Plated bullets may work okay in some instances, but try regular cast bullets of the right diameter for comparsion. Try several different such bullets if available. Refer to a Lyman book; lots of cast loads. You might speed up some of your non-max loads a bit; many of those are too slow and that can be one of many factors that affects accuracy.

Work toward an accurate load first; consider extreme spread next if you consider it at all. Extreme spread and standard deviation indicate consistency only and not accuracy. Many loads with low numbers will not be accurate. Many more factors make up accuracy. That's not to say you can't have an accurate load that has low numbers, because you can, but striving for low numbers first is not the best way to go about this.

It's good you're testing loads at 25 yards. This will save much time and ammo during load development as you can quickly weed out bad loads, something that's difficult to do if you test up close.