Nomercy

Here are a few things I'd keep in mind when you're considering a self defense firearm, especially when compare guns based on capacity...

Military agencies, Law Enforcement agencies, and Civilians all have different rules of engagement and combat: LEO's will RARELY be demanded to draw their weapon, and even less often will they be required to fire it-they're required to fire when situation dictates, based on their safety or that of others...Military officers will fire nearly whenever they draw, and will expect to draw in ANY confrontation-they also may be required to initiate a hostile situation...Civilians will never expect to need to draw, most civilians never have to even if they carry, and even fewer ever are forced to fire if they're forced to draw-the reasons for a civilian to draw and shoot are the fewest of any of the three. Less than 10% of cases where a gun is drawn in self defense ends up with a shot fired, less than 2% of such cases require more than one shot-you aren't likely to need more than 1shot, let alone more than 6 (revolver) or 8(.45acp), likely if you need more than 6-8, you're either taking LONG shots at a running target, or you're in a stand off and you're probably going to need more than the extra 2rnds a 9mm gives you (either that or you're a TERRIBLE SHOT).

You've also got to remember that Military and LEO's are trained to shoot, most civilians aren't so lucky to be...although a .45acp is hard recoiling (for a pistol), the stopping power advantage dictates necessity for most agencies, so the "difficulties of shooting it" are overcome by regular practice, and lots of it. (buying a .45acp because of it's stopping power is useless if you can't shoot it accurately, Grits Grisham once coined, "a .22lr in the eye is more effective than a .45acp in the knee," if you can't control the gun, it's not doing you any good, you can take the time to LEARN to control it, but you've got to do it.)

Military/LEO's normally have armed back-up or other soldiers present, you won't. If you for some reason should run dry, no one will cover you when you reload (Like I said, you'll never need that many shots, but if you'd ever need to reload, repacking a single action revolver is harder than a auto, and you'd get 20rnds for your time with a 9mm instead of 16rnds with a .45acp)

Military and some LEO's should expect to face multiple armed and hostile assailants in any given scenario, you will likely be one on one and won't likely be met with withstanding returned fire. (a LEO or Military officer needs a lot of stopping power on each shot, they need to alleviate each threat quickly and move on to the next, they can't afford to empty an entire mag into one assailant just to stop them before reloading and moving on to the second of 6 assailants...they usually pick a .45acp because it's known for stopping power, one or two shots and the recipient is no longer a threat, a 9mm is more likely to require more shots to stop a threat, so even though they get 2more rounds with it, they'll be more likely to have to reload under fire, which is never handy. Once you fire one shot, you're not likely to get more than one or two back at you before your assailant high tails it out of there, you're not going to get prolonged return fire, so stopping the threat immediately in one shot isn't necessarily as important-and since you're likely to only face one opponent, you don't have to conserve ammo, put 8+rnds of even 25acp Center Of Mass on an assailant and they're going down, you don't necessarily need a powerful .45acp.)

Military/LEO's will be in drastically different condition than civilians during a "gun fight", they've got to be prepared (especially military) to make shots from point blank to 50yrds or so. You're not going to be taking long range shots at anyone, if they're that far off, they're running away, and you'll be sued for continuing fire, you don't need to consider the extra down range energy of the .45acp because you're not going to be shooting down range-your actoin will be up close and personal. They're also trained to react if surprised, and they'll know to be on edge and have their weapon drawn and ready when going into a building after hostiles, while waiting out a gunman in a store or waiting in a bunker on an ambush, etc, they are trained to move using cover, they're likely to be wearing some sort of body armor, and if they're waiting anywhere, they're barricaded using effective cover-you're likely to be surprised and scared, likely to be in bed asleep-groggy and disoriented, in the dark, your gun will not be in your hand, the safety won't be off, it might not be loaded, you're not trained to be "intimate" with it, and you'll have to react faster than the trained personnel-find a gun that's easy to use, a double action revolver is great for ease of use, but you have to keep it loaded all the time, not safe if you have kids, an auto can be loaded faster, but is a bit more complex to use, and there are varying degrees of difficulty within different models.

Military personnel aren't likely to get sued for colateral casualties, LEO's are less vulnerable than civilians, but still must consider it. (you shoot through a wall and kill your neighbor, you're going to jail, accident or not).

(all that said, only the Air force continues to regularly issue 9mm's to officers, this doesn't include special ops or irregular issues, but on the whole, the rest of the Corps have returned to the .45--most LE agencies prefer the .45, but are quickly turning towards the .40S&W for it's ease of shooting vs. the .45acp and increased stopping power vs. the 9mm, it's kind of like the 16ga-all the power of the 12ga with the kick of the 20ga, it's ALMOST the power of the 45 but with the kick of the 9mm.)

Long story short, get what fits your hand the best, what you can use the easiest, and the most powerful round you can effectively control. It's sometimes good to base your decisions off what Military and LE agencies use, but you've got to remember they're playing in a different league, you're in a whole different rule set than they are, in some ways it's easier, it others, it's a lot worse for civilians.