12 gauge light loads

[Cold Spring]

This thread seems to be off on a tangent. The OP asked about light loads < 9000 psi and it seems most of the replies focused on lighter than standard payloads for the respective gauges, i.e., 1/2, 3/4 and 7/8 ounce in 12 gauge, etc. I understand that often means lower pressure but not necessarily so; it would be helpful if the replies stated the payload mass (weight) and pressure as tested or as shown in a published reference.

Also can anyone explain the ballistics ..... why it is that these lighter payloads are often quoted as target crushers, seemingly and enticingly more so than a heavier standard payload in that same shotgun/choke and with the same hold on the target?