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Theoretically, the RG could be any distance from just over 0 inches--by placing ultra-dense materials in the center of the ball and extremely lightweight filler beyond--to just under 4.2975 inches by placing ultra-dense materials near the outer shell and filling the inner areas of the ball with lightweight foam.
In the first example, the ball would be as center heavy as possible. In the second, it would be as shell heavy as possible. The problem with unlimited RG is that the two extremes would produce variations in ball performance that would be enormous. One would roll immediately and the other would "lope" all the way through the pin deck.
The ABC/WIBC, in an attempt to limit the amount of variation in ball performance that could be achieved through construction, placed minimums and maximums on RG. The rule states that the minimum RG can be no lower than 2.430 inches and no greater than 2.800 inches. This means that every ball must act as if its entire weight (mass) is rotating at a distance of not less than 2.430 inches or more than 2.800 inches from the axis. Since the total span of RGs ranges from 0 to 4.2975 inches, technically all bowling balls fall within the overall medium RG range. However, when anyone in bowling talks about RG, they are not referring to the total range of possible RGs, but instead only to the RG range allowed for the sport--2.430 to 2.800.

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