Scott, Your test data seems to indicate 195#8's in a 24" circle at 45 yards to be in the realm of reality. Accounting for the differences in pellet count,chokes and yardage we're in the ball park.
Any 10 ga I've ever shot threw nice patterns,don't know if it's the extra payload or something inherent in the ballistics.
But you say you've got mouse holes in you patterns huh? I'd try mothballs in the shot hopper
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"Double guns are a sport and a pastime built into a beautiful package to which I attach myself when entering the great theater of autumn, those days now grow more precious because we are given so few".. Robin Lacy