nuggs,

If you would like some mind numbing tedium, or an idea for the punishment of naughty children, you could consider using a pellet head gauge :

https://pelletgage.com/

For informational purposes, I went through a few tins of JSB Express, and a few tins of JSB Exact, and found that there is a fair spread of head sizes within each tin, and there is a head-size that is the most common - for the above JSBs, nominally 4.52 mm, 75% were indeed 4.52 mm.

As the above tins were from the same dies (for each type), the information may or may not apply generally ! In addition, I reckon if I did the sorting again, I would probably get different results.

All said and done, I found the most useful aspect of the PelletGage, was that it let me cull the smallest and largest head sizes (4.48 mm, and 4.54 mm for the above nom. 4.52 mm JSBs). The smallest + largest, were, IIRC, around 2 - 3 % of the tin.

Have fun

Best regards

Russ