update: k, so I started recording today, but after a minute or so I realized today is magic crit dmg stones..
I didn't account for the fact that 8 physical crit dmg stones only appear once every two weeks.
I could do 500 rolls for magic crit stones too, but I'd rather keep the consistency. To get a rate that's close to the true one, it needs at least 1000 rolls especially with smaller chances. There should be a way to calculate the confidence interval of 500 vs 1000 rolls, but I still need to work it out.