powder and a short cut extruded powder. One measurement is when filled to the top of the neck, and the other when filled approximately to the base of the neck which is usually the usable capacity.

The measurements with the two different powder types enable me to estimate more accurately which powder(s) is/are likely to give me close to a 100% loading density at maximum pressure. Brian.

Use ball powder instead. If all you are trying to do is get relative capacities, it works easier & is actually probably more accurate as it can be diff. to get all the water out. Fill the case full, scrape off the top & dump it in a scale pan. You can guestimate where the bottom of the neck is for usable capacity, but I'm not sure why unless you are planning a new wildcat?

If trying to determine the actual volume in CCs the water is a nice way to go. If you can get a close water weight in grains all you have to do is divide that number by 15.43 and you have the cubic centemeters. roger

Ball powder is the way to go. Small necks like the 17cals will leave voids even if you use a syringe. I use H380.