Jm - "mounted swing effort" is a measure of the muscle effort needed to to change the direction the gun is pointing. It is to mounted (from the shoulder) swing as weight is to lifting the gun (say from waist height to shoulder height). This gun requires little effort compared to heavy target or fowling guns which may require two to three times the effort. They are also two to three times as resistant to changing speed or direction.
Half Weight Radius is a measure of the gun's compactness. Typical guns are in the 10 to 11 inch range where this gun is down near 9 1/2" (compact). Guns above eleven typically have disproportinately heavy and long barrels and stocks while guns below ten tend to lighter and shorter barrels and stocks with proportinately heavier actions. This number is not as easy to understand, but once you get a feel for it, it gives you a useful snapshot of the gun's handling.
