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The standard-issue, military .45 ACP cartridge contains a 230-grain bullet that travels at approximately {{Convert|830|ft/s|0|abbr=out}} when fired from the government-issue M1911A1 pistol, and approximately {{Convert|950|ft/s|0|abbr=out}} fired from the [[Thompson submachine gun|Thompson M1A1 submachine gun]]. The cartridge comes in various specialty rounds of varying weights and performance levels as well.<ref name="COTW14"/>
The cartridge operates at a relatively low maximum [[chamber pressure]] rating of {{Cvt|21000|psi|MPa|0}} (compared to {{Cvt|35000|psi|MPa|0|disp=sqbr}} for [[9×19mm Parabellum|9mm Parabellum]] and [[.40 S&W]], {{Cvt|37500|psi|MPa|0|disp=sqbr}} for [[10mm Auto]], {{Cvt|40000|psi|MPa|0|disp=sqbr}} for [[.357 SIG]]), which due to a low [[bolt thrust]] helps extend service life of weapons in which it is used. Some makers of pistols chambered in .45 ACP, do not certify them to use
In its non-expanding [[Full metal jacket (ammunition)|full metal jacket]] (FMJ) version, the .45 ACP cartridge has a reputation for effectiveness against human targets because of its heavy mass, having the capacity to penetrate tissue deeply, and damage the central nervous system. Its large 11.5 mm diameter creates a more substantial permanent wound channel versus smaller calibers, which can lower blood pressure rapidly if critical organs of the circulatory system are hit.
In its expanding [[jacketed hollow point|hollow point]] form, it is also particularly effective against human targets. In tests against ballistic gelatin, a 185-grain hollow point traveling at 1,050 feet per second and expanded to about .76 of an inch. This is a significantly large permanent wound cavity for a handgun projectile. For those who follow the energy dump and/or hydrostatic shock theories of wounding ballistics, this is ideal. While slightly decreasing penetration and likewise the chance of hitting a vital organ, a large diameter wound will cause more blood loss. There is also a reduced likelihood of overpenetration, meaning that it is more likely that the projectile will transfer all of its kinetic energy to the intended target, thus more reliably incapacitating them.
Drawbacks for military use include the cartridge's large size, weight, increased material costs in comparison to the smaller, flatter shooting NATO standard 9×19mm Parabellum cartridge, a cartridge which uses less powder, brass, and lead per round. Standard 9mm NATO ammunition has a more limited armor penetration capability—a deficiency shared with .45 ACP, whose large, slow bullet does not penetrate armor to any great extent. The low muzzle velocity also makes the bullet drop over long ranges, making hits more difficult; however, it is important to note that the vast majority of self-defense situations involving handguns typically occur at close ranges.
After two years of testing, one of the final FBI comments was that services that adopt (or stay with) .40 S&W or .45 ACP, did so at the risk of increased recoil and a possible reduction in accuracy as 9×19mm with premium quality ammunition had nearly exactly the same performance.<ref name="Grandview-FBI 9mm">{{cite web |title=Case Closed: FBI Says 9mm Is The Best Pistol Round |url=http://www.grandviewoutdoors.com/guns/case-closed-fbi-says-9mm-is-the-best-pistol-round/ |first=Christian |last=Lowe |date=September 26, 2014 |website=Grand View Outdoors |access-date=23 February 2017 |quote=There is little to no noticeable difference in the wound tracks between premium line law Auto enforcement projectiles from 9mm Luger through the .45 Auto. |archive-url=https://web.archive.org/web/20170215232656/http://www.grandviewoutdoors.com/guns/case-closed-fbi-says-9mm-is-the-best-pistol-round/ |archive-date=February 15, 2017 |url-status=live}}</ref> A factor rated by the recent FBI testing was accuracy and time to recover. The .45 ACP handguns ranked last, largely due to increased recoil.<ref name="Grandview-FBI 9mm"/>
===Use in suppressors===
As standard pressure .45 ACP rounds fired from handguns and submachine guns are inherently subsonic, it is one of the most powerful pistol calibers available for use in [[suppressor|suppressed weapons]] since subsonic rounds are quieter than supersonic rounds. The latter inevitably produce a highly compressed [[shock wave]], audible as a loud "crack", a small [[sonic boom]], while they travel through the air. Suppressors reduce the audible "report" by slowing and channeling the high speed gas generated by the burning/expanding gunpowder before it exits the muzzle resulting in a muffled "cough". Suppressors cannot act on a supersonic shock wave continuously generated by a bullet exceeding the {{cvt|1087|ft/s}} [[speed of sound]] at {{cvt|32|F}} ambient cold temperatures, as this shock wave is continuously produced throughout the entire flight path over which the bullet is supersonic, which extends long after it exits the barrel.
The downside to the use of .45 ACP in suppressed weapons is that increasing the diameter of the passage through a suppressor decreases the suppressor's efficiency; thus, while .45 ACP is among the most powerful suppressed pistol rounds, it is also one of the loudest. Most .45 ACP suppressors must be fired "wet" (with an [[Ablation|ablative]] medium, usually oil or water) to bring sound levels down to "hearing-safe" (under 140 [[Decibel|dB]], generally).<ref name="SSA">{{cite book |last=Truby |first=J. David |date=1987 |title=Silencers, Snipers, and Assassins...an Overview of Whispering Death |location=Boulder, Colorado |publisher=Paladin Press |page=216 |isbn=0-87364-012-8}}</ref>
==Magazine capacities==
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