In its traditional FMJ design at 115 to about 124 grains, there have been enough reports over the years to see that it can leave something to be desired in stopping determined adversaries. I'm aware of the reports saying that 9mm ball is practically equivalent to .45 ACP ball, but I cannot bring myself to accept that. While neither has proven to be particularly "good" on the animals I've shot, it's been my experience that .45 ACP 230-grain ball is a bit better than 9mm ball. That said, I've had Texas jackrabbits run after being hit midway in the torso with both. If required to use FMJ for "serious" purposes, I'd go with the larger caliber.
Today's 9mm shooter has a choice of expanding ammunition better than anything imagined decades ago. It actually works reliably in the real world. Left to Right: Federal std. pressure 115-gr. JHP, Corbon 115-gr. DPX +P, Hornady 124-gr. XTP, Winchester 127-gr. +P+, Remington 147-gr. GSHP and Speer 147-gr. GDHP.
The 9mm took its worst "hit" after the "Miami Fiasco" in which several FBI agents were killed after a felon armed with a .223 rifle continued to fight for several minutes after being shot with a 9mm Winchester 115-gr. Silvertip. The bullet penetrated an arm before entering the bad guy's side and stopped just short of hitting the heart. Despite the fact that this wound severed an artery and was later described as "not survivable," he fought on for several minutes. This incident brought on the search for more effective loads and resulted in at least two new handgun calibers. Combine the Miami failure with the past reports of 9mm "ineffectiveness" from the ball loads, and it's understandable why some would not regard the 9mm as a suitable defensive round.
Some things are overlooked in my opinion.
First, at the time, the call was for rapid expansion and concerns existed about over-penetration. The Winchester bullet acted as it was designed to; it expanded. The round usually penetrates about 13" in 10% ballistic gelatin, as does Federal 115-gr. JHP. Something not mentioned often is that many rounds were fired from the agents with very few hits. I am NOT being critical, but had these felons been hit perhaps better or with repeat shots, the agents might not have been killed. Unfortunately, the FBI agents took handguns to a rifle fight. A number of circumstances worked against them, but the fact remains that the 9mm bullet that did find its mark, failed. Some gun scribes have asked if it would've made any difference had the hit been with a larger caliber with some saying yes, while others say no. I don't know. I do know that the felons knew that either their capture or a fight was imminent for several minutes and suspect strongly that both had massive amounts of adrenaline flowing. I also believe that we expect an awful lot of any defensive handgun round when we count on an "instant stop." Hunters often see animals weighing less than a human being run after being solidly hit with a high-powered rifle round. While I'm not at all "happy" that the 9mm round failed in this example, there are examples of all caliber handguns failing to stop humans with good hits. Unfortunately, it just happens and will continue to do so. As Clint Smith of Thunder Ranch has said, "Some people just won't be impressed with your caliber."
Some believe that the "heavy bullet" approach is best with the 9mm and opt for a 147-gr JHP from the maker of their choice. Were I going this route, I'd probably go with either Winchester's law enforcement Ranger ammunition, Remington's 147-gr. Golden Saber or Speer's excellent Gold Dot Hollow Point. I believe that Hornady offers a 9mm in this weight with their XTP bullet as well.
Would the use of any of these rounds have made a difference in Miami? I don't know, but any of these would be more effective than ball and I believe that any are capable of delivering a telling blow with proper placement.
Corbon 125-gr. +P JHP has proven very accurate in several 9mm pistols I've tried it in. Though heavier than the same company's popular 115-gr. +P JHP, it uses a very aggressive expanding bullet made by Sierra. There are other 124 and 125-gr. JHP loads that will penetrate a bit more if this is your goal. I have no problem with the Corbon. Both it and the 115-gr. JHP penetrate approximately 10" of 10% ballistic gelatin. Winchester's 127-gr Ranger ammo penetrates approximately 15". Remington 147-gr Golden Saber averages about 16" or so. Speer Lawman 124-gr. Gold Dots average around 13" of penetration. Like Corbon's 115-gr. JHP +P, this is a maximum effort load.
I favor 9mm expanding ammunition that does about 10 to 12" of penetration, but am not upset with 12 to 14." Some opine that the bullets in the 10 to 12" range do the most damage while others have severe concerns of under-penetration should an intermediate object like an arm be stuck by the bullet on its way into the torso. It's my belief that in straight, head-on situations with no intermediate barriers, the rapid expanding JHP's getting about 10" penetration possibly do the most damage, but opt for just a tad more penetration capability in case I cannot get the head-on shot.
Frequently, people ask about super low-penetration rounds like the Glaser Safety Slug and Aguila IQ hollow points or Corbon's 90-gr. JHP +P. The later usually penetrates less than 6" before stopping and this is just a bit to shallow to my way of thinking. I don't recommend, suggest, or use these really lightweight-for-caliber bullets for serious purposes.
In a standard pressure 115-gr. load, I'd still go with Federal 115-gr. JHP. The round has an extremely feed reliable rounded ogive, is normally very accurate, and averages between 1140 to 1170 ft/sec depending upon pistol and ammunition lot. It penetrates about 13" of ballistic gelatin. The ballistically similar Winchester USA 115-gr. JHP averages around 14" penetration of ballistic gelatin. This bullet appears to be the Silvertip, but without the E-nickel finish. I cannot prove it, but I suspect this bullet's been "tweaked" for a tad more penetration. I seem to recall the Silvertip 115-gr. 9mm doing about 10" penetration in the past.
As stated above, I believe the 9mm to be quite ammo-dependent in terms of potential "effectiveness." I'll cast my lot with the warmer 124 - 127-gr. JHP's that have proven reliable and count on placement. The 9mm can be a capable defensive arm with "good" ammunition and the ability to get telling hits, perhaps repeated ones. In service size handguns, its relatively low felt-recoil aids in this capability.
Is the 9mm a good defensive round? Yes, I believe so in some loads.
Is it the best defensive handgun round? Probably not, but it might just be for some people as it has low recoil for the "power" delivered and most agree that this can contribute to accuracy. In my observation any of the commonly used defense calibers can fail and any of them can benefit from load choice. Certainly this includes 9mm but in my view, it includes the others, too.
If you do not trust 9mm and have a choice, go with something else. Confidence in one's equipment is important in my opinion.