Shot weight by Volume

If one is loading shot by 1 oz volume, is there a difference in weight between # 9 shot and #7.5 shot??

 

Yeah, there's a difference, but it's not night-and-day.

I've loaded enough shells by volume over the years that I've checked this myself with a scale. Same 1 oz dipper or bushing of #9 comes out a hair heavier than the same volume of #7.5. The little pellets just nestle in tighter with less wasted air space around them. You're talking a few percent at most maybe 10-20 grains depending on the exact lot and how hard the shot is, but it's real.

 

Yes, a 1 oz volume measure of #9 shot will typically weigh a little more than the same volume of #7.5 .