I apologize for being a nerd on this, but I still do not see the physics on why S. Bell found that the 12/28 system had greater pressure (measured in the "same" place) than the 12/20 system. I do not believe that the minimal shot size difference would account for this.
I will not bother this topic again, since it can only reflect more clearly my stupidity--but I would greatly appreciate insight into the Sherman Bell measurement of the two 12ga systems.
Berrien
As 2-Piper pointed out, without initial pressure measurements of each load fired in a matching-gauge barrel, we do not know the pressure developed by each load under normal use. However, even though we can't really know, a likely explanation for your question could be that the 28 gauge load develops higher pressure than the 20 gauge load when each is fired in a proper gauge barrel. If you start with a higher pressure load to begin with, it's reasonable to find that it is still higher than the 20 when both are fired in a larger bore. Most handloaders know that it is hard to load a low-pressure 20 ga. load, and harder still to do it in 28. Note that there is no conclusion stated in the report from Bell about pressure whatsoever, and certainly not that the 12/28 combo is INHERENTLY higher pressure than the 12/20. It's just raw data that shows what happened with these particular two loads.
