Playing around recently and had some results that seemed better than I remembered so I dug out some of my old shot loads that used #9 shot.
Speer .38 capsules hold:
100.9 gn #9 shot /.8 gn per pellet = 126 pellets
106.9 gn #12 shot/.2 gn per pellet = 535 pellets
Speer .45 capsules hold:
154.4 gn #9 shot = 193 pellets
166.7 gn #12 shot = 834 pellets
I guess I never sat down and did the math when I switched over to #12 shot, makes a fairly substantial difference.
So despite my .380 ACP shot loads only having 61.6 grains of #12 shot in them they patterned better than my old 38spl #9 loads because while the payload is less there are 182 more pellets being sent down range (308 vs 126).