When it comes to 10mm vs 9mm for self-defense, 9mm pretty much wins.
That is, against humans.
Prior to the 1990s, handgun ammunition just wasn’t what it was today. Many police departments, federal agencies, and armed civilians found that 9mm ammunition just didn’t do what they needed it to do when it needed to do it, for the most part. If you got your hands on some Corbon DPX or SuperVel JHP, that was a different story, but hardly anyone could get it.
Back in those days, spanking a bad person with a bigger bullet was the preferred medicine when one relied on a semi-auto for their personal protection. .45 ACP ruled the roost, and 10mm and later .40 S&W were cooked up as compromises between 9mm and the larger rounds. In that era, larger-caliber bullets tended to perform better, especially JHP rounds.
Handgun ammunition improved dramatically in the 1990s. When Federal HST, Speer Gold Dot, Winchester Black Talon and other rounds hit the market, 9mm terminal performance improved DRAMATICALLY. Since then, the gap has closed completely; today’s 9mm JHP performs as well in the real world as JHP rounds of larger calibers when – and this is the key – placed accurately.
Granted, .45 ACP and .40 S&W and 10mm are just as ineffective when you don’t hit vital areas.
As a result, real-world studies have found stoppage rates are pretty much the same across all handgun rounds from 9mm to .44 Magnum. It all depends on where you put the bullet, and whom you put it into as psychological shock, more often than not, is what stops most humans in a gunfight. When it isn’t, caliber barely matters; any round 9mm or larger does the trick, again, when placed accurately.
So, for self-defense against two-legged threats, there is no advantage to shooting 10mm in terms of terminal performance. There is some evidence that shootings in low-light conditions stop more quickly due to psychological shock caused by greater muzzle flash, which would favor 10mm (bigger bullet, bigger boom, bigger flame) but that’s hardly a good reason to carry it.
As a personal protection round, 9mm is just as effective in the real world, cheaper to shoot ($10 a box vs $20+ a box) and easier on the shooter. Again, against humans.
But what about off the beaten path?
As a woods round, 9mm stinks. It’s barely effective on deer, it’s too much for small game (a rabbit or grouse will just explode and that’s disgusting) and while it has been used to deal with bears including grizzlies…you wouldn’t want to bet the house on it. 10mm is a proven handgun hunting cartridge, and is right popular in Alaska, where a lot of people carry it in bear country and has been proven in that role as well provided good ammunition selection and careful placement.
As mentioned above, 10mm has less drop at distance, and can be loaded a whole heck of a lot hotter. In any application where those things matter, meaning outdoor applications, 10mm vs 9mm is decided wholly in favor of the bigger bullet.
Source: Alien Gear Holsters