View source for .45 ACP

{{short description|Pistol cartridge designed by John Moses Browning}}
{{Distinguish|.45 Colt}}
{{Use mdy dates|date=July 2014}}
{{Infobox firearm cartridge
|name= .45 ACP
|image= File:Cartridge .45 ACP CC BY-SA 4.0 by Grasyl.jpg
|image size = 220px
|caption= .45 ACP cartridge [[full metal jacket (ammunition)|full metal jacket]]
|origin=[[United States]]
|type= [[Pistol]]
<!-- Production info -->
|designer= [[John Browning]]
|design_date= 1904
|production_date = 1905–present
|manufacturer=
|parent=
|variants= [[Overpressure ammunition#Commercially available .2BP cartridges|.45 ACP +P]], [[.45 Auto Rim]], [[.45 Super]], [[.460 Rowland]]
|wars= [[World War I]] – present
|case_type= Rimless, straight
|bullet= .452
|land= .442
|neck= .473
|shoulder=
|base= .476
|rim_dia= .480
|rim_thick= .049
|case_length= .898
|length= 1.275 
|case_capacity= 25 - 27.4
|rifling= 1 in {{cvt|16|in|0}}
|primer= Large pistol LP (some makers are now using small pistol SP)
|max_pressure=19000
|pressure_method=CIP
|max_pressure2=21000
|pressure_method2=SAAMI
<!-- Ballistic performance -->
|is_SI_units=
|bw1=230
|btype1=FMJ, Winchester
|vel1=835
|en1=356
|bw2=165
|btype2=Hydra-shok, Federal
|vel2=1060
|en2=412
|bw3=230
|btype3=FMJ, Double Tap
|vel3=960
|en3=471
|bw4=185
|btype4=JHP +P, Underwood
|vel4=1200
|en4=592
|bw5=90
|btype5=TFSP, RBCD
|vel5=2036
|en5=829
}}

The '''.45 ACP''' ([[Automatic Colt Pistol]]), also known as '''.45 Auto''', '''.45 Automatic''', or '''11.43×23mm'''<ref>{{Cite book |title=Handbook of Handguns |last=Strickland |first=Jeffrey |page=151 |date=2014 |publisher=LULU.COM |isbn=978-1-300973294 |location=[S.l.]|oclc=1020871429}}</ref> is a [[Rim (firearms)#Rimless|rimless]] straight-walled handgun [[Cartridge (firearms)|cartridge]] designed by [[John Moses Browning]] in 1904, for use in his prototype [[Colt's Manufacturing Company|Colt]] [[semi-automatic pistol]]. After successful military trials, it was adopted as the standard chambering for Colt's [[M1911 pistol]].<ref name="COTW14">{{cite book |last1=Barnes |first1=Fred C. |title=Cartridges of the World |date=2014 |publisher=[[Krause Publications]] |location=Iola, WI |isbn=978-1-4402-4265-6}}</ref> The round was developed due to a lack of [[stopping power]] experienced<ref>{{Cite web |last=Tong |first=David |date=2020-11-07 |title=History of the .45 ACP Cartridge |url=https://www.ammoland.com/2020/11/history-45-acp-cartridge/ |access-date=2021-06-17 |website=AmmoLand.com |language=en-US |archive-date=January 28, 2021 |archive-url=https://web.archive.org/web/20210128053727/https://www.ammoland.com/2020/11/history-45-acp-cartridge/ |url-status=live }}</ref> in the [[Moro Rebellion]] in places like [[Sulu]]. The issued ammunition, [[.38 Long Colt]], had proved inadequate, motivating the search for a better cartridge. This experience and the [[Thompson–LaGarde Tests]] of 1904 led the Army and the Cavalry to decide that a minimum of .45 caliber was required in a new handgun cartridge.

The standard-issue military .45 ACP cartridge uses a {{convert|230|gr|g oz|abbr=on|lk=on}} round-nose bullet at approximately {{convert|830|ft/s|m/s|abbr=on}} fired from a government-issue M1911A1 pistol. It operates at a relatively low maximum [[chamber pressure]] rating of {{Cvt|21000|psi|MPa|lk=on}}, compared to {{Cvt|35000|psi|MPa|lk=on}} for both [[9×19mm Parabellum|9mm Parabellum]] and [[.40 S&W]], which due to a low [[bolt thrust]] helps extend the service lives of weapons. Since standard-pressure .45 ACP rounds are subsonic when fired from [[handgun]]s and [[submachine gun]]s, it is a useful caliber for [[silencer (firearms)|suppressed]] weapons as it lacks the [[sonic boom]] inherent to supersonic rounds.

==Design and history==
[[File:.45 ACP U.S. Army ball cartridge diagram.jpg|thumb|left|Cross-sectional diagram of U.S. Army .45 ACP  ball cartridge for the Model 1911 pistol, with dimensions in inches]]
During the late 19th century and early 20th centuries, the [[United States Cavalry]] began trials to replace their sidearm arsenal of issued [[Colt Single Action Army|Single Action Army]] (SAA) in favor of the more modern and versatile [[Revolver#Double-action|double-action revolver]] in [[.45 Colt]].

After the example of the Cavalry, the Army in turn had fielded versions of double-action revolvers in [[.38 Long Colt]]. It was eventually decided that the .38-caliber round was significantly less effective in overall "stopping power" than the .45 Automatic against determined opponents, such as the Tausug [[Moro people|Moro]] [[juramentado]] warriors, who were encountered in the [[Moro Rebellion]].<ref name="DK2006">{{cite book |author=DK |title=Weapon: A Visual History of Arms and Armor |url=https://books.google.com/books?id=Px5E3EIF5jQC&pg=PA290 |date=2 October 2006 |publisher=[[DK (publisher)|DK Publishing]] |isbn=978-0-7566-4219-8 |page=290 |access-date=August 26, 2016 |archive-url=https://web.archive.org/web/20170322080306/https://books.google.com/books?id=Px5E3EIF5jQC&pg=PA290 |archive-date=March 22, 2017 |url-status=live}}</ref><ref name="The2008">{{cite book |author=The Green Muse Writers Collective |title=Keep Calm Carry on: A Survival Guide |url=https://books.google.com/books?id=auxpWQox1j8C&pg=PA138 |date=December 2008 |publisher=iUniverse |isbn=978-1-4401-0249-3|page=138}}</ref><ref>{{cite web |url=http://www.manilatimes.net/juramentados-and-the-development-of-the-colt-45-caliber-model-1911/107609/ |title=Juramentados and the development of the Colt .45 caliber Model 1911 |website=[[The Manila Times]] Online |date=2014-06-29 |access-date=August 26, 2016 |archive-url=https://web.archive.org/web/20160915083326/http://www.manilatimes.net/juramentados-and-the-development-of-the-colt-45-caliber-model-1911/107609/ |archive-date=September 15, 2016 |url-status=live}}</ref><ref>{{Cite journal |url=http://www.bagongkasaysayan.org/saliksik/wp-content/uploads/2014/11/13-Artikulo-Lasco.pdf |title=Ang "Kalibre 45" At Ang Pakikibaka Ng Mga Mandirigmang Pilipino |trans-title=The "Kaliber 45" and The Struggle of the Filipino Warriors |language=fil |first=Lorenz |last=Lasco |date=November 2014 |journal=Saliksik |volume=3 |number=2 |pages=275–306 |access-date=January 8, 2018 |archive-url=https://web.archive.org/web/20161009151138/http://www.bagongkasaysayan.org/saliksik/wp-content/uploads/2014/11/13-Artikulo-Lasco.pdf |archive-date=October 9, 2016 |url-status=dead}}</ref> The standard-issue rifle, the [[.30-40 Krag]], had also failed to stop Moro warriors effectively;<ref>{{cite web |url=http://www.sightm1911.com/1911%20History.htm |title=History of the M1911 Pistol |website=Sight M1911 |url-status=dead |archive-url=https://web.archive.org/web/20060716083501/http://www.sightm1911.com/1911%20History.htm |archive-date=July 16, 2006}}</ref> the British had similar lack-of-stopping-power issues switching to the [[.303 British]], which resulted in the development of the ''[[Expanding bullet|dum-dum]]'' bullet, in an attempt to compensate for the round's deficiencies. This experience, and the [[Thompson–LaGarde Tests]] of 1904, led the Army and the Cavalry to decide a minimum of .45-caliber was required in a new handgun. Thompson and Major [[Louis La Garde]] of the medical corps arranged tests on cadavers and animals in the Chicago stockyards, resulting in their declaring that the .45 was the most effective pistol cartridge. They noted, however, training was critical to make sure a soldier could score a hit in a vulnerable part of the body.

Colt had been working with Browning on a [[10 mm caliber|.41 caliber]] cartridge in 1904, and in 1905, when the Cavalry asked for a .45-caliber equivalent, Colt modified the pistol design to fire an enlarged version of the prototype .41 round. The result from Colt was the Model 1905 and the new .45 ACP cartridge. The original round that passed the testing fired a {{Convert|200|gr|0|adj=on|lk=out}} bullet at {{Cvt|900|ft/s|0}}, but after a number of rounds of revisions between [[Winchester Repeating Arms Company|Winchester Repeating Arms]], [[Frankford Arsenal]], and [[Remington Arms|Union Metallic Cartridge]], it ended up using a {{Convert|230|gr|0|adj=on}} bullet fired at a nominal velocity of {{Cvt|850|ft/s|0}}. The resulting .45 caliber cartridge, named the ".45 ACP", was similar in performance to the [[.45 Schofield]] cartridge and only slightly less powerful while significantly shorter than the .45 Colt cartridge that the United States Cavalry was using at the time.

By 1906, bids from six makers were submitted, among them, Browning's design, submitted by Colt. Only [[Deutsche Waffen und Munitionsfabriken|DWM]], [[Savage Arms|Savage]], and Colt made the first cut. DWM, which submitted two [[Luger pistol]]s chambered in .45 ACP, withdrew from testing after the first round of tests, for unspecified reasons.<ref name="back">{{cite web |url=http://www.sightm1911.com/lib/history/background.htm |title=Background Information on the M1911 .45 Caliber Pistol |first=David L. |last=Velleux |website=Sight M1911 |access-date=May 16, 2007 |archive-url=https://web.archive.org/web/20070514053639/http://www.sightm1911.com/lib/history/background.htm |archive-date=May 14, 2007 |url-status=live}}</ref>

During the second round of evaluations in 1910, the Colt design passed extensive testing with no failures, while the Savage design suffered 37 stoppages or parts failures.<ref name="back"/> The Colt pistol was adopted as the [[M1911 pistol|Model 1911]].

The cartridge-pistol combination was quite successful but not satisfactory for U.S. military purposes. Over time, a series of improved designs were offered, culminating in the adoption in 1911 of the "Cal. 45 Automatic Pistol Ball Cartridge, Model of 1911", a {{convert|1.273|in|mm|0|adj=mid|-long}} round with a bullet weight of {{convert|230|gr|0}}. The first production, at [[Frankford Arsenal]], was marked "F A 8 11", for the August 1911 date.

The cartridge was designed by John Browning for Colt, but the most influential person in selecting the cartridge was Army ordnance member General [[John T. Thompson]]. After the poor performance of the Army's .38 Long Colt pistols evidenced during the [[Philippine–American War]] (1899–1902), Thompson insisted on a more capable pistol cartridge.<ref>{{Cite book |title=Handbook of Handguns |last=Strickland |first=Jeffrey |page=153 |date=2014 |publisher=LULU.COM |isbn=978-1-300973294 |location=[S.l.] |oclc=1020871429}}</ref>

===Military cartridges===
====U.S. military====
[[File:Caliber .45 Ball M1911.jpg|thumb|11.43x23 mm Automatic Colt Pistol Mod. 1911 (Peters Cartridge Co, USA)]]
The "T" (trials) designation was used for the experimental version of a cartridge and "M" (model) is used for the accepted and standardized version.
It came in either 24-round revolver ammo cartons, containing eight 3-round "half-moon" clips (1917-1945), pre-war 20-round cartons (1911-1942), or wartime 50-round cartons (1942–present). The M12 and M15 shotshell rounds were packed in 20-round cartons sealed in heat-sealed foil-lined Kraft paper.     
:''Caliber .45 ball M1911'' was the standard full-metal jacketed lead-core bullet.     
:''Caliber .45 dummy M1921'' has a hole drilled through the case and does not have a primer.  
:''Caliber .45 blank M9'' has a tapered case and does not have a bullet.
:''Caliber .45 shot M12(T23)'' (1943-1944 ) was a survival round with a round-nosed red [[wax paper]] projectile containing 118 pieces of No. 7 {{frac|1|2}} birdshot. It was issued in USAAF survival kits<ref group="note">The ammunition was packed in USAAF B-2 and B-4 emergency kits and C-1 survival vests.</ref> to allow pilots and aircrew armed with the Colt M1911A1 to use it for hunting small game.<ref group="note">The trials cartons originally had the instructions "Use only for hunting game. Do not use against enemy troops" in both English and either German or Japanese on the front. This was later changed to "For use in hunting small game, effective range {{convert|25|ft|m|disp=sqbr}}" and the foreign language text was dropped.</ref> The shotshell was a little longer than a standard round, so the operator had to load it in the action individually.<ref group="note">Text on the instructions slip packed with the ammunition carton (the last sentence is from the reverse side of the slip): "Instructions: This cartridge is intended for killing small game. Because of {{as written|i|t's [sic]}} length it will not feed in magazines, and each round must be loaded by hand. To load in the automatic pistol, draw slide back and lock in rearward position. Insert cartridge in chamber. [Depress slide stop, allowing slide to move forward.]"</ref> It was extracted after firing by removing the magazine, pulling back the slide, and pushing down on the case until it fell down the magazine well.<ref group="note">Text on the reverse of the instructions slip packed with the ammunition carton: "Instructions [...] If it be necessary, to remove an unfired cartridge from pistol, remove magazine, draw slide back and push downward on cartridge, allowing it to fall out through magazine slot."</ref> Reports showed that the paper projectile was affected by humidity and would swell or break apart. It was made limited standard until replaced by the .45 M15 shot cartridge.   
:''Caliber .45 shot M15'' was an improved survival round loaded with 108 pieces of No. 7{{frac|1|2}} birdshot, with wadding and a [[vermilion]] cardboard disc sealing the casemouth. It was loaded and extracted exactly like the M12 shot cartridge. 
:''Caliber .45 tracer M26 (T30)'' has a red tip. The round was designed as a short-ranged red flare for use in emergency signalling.

====Commonwealth military====
"S.A." stands for small arms. The "z" in the designation stands for cartridges loaded with [[nitrocellulose]] rather than [[cordite]].
:''Cartridge, S.A., pistol, .45-inch Colt Automatic, ball'' (1917) was the British designation used for American-manufactured ammunition. The Royal Navy had purchased a shipment of M1911 pistols in 1917 along with enough ammunition for evaluation, training and service purposes. It was never standardized by the Lists of Changes, but was mentioned in the Vocabulary of Priced Stores. It came in seven-round packets and was manufactured by Winchester. 
:''Cartridge, S.A., .45-inch, ball Mk Iz'' (1940–1945) was the designation used for American-manufactured ammunition and proposed British manufacture of .45 M1911 ball. Lend-lease ammunition came in commercial 42-round yellow Winchester or 50-round white Western Cartridge Company cartons. U.S. military-issue ammunition came in 20-round cartons, shifting to larger 50-round cartons in early 1942. It was never manufactured in Britain because it was readily available from American forces.
:''Cartridge, S.A., .45-inch, ball Mk IIz'' (1943) was a variant proposed for the Royal Navy, but never put into production. 
:''Cartridge, S.A., .45-inch A. C., ball'' (1942–1946) was the Canadian designation for their domestically manufactured ammunition for use in the European theater. It came in a plain 42-round carton that mimicked the capacity and dimensions of the yellow commercial Winchester ammunition cartons sold to Britain through Lend-lease.
:''Cartridge, S.A., .450-inch, ball Mk IIz'' (1943–1956) was the Australian designation used for their domestically-manufactured ammunition for use in the Pacific theater. It came in 24-round cartons.

====French Union military====
:''Cartouche de 11,43 mm, Pour Pistolets'' ('11.43 mm cartridge for pistols'): ''Balle ordinaire'' ('ordinary ball') pistol ammunition. Post-war production for use in the pistols and submachine guns given out by the US as military aid. It came in 25-round cartons.

==Cartridge dimensions==
The .45 ACP has {{convert|25|–|27.4|gr|g|lk=in}} of {{H2O-nl}} cartridge case capacity, depending on manufacturer and production lot.
[[File:.45 ACP cross section (3D model).png|thumb|.45 ACP cross section]]
[[File:.45 ACP dimensions.svg|500x500px|.45 ACP cartridge dimensions]]

45 Auto maximum CIP cartridge dimensions.<ref name="C.I.P. TDCC">{{cite web |url=http://www.cip-bobp.org/homologation/uploads/tdcc/tab-iv/tabivcal-en-page76.pdf |title=C.I.P. TDCC sheet .45 Auto |website=[[C.I.P.]] |access-date=November 13, 2016 |archive-url=https://web.archive.org/web/20160804075652/http://www.cip-bobp.org/homologation/uploads/tdcc/tab-iv/tabivcal-en-page76.pdf |archive-date=August 4, 2016 |url-status=dead}}</ref> All sizes are in millimeters (mm).

[[File:45acp SAAMI.jpg|500px|SAAMI specifications for .45 ACP. All dimensions are in inches (millimeters):]]

SAAMI specifications for 45 Automatic.<ref>{{cite web |url=https://saami.org/wp-content/uploads/2019/02/ANSI-SAAMI-Z299.3-CFP-and-R-Approved-2015-12-14-Posting-Copy.pdf |url-status=dead |title=Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Pistol and Revolver Ammunition for the Use of Commercial Manufacturers |website=[[SAAMI]] |access-date=October 1, 2019 |archive-date=October 2, 2019 |archive-url=https://web.archive.org/web/20191002031427/https://saami.org/wp-content/uploads/2019/02/ANSI-SAAMI-Z299.3-CFP-and-R-Approved-2015-12-14-Posting-Copy.pdf }}</ref> All dimensions are in inches (millimeters)

The common [[rifling]] [[twist rate]] for this cartridge is 1 in {{Cvt|16|in|0}}, 6 grooves, Ø lands = .442 in (11.23&nbsp;mm), Ø grooves = 45 in (11.43&nbsp;mm), land width = .147 in (3.73&nbsp;mm) and the [[Primer (firearm)|primer type]] is large pistol.
The cartridge [[Headspace (firearms)|headspaces]] on the mouth of the case at the L3 [[datum reference]].<ref name="wilson">{{cite book |last=Wilson |first=R.K. |date=1990 |title=Textbook of Automatic Pistols |location=Plantersville, South Carolina |publisher=Small Arms Technical Publishing Company |page=229 |isbn=0-935632-89-1}}</ref>

According to [[Commission internationale permanente pour l'épreuve des armes à feu portatives]] (CIP) rulings, the .45 ACP cartridge case can handle up to {{cvt|131|MPa|psi|lk=on}} P<sub>max</sub> piezo pressure. In CIP-regulated countries every pistol cartridge combination has to be [[Proof test|proofed]] at 130% of this maximum CIP pressure to certify for sale to consumers. This means that .45 ACP chambered arms in CIP-regulated countries are currently (2016) proof-tested at {{cvt|170|MPa|psi}} PE piezo pressure.<ref name="C.I.P. TDCC"/>

The [[SAAMI]] pressure limit for the .45 ACP is set at {{cvt|21000|psi|MPa|2}} piezo pressure,<ref>{{cite web |url=http://www.leverguns.com/articles/saami_pressures.htm |title=SAAMI Pressures |website=Leverguns.com |access-date=November 29, 2007 |archive-url=https://web.archive.org/web/20071014041459/http://leverguns.com/articles/saami_pressures.htm |archive-date=October 14, 2007<!--Added by DASHBot-->}}</ref> while the SAAMI pressure limit for the [[Overpressure ammunition#Commercially available .2BP cartridges|.45 ACP +P]] is set at {{cvt|23000|psi|MPa|2}}, piezo pressure.

==Performance==
The .45 ACP is an effective combat pistol cartridge. It combines accuracy as well as stopping power for use against human targets, has relatively low muzzle blast and flash, and it produces moderate [[recoil]] in handguns (made worse in compact models or with hot loads).
The .45 ACP is generally considered to have greater stopping power than the 9mm.{{citation needed|date=July 2023}} Due to its larger size and slower velocity it creates a larger wound channel and transfers more energy to the target.

The standard-issue, military .45 ACP cartridge contains a {{convert|230|gr|g|adj=on}} 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 +P ammunition.

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&nbsp;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 {{convert|185|gr|g|adj=on}} hollow point traveling at {{convert|1,050|ft/s|m/s}} expanded to about {{convert|.76|in|mm}}. 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, and 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 more 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&nbsp;[[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==
Magazine capacity varies depending on the type of firearm. Standard (not extended) single-stack magazines for pistols based on the 1911 design commonly, hold eight rounds or fewer in .45 ACP. Many modern pistols, such as the [[Glock#.45_ACP|Glock 21]], have adapted the cartridge into double-stacked magazine designs to increase ammo capacity, though this increases the pistol grip's girth. [[Drum magazine]]s used mostly for submachine guns have a capacity of 50 or 100 rounds.

==Adoption==
[[File:45 ACP - FMJ - SB - 1.jpg|thumb|.45 ACP pistol cartridge, FMJ bullet]]
Several US tactical police units still use the .45 pistol round.<ref name="SPTF">{{cite book |title=Special Police Task Forces |last=Diez |first=Octavio |year=2000 |page=40 |publisher=Lima Publications |isbn=978-84-95323-43-9}}</ref><ref name="janes">{{cite book |title=Jane's Gun Recognition Guide |edition=2nd |editor-last=Hogg |editor-first=Ian |page=113 |date=2000 |publisher=Harper Collins Publishers}}</ref><ref name="AmeHand">{{Cite magazine |url=http://www.findarticles.com/p/articles/mi_m0BTT/is_144_24/ai_57886947 |title=Most Wanted |last=Hopkins |first=Cameron |date=January 2000 |magazine=[[American Handgunner]] |access-date=February 21, 2007 |archive-url=https://web.archive.org/web/20041209014701/http://www.findarticles.com/p/articles/mi_m0BTT/is_144_24/ai_57886947 |archive-date=December 9, 2004 |url-status=dead}}</ref> While high capacity firearms are available in .45 ACP, the greater length and diameter of the .45 ACP means that the grip of the pistol must be longer and wider than the grip of a comparable pistol of a smaller caliber, such as 9×19mm Parabellum; this increase in grip size can make the pistol difficult to use for shooters with smaller hands.

Today, most NATO militaries use sidearms chambered for the [[9×19mm Parabellum]] cartridge, but the effectiveness of the .45 ACP cartridge has ensured its continued popularity with large-caliber sport shooters, especially in the [[United States]].<ref name="COTW">{{cite book |last1=Barnes |first1=Frank C. |last2=Skinner |first2=Stan |title=Cartridges of the World |edition=10th Revised & Expanded |publisher=Krause Publications |year=2003 |page=528 |isbn=978-0-87349-605-6}}</ref> In addition, select military and police units around the world still use firearms firing the .45 ACP.<ref name="COTW"/> In 1985, the .45 ACP M1911A1 pistol was replaced by the [[Beretta M9]] 9mm pistol as the main sidearm of the U.S. military, although select Special Operations units continue to use the [[M1911 pistol|M1911A1]] or other .45 ACP pistols.

==Load variants==
Rounds are available from {{convert|68|to|300|gr|g|adj=on}} with a common load being the standard military loading of a {{convert|230|gr||adj=on}} FMJ bullet (for comparison, the most common [[9×19mm Parabellum|9mm]] load is {{convert|115|gr|}}, half the weight). Specialty rounds are available in weights under {{convert|100|gr|}} and over {{convert|260|gr|}}; popular rounds among reloaders and target shooters include {{convert|185|to|230|gr|g|adj=on}} bullets.<ref>{{Cite web |url=http://www.bullseyepistol.com/reloads.htm |title=Reloading Data for Pistol Competition |first=John |last=Dreyer |website=Encyclopedia of Bullseye Pistol |access-date=2022-12-19 |archive-date=March 29, 2023 |archive-url=https://web.archive.org/web/20230329142547/http://bullseyepistol.com/reloads.htm |url-status=live }}</ref><ref>{{Cite web |url=https://stevespages.com/451p_1.html |title=451p_1 |website=Stevespages.com |access-date=2022-12-19 |url-access=subscription}}</ref> Target shooters competing in Bullseye Pistol (aka [[NRA Precision Pistol|Precision Pistol]]) find that .45 ACP ammunition using light bullets (12 to 13 g) and low velocities paradoxically generates less recoil than 9mm ammunition of equivalent accuracy, despite its larger caliber, and allows better scores in sustained fire.  Hollow-point rounds intended for maximum effectiveness against live targets are designed to expand upon impact with soft tissue, increasing the size of the permanent cavity left by the bullet as it passes through the target.

[[Tracer ammunition]] for the .45 ACP was manufactured by [[Frankford Arsenal]] and by [[Remington Arms]]. This ammunition was available to the [[United States Border Patrol]] as early as 1940 and was used through [[World War II]] for emergency signalling by downed [[United States Navy]] and [[United States Marine Corps|Marine Corps]] air crew. Tracer ammunition was identified by painting the bullet tip red.<ref name="nra">{{cite magazine |title=45 ACP Tracers |first=Dave |last=Andrews |date=February 2002 |magazine=[[American Rifleman]] |volume=150 |number=2 |page=20}}</ref>

=== Plus P ===
Most ammunition manufacturers also market what are termed "+P" (pronounced "plus P", designating [[overpressure ammunition]]) loadings in pistol ammunition, including the .45 ACP. This means the cartridge is loaded to a higher maximum pressure level than the original [[SAAMI]] cartridge standard, generating higher velocity and more muzzle energy. In the case of the .45 ACP, the new standard cartridge pressure is {{cvt|21000|psi|MPa|0}} and the SAAMI .45 ACP +P standard is {{cvt|23000|psi|MPa|0}}. This is a common practice for updating older cartridges to match the better quality of materials and workmanship in modern firearms.<ref name="COTW"/>

The terminology is generally given as "45 ACP +P" and sometimes, but not always, appears on the [[headstamp]]. These cartridges have the same external dimensions as the standard-pressure cartridges and will chamber and fire in all firearms designed for the standard-pressure loadings. The inner dimensions of the +P cartridge are different from the standard-pressure cartridge dimensions and thus allows for higher pressures to be safely achieved in the +P cartridge. If +P loadings are used in firearms not specifically designed for them, they may cause damage to the weapon and injuries to the operator.

===Others===
Popular derivative versions of the .45 ACP are [[.45 Super]] and [[.460 Rowland]].<ref name="COTW"/> The Super is dimensionally identical to the .45 ACP; however, the cartridge carries a developer established pressure of {{cvt|28500|psi|MPa|0}} and requires minor modification of firearms for use. The Rowland operates at a developer established {{cvt|40000|psi|MPa|0}} [[SAAMI]] and may only be used within a select group of firearms significantly modified for this purpose; the Rowland case is {{convert|0.057|in|0}} longer specifically to prevent it from being chambered in standard .45 ACP firearms. Brass cases for each of these cartridges carry the applicable name within the headstamp. The Super provides approximately 20% greater velocity than the .45 ACP +P; the Rowland approximately 40% greater velocity than the .45 ACP +P.<ref name="COTW"/>

==Synonyms==
{{div col}}
*45 (colloquial in English, Spanish, and Tagalog)
*.45 ACP (Automatic Colt Pistol)
*.45 Rimless Smokeless
*.45 Auto
*45 Auto. Colt / 45 AC (Winchester Repeating Arms Company)
*11.43×23&nbsp;mm (Metric)
*11.43 (Mexico, [[Obregón pistol]])
*11.25&nbsp;mm (Norway and<ref>[[:File:Kongsberg Colt.jpg|Kongsberg Colt - Norwegian M1914]]</ref> Argentina<ref>[[:File:Marcajes ea.jpg|Español: Evolucion de los marcajes de las pistolas sistema Colt del ejercito Argentino]]</ref>)
*11&nbsp;mm 43 (France)
*11&nbsp;mm (Southeast Asia)<ref>{{cite news |url=https://www.bangkokpost.com/news/crime/1446430/man-shot-injured-by-fugitive-gunman |title=Fugitive gunman shoots drug-taking relative |work=[[Bangkok Post]] |archive-url=https://archive.today/20221123154733/https://www.bangkokpost.com/thailand/general/1446430/man-shot-injured-by-fugitive-gunman |archive-date=23 November 2022 |date=15 April 2018 |last=Rakrun |first=Nujaree}}</ref><ref>{{cite news |url=https://www.bangkokpost.com/thailand/general/299523/cheap-handgun-scheme-misfires |title=Cheap handgun scheme misfires |work=Bangkok Post |archive-url=https://archive.today/20221123151054/https://www.bangkokpost.com/thailand/general/299523/cheap-handgun-scheme-misfires |archive-date=23 November 2022 |first=Wassayos |last=Ngamkham |date=25 June 2012}}</ref><ref>{{cite web |url=http://soha.vn/sung-ngan-ma-vang-thiet-ke-rieng-cho-tong-thong-my-donald-trump-20180121082708095.htm |title=Súng ngắn mạ vàng thiết kế riêng cho Tổng thống Mỹ Donald Trump |trans-title=Gold-plated pistol designed specifically for US President Donald Trump |language=vi |date=21 January 2018 |website=VCCorp.vn |access-date=April 15, 2018 |archive-url=https://web.archive.org/web/20180416073344/http://soha.vn/sung-ngan-ma-vang-thiet-ke-rieng-cho-tong-thong-my-donald-trump-20180121082708095.htm |archive-date=April 16, 2018 |url-status=live}}</ref>
{{div col end}}

==Related rounds==
{{div col}}
*[[.38/.45 Clerke|.38/45 Clerke]]
<!-- Don't fill this link. There's a .45-38 page to be moved into it shortly-->
*[[.400 Cor-Bon]]
*[[.45 Auto Rim]]
*[[.45 GAP]]
*.45 [[Peters Cartridge Company|Peters]]—Thompson shot cartridge<ref>{{Cite journal |url=http://www.saf.org/LawReviews/PSharpe1.html |title=The Thompson Sub-Machine Gun |first=Philip B. |last=Sharpe |date=March–April 1933 |volume=23 |number=6 |journal=[[Journal of Criminal Law & Criminology|Journal of the American Institute of Criminal Law and Criminology]] |pages=1098–1114 |via=Second Amendment Foundation |access-date=November 11, 2014 |archive-url=https://web.archive.org/web/20000816062444/http://www.saf.org/LawReviews/PSharpe1.html |archive-date=August 16, 2000 |url-status=dead}}</ref>
*[[.45 Remington–Thompson]]
*[[.45 Super]]
*[[.45 Winchester Magnum]]
*[[.45 Super#.450 SMC|.450 SMC]]
*[[.451 Detonics Magnum]]<ref name="Detonics .451 History">{{cite web |url=http://www.z3bigdaddy.com/site8/page44.html |title=Short History of the .451 Detonics Magnum |date=2012-08-05 |website=Site8 |access-date=June 24, 2015 |archive-url=https://web.archive.org/web/20150623233828/http://www.z3bigdaddy.com/site8/page44.html |archive-date=June 23, 2015 |url-status=dead}}</ref>
*[[.460 Rowland]]
*[[.50 GI]]<ref>{{cite web |url=http://tincanbandit.blogspot.com/2014/10/cartridge-interchangeability.html |title=Cartridge Interchangeability |date=October 15, 2014 |website=TINCANBANDIT's Gunsmithing |access-date=June 24, 2015 |archive-url=https://web.archive.org/web/20150624045158/http://tincanbandit.blogspot.com/2014/10/cartridge-interchangeability.html |archive-date=June 24, 2015 |url-status=live}}</ref>
{{div col end}}

==See also==
*[[List of .45 caliber handguns]]
*[[Table of handgun and rifle cartridges]]

==Notes==
{{reflist|group=note}}

==References==
===Citations===
{{Reflist}}

===Sources===
{{refbegin}}
*{{cite book |author=U.S. Army Ordnance Department |author-link1=United States Army Ordnance Corps |title=Description of the Automatic Pistol, Caliber .45, Model of 1911, with Rules for Management, Memoranda of Trajectory, and Description of Ammunition |year=1917 |publisher=[[United States Government Publishing Office|U.S. Government Printing Office]] |location=Washington, DC |url=https://archive.org/details/descriptionofaut00unitrich}} Official U.S. Army description of the original [[M1911 pistol|Model 1911 pistol]], including its .45 ACP ammunition.
{{refend}}

==External links==
{{Commons category}}
*{{cite web |url=http://www.stoppingpower.info/index.php/.45 |title=The model 1911 |website=stoppingpower.info|archive-url=https://web.archive.org/web/20070920010354/http://www.stoppingpower.info/index.php/.45 |archive-date=September 20, 2007 }}
*{{cite web |url=http://www.ballisticsbytheinch.com/45auto.html |title=.45 ACP Results in fps |website=Ballistics By The Inch}}
*{{cite web |url=http://www.saami.org/PubResources/CC_Drawings/Pistol/45%20Automatic.pdf |title=SAAMI Specification|archive-url=https://web.archive.org/web/20120403204550/http://www.saami.org/PubResources/CC_Drawings/Pistol/45%20Automatic.pdf |archive-date=April 3, 2012 }}

{{John Browning}}
{{Colt's Manufacturing Company}}
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{{WWIIUSInfWeaponsNav}}
{{WWIIChineseInfantryWeapons}}
{{WW2 Brit Comm infantry guns}}
{{Soviet infantry weapons of World War II}}
{{Modern US Infantry Weapons}}

{{DEFAULTSORT:45 Acp}}
[[Category:Pistol and rifle cartridges]]
[[Category:Military cartridges]]
[[Category:.45 ACP firearms]]
[[Category:Colt cartridges]]