If you want a "4" in the caliber

You should just make it a 45 ACP

"Police departments around the country are finding that the .40 calibers aren't as effective if an unfortunate incident occurs and they're forced to have to use their weapons," Rutherford said. "[The larger caliber] is safer for the deputies and for the public if the unthinkable happens and we have to do what no one wants to have to do."


The .45 ACP automatic pistol cartridge has been considered one of the best defensive handgun rounds for the past 100 years.

Seems its hard to improve on things John M Browning designed