I found some test slugs of ERS left over from the 2016 alloy shootout. After aging 10 months, it scored 34.2 BHN (10mm / 149 kg). That compares to 32.6 BHN for straight J.R. brand reclaimed shot that aged 10 months, or a 1.6 BHN increase.
It appears that, in general, my ERS recipe increases hardness 1.6 - 2.0 BHN compared to straight J.R. brand reclaimed shot. Individual tests are sometimes as high as 45 BHN but that may be due to measurement noise because if you do a lot of tests, the average is less than 45 BHN.
My DERS recipe appears to increase hardness 3.0 BHN, if even that, compared to straight J.R. brand reclaimed shot.
Those are small improvements that could easily be explained by the higher antimony content.
Just to be sure, I'll eventually test J.R. shot plus sulfur. My guess is that the sulfur will not increase hardness because shot already has an adequate amount of catalyst.
It seems that reclaimed shot is already close to optimal for heat treating. If there is some modification or trick that can substantially increase its hardness, I have not found it.
By the way, for measuring hard alloys I have settled on the following technique with the 10mm / 149 kg test. I measure across the indentation vertically, horizontally, and at 45 degrees, and take the average of those 3 measurements. The 3 measurements are rarely exactly the same because sometimes the edges of the indentation are rough, or sometimes the indentation is slightly oval.
Taking the average smooths out those errors.
For softer alloys, this method may be overkill.