Use this load. I think you’ll find great success. An oz of shot at 1250 is an oz of shot at 1250 regardless if it is spit out of a 20ga bore or a 28ga bore. Many 20ga loads will be sending that same oz of pellets the Winchester 28ga load does at the same speeds...
Which load though? The Winchester 1oz load of 5's or 6's is a VERY solid load. I typically shoot a handloaded 1oz 6's which very closely re-creates the Winchester load that is a HAMMER on pheasants. With the smaller capacity in a 28ga, I prefer 5's as the max size to keep the number of...