Gryffin is right. The speed of sound figure people are used to seeing is the speed of sound in air. Here's a table with figures in mps, not fps, but you get the point.
State Substance Speed in m/s Solids Aluminum 6420 Nickel 6040 Steel 5960 Iron 5950 Brass 4700 Glass 3980 Liquid Sea Water 1531 Distilled Water 1498 Ethanol 1207 Methanol 1103 Gases Hydrogen 1284 Helium 965 Air 346 Oxygen 316 Sulphur Dioxide 213
And Gryffin's previous post is spot on about energy figures and stretching and ballistic effect. We've all stretched a rubber band, and then stretched it again to the point that it broke. Handgun bullets generally stretch the tissue a lot, but it can spring back. Rifle velocities produce stretching that exceeds the tissue's ability to spring back. This is a big part of why talking about muzzle energy or 100 yard energy or what have you in rifle rounds, and then extrapolating down to handgun ballistics like there's no real non-linear difference isn't smart. For rifle rounds, I want to know energy. For handgun rounds, I want to know momentum.
Was there math in that? If so, pretend you saw a disclaimer.