May I suggest a little standardization of ammo?

The air dry clay is inexpensive, uniform, and relatively simple to form using the CA roller method (I swear he didn’t pay me to say that )
I think we should choose some reasonable dimensions for ammo in roughly 10g increments so we can all be slinging very similar projectiles when we want to be consistent across the globe.

Of course there’s nothing wrong with the other ammos  woodsj suggests, but when we need consistency for data collection purposes, my vote is for “standard clay”

Well, that's definitely a problem for highly-accurate testing. It's the difference between a jacketed lead Spitzer-point boat-tailed bullet, and an unjacketed hollow-point wad-cutter made out of aluminum. To get a really good comparison, we'd need to make uniform ammo, of the same density, balance, and shape, which would require machining a mold and casting our own and weighing them for uniformity and so on... That will need to wait until we can get a smaller sample of highly-skilled slingers together for comprehensive tests.

But for our purposes, looking at a slightly less scientific/engineering and more historical/humanities side, there's some lee-way.

Uniformity is already provided with the sports equipment elements, so that solves a problem there. For the other ammunition types, we'll at least be able to see some patterns, and see what would be worth studying in future. For example, Rough/Irregular rocks are already known to be less than ideal, but seeing if there's a difference at all between smooth and rough egg-shaped stones might be interesting. Same with egg vs round metal shot. Perhaps for the majority of us, any reasonable metal ammunition will be basically match-grade at the ranges we sling for...

We'll see, once the data gets collected...

Bill Skinner wrote on May 18^th, 2018 at 5:02pm:

Hey, I once invented a recipe for calibrated mud and had a test method and test apparatus to verify that the mud was within spec. You’ll have to try harder than that to monkey up our plans 

I make pottery. 

Clays are way different, even in the areas where I get mine.  A lot of that will depend on how much organic material is in it and the other is how much silt is in it.

We won't even go into the differences between the types of clay such as Terra Cotta or Kaolin.

Usually, commercial clays are Kaolin but not all. 

And the air dried with plasticizeirs will be lighter than a similar clay without that is to be fired in a kiln.

May I suggest ball bearings, specifically some form of roller bearings? 

They are steel, which isn't as harmful to the countryside as lead, they are uniform and they have a polished surface.  Not quite the correct shape but close.

Any kitchen scale should be reasonably accurate, and to get the volume you just drop a known mass of clay into a measuring cup half full of water. However much the water rises is the clay’s volume. Divide the volume by the dry weight to get the ammo density (this assumes negligible shrinking as the clay dries).

So, it's now occurring to me that Glandes in the classic almond or biconical shape aren't just so you don't have to load them more carefully... They're like Boat-Tail bullets.

I should have caught that sooner.