GDU - balance and moment of inertia are different things. Balance is the point where the gun stays level teeter-totter fashion when placed across an edge or round fulcrum. I reference it to the (front trigger) as the best point to make direct comparisons from gun to gun; not the only reference point possible, but the best. Moment of inertia is a different attribute and I measure it with a small machine I have constructed.

Weight is a measure of effort to lift and hold. Balance is a measure of how the effort is divided between the two hands. Moment of inertia is a measure of the effort required to swing the gun.