In handgun circles, isn't that the most debated question? It's worse than Coke vs. Pepsi, Ford vs. Chevy, or UFC vs. Pride. What is more effective 9mm Parabellum, .45ACP, or .40S&W?
Punch in Penetration test 45 9mm 40 into Google and you get some 7,380,000 results. There is plenty of inaccurate information regarding ballistics/terminal performance disseminated on web forums, even those that are dedicated as LE only.
In looking at valid tests, a good place to get information from is the US government, long a source of heavy academic research into issues ranging from frog dimples to the number of craters on the moons of mars. The FBI's terminal-ballistic testing protocol evaluates a bullet's ability to pass through various intermediate barriers-from light clothing to automobile glass-and still expand and penetrate to a depth necessary to damage vital organs.
In 1989, they extensively tested more than 100 handgun loadings in multitudes of tests. These included 26 9mm rounds, 27 40S&W loadings, and 21 .45ACP selections.
Let us look at the results from penetration and expansion and see the rest of the story as Paul Harvey would say
According to the FBI's 1989 study into handgun effects, page 11 states that "It is essential to bear in mind that the single most critical factor [in handgun terminal ballistics] remains penetration. A handgun bullet MUST reliably penetrate 12-inches of soft body tissue as a minimum, regardless of whether it expands or not. If a bullet does not reliably penetrate to these depths, it is not an effective bullet for law enforcement use."
The above-mentioned FBI study quotes, the three hottest loadings in 9mm, 40S&W, and .45ACP all penetrated within 3-inches of each other.
In 9mm, the 115-grain CCI/Speer Gold Dot penetrated 22.6" when fired into clothed ballistic gelatin blocks. Only 4 of the 26 9mm loads tested penetrated less than 12-inches, all 115-grain low power loadings.
The Deepest penetrating 40-caliber S&W round was the Remington Golden Saber 180-grain, which penetrated 21.1". All 27 of the 40S&W rounds penetrated over 12-inches.
When the .45ACP is compared, Remington's 185-grain round penetrated 24.6" inches. As a revelation, two of the 21-45ACP rounds, both low-powered light loads, failed to penetrate more than 12-inches.
2009 USCG Study done at the Crane Weapons Center found that firing 40/9/45 caliber ammo from into Gelatin with 4 layers of clothing @ 10-feet brought the following, very similar results with standard issue ammunition available to Federal Law Enforcement agencies.
.40 Caliber Ammunition Penetrations in inches
9mm JHP - 115 grain 9.3"
9mm JHP - 147 grain 12.5"
40 Caliber JHP - 155 grain 10.3"
.45 ACP JHP - 230 grain 13.7"
Conclusion in the quest for a penetrator: It's a dead heat overall in penetration between the three rounds, with a slight nod going to the .45ACP and a word of warning about low powered, light rounds of any caliber.
Rapidly expanding hollow-pointed and ballistic tipped ammunition produces results, that gunfighter of the Wild West could only dream of. This rapid expansion leads to a larger wound cavity, which leads to the higher chances of a 'stop'. Let us compare the three argued about rounds as far as how wide they penetrate
The 9mm Gold Dot load mentioned above mushroomed to 0.69" (or 69-caliber if you will) in unclothed gel.
The biggest expanding 40S&W round in the FBI tests was the 165-grain Winchester Ranger PG, which went some 0.72" caliber in clothed gelatin. Three different 230-grain .45ACP loadings in the test expanded to 0.74", the maximum in the study.
When comparing 69 calibers to 74 caliber there is not a lot of room to side one way or the other. In the end, we are speaking of 5/100ths of an inch. Of course, those who have to have a winner would call the expansion category for the .45ACP by a nose.
Overall, the .45 ACP is marginally better expanding, as well as capable of slightly deeper penetration. However, when taken overall, the vaunted 40S&W and the humble and long-soldiering 9mm are neck and neck with the .45ACP.
Of course everyday cartridge manufacturers produce rounds that are hotter, expand further and penetrate deeper than last years, as is the nature of their ever-expanding industry. However, even when taking the dated 1989 study in mind, the idea that hot, quality rounds made by legitimate manufacturers for either 9mm, 40S&W, or .45ACP are very, very effective and produce a ballistically similar result.
It can be argued that 9mm is cheaper, and while for practice ammunition this is correct, however when good quality JHP ammunition is compared, almost any difference is relative.
The .45ACP and the 9mm have been around for more than 100-years and have proven themselves in dozens of armies and hundreds of law enforcement agencies around the world and throughout history. The 40S&W is a much newer round, often referred to as a blend between the two introduced in 1990. The 40 is by far one of the most trusted law enforcement rounds in the country and is used by hundreds of departments including most of the Federal LE agencies. All three calibers are established, effective, and dependable.
It should be remembered by all that determined individuals could sustain many gunshot wounds in areas that produce great pain and continue to fight a long time, even without the aid of drugs or alcohol.
Shot placement is everything in a gunfight and always the key to stopping a threat effectively, no matter the caliber.