The explanations from Ken and Rocketman are spot on in my opinion.
I have several guns that I shoot particularly well, but all are different. One is a 12g 682 gold E, 32" bbls, 7 3/4 lbs, very muzzle favored (but not muzzle "heavy"). Another is a 20g Browning 525, 32" bbls, 7 lbs even, very muzzle favored. The last is a Browning BSS 20g, 28", 6 1/2 lbs, slightly muzzle favored. I've shot well above other guns with these, almost astonishingly so, to me at least.
There's something about these guns that I need to quantify. Rocketman's rig for deriving MOI is the only method I've seen to do this.
