that take into account gun weight? It might be closer if real world weights are used. (of course we don't know what a Barrett Fieldcraft in a magnum caliber would weight) but the different in Kimber Montanas from a 7-08 to a 270WSM is 17 ounces. (5#,2 oz to 6#, 3oz)
20% increase in weight might make a 20% decrease in free recoil... probably brings ya'lls calculations alot closer together.