@omega21 Kinetic impulse (change of momentum) is easy ( https://en.wikipedia.org/wiki/Impulse_(physics) ). In our case initial momentum is 0 in our plane of reference. For our use it is same as "Power Factor" in IPSC/USPSA or IDPA. It is V0 velocity in meters per second multiplied by bulleg mass in kilograms. Impulse 3.1 for 115gr (7.5g) bullet means V0 of 413m/s (1355frps). This means PF 155,825 (divided by 1000 for IPSC/USPSA). When you put 124gr you will get that it will be 1257fps ammo to get this factor. For SFP9 2.6 impulse means Power Factor 130,691. Still hot enough.