One of the things that irks me a bit is that some 9mm fans today think the 9mm was always what it is now, and don't understand how anyone could choose something else. They never knew the time when 9mms were ALL single stack mag guns (with the exception of the Browning Hi Power). They may know, but I don't think they realize that there was the 9mm, then the 9mm +p, and now 9mm+P+, and how, if the round had been adequate to begin with, the hi pressure versions wouldn't have come about.
Yes. Well, to expand on this a bit.
The whole +P thing became a thing due to expanding bullets, really. Not just in 9mm, but also for other calibers. Let's turn the wheel of history a bit back.
I mean, take the late 19th and early 20th century rounds. They're generally much more modest then modern ones ballistically. As long as you're not spending bullet energy to deform the bullet itself, something like 650-700 fps and 200-220 grains, around a modest 200-ish fpe, is entirely suficient to penetrate sufficiently - around 18"-20" of ballistic gellatin. Many rounds of the period were rather modest (.44 and .45 Webley, .44 Colt, .44 American, .44 Russian, etcetera). The more potent .45 ACP is prone to overpenetrating, by modern standards, with nonexpanding ammo. The high velocity (at the time of it's introduction) 9mm Luger was again more then enough. Remember that at the time, the 9mm Kurz (.380) was quite popular.
Without expanding bullets, adding more powder behind the bullet would make sense to get a flatter trajectory and better range, but within the limits of handgun velocities, not much improved effect on target. However, with the switch to modern bullets, suddenly we require a lot of energy to just deform the bullet (you can get the idea of how much energy is expended doing this using a hammer), and then also push this much larger bullet to the necessary depth. So now you need much more kinetic energy to do the required work, hence +P offerings.
Saying the old 9mm did not work equals to saying that none of the old .36-38 calibers worked. This is obviously untrue, since these calibers were used for a century and something (both by civilians and militaries, and back then SMGs for close combat were a thing) before expanding bullets were even a thing, and .44-45 caliber offerings were "on the table" the whole time. However, a big factor in it's modern day popularity is, aside it's wide acceptance, the fact that the cartridge is energetic enough that it can spare the energy to expand and still penetrate sufficiently, especially if the pressure is jacked up a bit to +P levels. Lower power 9mm and .36-38 calibers do not have this spare power required to work well with expanding ammo and have generally fallen out of favour, with the exception of .38 Special which was considerably jacked up in it's +P specification.
Before the advent of expanding ammo, though, there was no real benefit to the 9mm Luger compared to most other calibers of the size, now it's the "minimum good caliber". Mind you, I've a soft spot for various .45s, but it has to be said that the 9mm sits in a "sweet spot" ballistically speaking. However that came to be only in relatively recent times, with the advances in ammo. There was nothing special about it - it was just another one of the .36-.38 family of cartridges - for a very long time.
