Thanks. This may sound silly, but here's the reason for the question:
I'm waiting on delivery of one of the "Stainless Tumbling Media" kits, and the directions say to use five pounds of pins, one gallon of water, and two pounds of brass. I know those numbers aren't critical, but I like to be as close as I can on recipes if it's not too difficult.
My plan was to dump the pins in the tumbler, measure out a gallon of water, and pour it in the tumbler. Then I'd mark the water level on the inner tumbler liner with a scribe or some other permanent method. Then, I'd weigh out two pounds of brass and dump it in as well, marking the new water level.
Then in the future, all I'd have to do is put the pins in the tumbler, add water until the water level hits the lower scribe mark, and then add brass until the water level hits the higher scribe mark. Obviously, this would only work if the density of the brass was pretty much constant across calibers/brands.