Raimey, I looked it up and the number is actually 96: A shotgun should weigh 96 times the weight of the shot charge to avoid excessive recoil. But a couple of factors may mitigate the rule in different directions. The rule of 96 dates to the days of black powder, and because modern smokeless powders tend to produce greater velocity, a 6-pound gun (96 ounces) shooting one ounce of shot will kick harder with modern loads than with black powder. On the other hand, the intended use back then was high volume driven shooting, and the loader likely carried the gun to the peg for the "gun." If the intended use is flushing upland game, a little more recoil may seem a fair trade-off for reduced weight as the gun is carried a lot and shot a little.
