Pattern for leather light infantry helmet?

[Colmoultrie]

Does anyone have a pattern for the leather light infantry caps from the F&I or AWI?  I've thought of taking apart a ball cap and using that as the basis, but if someone has an actual pattern, that would be better.  Any suggestions for leather weight? I was thinking about 4 oz.

On another level, I know that jacked leather is boiled, but would I do that before or after I sew the pieces?  Does boiling leather shrink it, and if so, any guide for how much?

Thanks!