The attack tables are what RM is known for, however, I wonder if there is a more realistic way to arrange damage? For instance, would it make more sense to first assign the area being hit (with roughly humanoid, quadroped, octoped etc anatomies) then determine the damage and critical? If the assumption is that a given armor type protects better and lessens damage and criticals, yet if the critical indicates an area not covered by armor it doesn't really make sense. So for instance, the first roll would be the area hit. For humanoid, chest area would be about 40%, legs 15% each, arms 10% each (or 20% for one arm if a shield is used) and head 10%. Then you would roll the damage and critical based on the armor type, so a leg shot with breast plate would be AT 1.
You could even adjust it for more realism so that say a quadroped would not a lower chance of a head strike against a humanoid etc.