safearm
US Veteran
While they shoot the same bullet and can generally be loaded to the same velocity, the big difference between the 9mm and the .38 Super is the case. The .38 Super has a straight wall case versus the tapered case of the 9mm. Because of concern of chambering a high power .38 Super load in older guns (.38 ACP), I believe the .38 Super was never loaded to its full potential. With hand loads, modern cases, and modern guns, you really can have a .357 Auto. Other than the versatility of shooting two rounds from the same breech size (.40 S&W and .357 SIG), I don't think there's much advantage of the .357 SIG over a properly loaded .38 Super.