Originally posted by GlockBaby
Keep in mind the FBI slowed the 10mm down to 980 fps, so it would penetrate an average of 17.9". They wanted 18" of penetration, and, they got it.
The odd part about the 10mm is when you use the .40 bullets, at least the 180 GD's, 300 fps gives you maybe, a .5" more penetration, but, the bullet expands much better, up to .97 inches, vs the .6-.7" that the 40 usually opens up to.
Not all that odd. The bullets designed for use in .40 S&W are designed to "function" (open up) at much lower velocities than a 10mm is capable of. If they hold together at higher 10mm velocities and open to .97 that is a clear indication of good bullet design. And, yes, expansion like that at higher velocities is likely to reduce penetration because of the larger surface area from the larger diameter causing the bullet to slow down faster due to "media" resistance.