The formula that establishes the Incap Score for each caliber/round has been refined since the videos on the “Handgun Performance” page were made. The new formula accommodates real-world data that became available through Marshall’s later data releases (which I didn’t have originally). Notably, he had data for 40 S&W, which now allowed the formula to be based on an additional dataset. He also had additional data for the already included calibers (none of which changed more than about a half a point … a change that is down in the weeds for this kind of study). While the new data validated the basic approach, it led to a minor tweak in the formula. The chart below shows the new formula.
The online calculator uses the new formula. (In many cases, the change will be imperceptible; in the more significant cases, you’ll see a change of 1 point and, very rarely, potentially a change of 2 points.)
