Alright, I have a question for everyone: I've heard people say that the LCP platform could obviously never handle the 9mm round. I disagree, but I'm not sure I fully understand the issue. Here's what I've learned:
The difference in length between 9mm and .380 is 1.8mm. In the overall length of the 2.75" barrel, I think this is negligible (same goes for the extra grip length that would be needed for 9x19 rounds instead of 9x17 rounds).
The difference in width at the base of the brass (because 9mm is tapered) is 0.43mm. In the overall width of the gun (0.82" = 20.82mm), this seems to be negligible.
The maximum chamber pressure rated by SAAMI for .380 is 21,500psi, whereas 9mm is rated at about 35,000psi. This is a significant difference, and results in a bullet with about 40% more kinetic energy out of the 9mm. Let's explore this, too:
It seems to me that dealing with more kinetic energy being imparted to the slide is just a matter of having stiffer springs, and a shooter who's willing to take the punishment of that energy on the tiny LCP grip. Fine - seems doable.
I also figured that maybe the chamber would need to be thicker to hold the pressure. However, the 9mm Kel Tec PF9 is only 0.88" wide - only 0.03" wider on each side of the chamber (if the extra width is in the chamber) than the LCP. This suggests that a 9mm can be made just as slim as the LCP.
So, can anyone tell me why the LCP couldn't be made in 9mm? It's not very obvious to me.