If we have two pistols of the same type same caliber, everything is the same EXCEPT the barrel length, is it possible to calculate the difference in the amount of powder one needs? For example, if a .40 pistol that has a 8 inch barrel that turns out to require 10g, does a 4 inch barrel sister pistol only requires 5g, while a 12" barrel requires 15g? Is the equation linear, or curve, assuming everything is the same? If everything is the same in the same situation, BUT a different twist rate, would that also affect the amount o powder needed? Is it possible to calculate or at this point it is a trial and error art form?