Originally Posted by vandros
So, this only affects hardcast bullets? Is faster = more penetration with FMJs?
It's pretty much true across the board. Hardcast, FMJ but especially JHP bullets. One of the downfalls with loading bullets warm, no matter the caliber is that when you push them beyond the velocity they're designed for, it's going to negatively affect performance.
A positive example would be 9mm bullets designed for the 9X19 and others designed for the faster velocities of the 357 Sig. Also some .357" JHP bullets are designed for 38 Special velocities or low-end .357 Mag, and then there are .357" JHP bullets designed specifically for full house .357 Magnum speed. Same with 44 Special vs. 44 Magnum and .45 Colt vs. "heavy" .45 Colt/454 Casull.
A negative example would be most all .400" JHP bullets as they're designed for typical .40 S&W velocity. When you load the .40 S&W warm, or the 10mm too, you begin to push bullets beyond what they're designed for and that can limit penetration. Now as you begin to push them faster you may gain penetration and expansion up to a point, but after that is reached, you will begin to lose penetration although expansion may increase or worse, the bullet comes apart. Like I said, some .400" JHP do better than others at higher speeds.
Same is true with loading the .45 Super/460 Rowland with .45 ACP designed JHP's. I've found that some .45 ACP JHP's don't like to be pushed much more than 1200 fps, but others can handle a little more. Some .45 Colt JHP designs can be loaded in the .45 Super/460 Rowland, but sometimes their profile makes them a poor choice for feeding. Although there are some 240-260gr designs that will work, but after that you've got 300 grainers and they're too heavy for either to shoot fast enough.
As for hardcasts, what Tiro Fijo said is right on "Hardcast bullets in a handgun are not as dependent upon velocity to fulfill their mission."