While browsing the net yesterday, I came across the .32 NAA round. It was advertised as having over 1200 fps velocity. At first I thought that was pretty cool. The .32 ACP only does about 1000 fps, and the .380 does a little less than 1000 fps. Then it hit me. If you neck down a case to fit a smaller bullet, you are still limited by the maximum pressure for the case. That means that essentially the kinetic energy of both rounds will be the same. The round with the smaller bullet will go faster, but has less mass. I looked this up for the .380 and .32 NAA. The .380 has a KE =200 ft-lb. The .32 NAA KE = 199 ft-lb. This provides no benefit in stopping power, although you will get a flatter trajectory. At mouse gun ranges, though, I doubt it would matter much Other rounds such as the .22 TCM and .357 Sig are a little misleading, though. Although sometimes listed as such, the parent cases of these rounds are not the 9x19 and .40 S&W. The .22 TCM parent case is actually the 5.56 NATO, and the .357 Sig is longer and thicker than the .40. More likely it was based on the 10 mm. As such they are capable of higher pressures giving potentially more kinetic energy than the 9 mm and .40 S&W. Interestingly, though, while the .357 sig has more energy than the .40, the .22 TCM is actually loaded similarly to the 9mm actually producing less kinetic energy than the 9mm. Probably since it was designed to be used on 9mm frames.