I have never used any of the stuff, too rich for my bloodPlus I love my old Lefevers too much to risk it. I do recall seeing when it was introduced from several sources that it had a density of 12 gms/cc against 10.9 gms/cc for lead. This would make it heavier by 10%.
I did a google search for Hevi-Shot & from their own website all I could come up with was the density of "Hevi-Metal" shot. This is apparently a diferent mix than their original Hevi-Shot & it was stated to have a density of 10 gms/cc. This would make it about 7% "Lighter" than lead, but was given as 28% heavier than Steel shot @ 7.8 gms/cc.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra