Hi John,

You might try

bucket size of 48

Shate Rate 0.05

Filter to Sinc filter 3

Lower your raytrace bounces to 1

1 for image in the chrome ball

2 for a chrome ball in another chrome ball

3 for a chrome ball refecting a chrome ball in another chrome ball and on and on

Pixel samples to 12 or even higher  (type in)

and maybe even try with enable Inderiect Light unchecked as a second attempt

Just my 2 cents worth

Tom