https://www.desmos.com/calculator/on4xzwtdwzIn the linked calculator, if you fix the ratio of cross-sectional area to mass and the distance traveled is always the same. So, it should be possible to calculate max distance given a certain release speed for a sphere or ellipsoid of any size.

Here, I assume a drag coefficient of 0.1 for the projectile and a spherical shape for simplicity (the Cd should probably be higher).

For a 65 m/s throw, the distance is 340m with a 50g stone and 390m with 50g of lead.

For Larry Bray's throw, the release speed I calculate using this method is ~75 m/s.

It is similar for a 500m throw with 50g of lead.

If you want to calculate it yourself:

For a 50g projectile the ratios are (the ratios change if the mass is changed because area and volume scale differently): this is in kg/m^2

Lead:154 (1.01cm radius)

Granite:59

Basalt:64

Approximately 41° is the optimal release angle with drag.

I included a quick calculator if you want to use your own size/material.