_45 Automatic-1

Hang onto your boots, There is no such cartridge as the .45 ACP

Calm down and take a breath, I am not messing with you I promise. I expect this article will stir up a bunch of controversy but that is not my intention. I hear so many people refer to the .45 Automatic or .45 Auto as the .45 ACP and that is truly incorrect.

Here is my argument, first of all you see the in the above photo the rollmark on a Colt M1991A1 barrel hood and like all Colts and other handguns chambered in the .45 Auto cartridge the barrel hood is rollmarked as such. ACP stands for Automatic Colt Pistol and is the platform the .45 Auto cartridge is fired from.

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Next up, when you go buy a box of cartridges for your .45 Auto pistol, even in you ask for .45 ACP, the box and headstamps are marked .45 Auto.

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Next up of the 9th edition of the Hornady manual on page 850 Hornady explains how, though the cartridge is often referred to .45 ACP this is incorrect. I read the exact words in the video.

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In the past few years I have heard of firearms and cartridge boxes marked .45 ACP so here I present the indisputable evidence,  straight from SAAMI. SAMMI is Sporting Arms and Ammunition Manufacturers’ Institute. From their website ” SAAMI is an association of the nation’s leading manufacturers of firearms, ammunition and components. SAAMI was founded in 1926 at the request of the federal government and tasked with:

  • Creating and publishing industry standards for safety, interchangeability, reliability and quality
  • Coordinating technical data
  • Promoting safe and responsible firearms use

The work at SAAMI is accomplished by its committees. Technical excellence is always our goal and safety is always the prerequisite.”

So SAAMI is the governing body on cartridges, their dimensions, pressure ceilings, and chamber dimensions. As far as who has the final word, it is they.

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Search SAAMI for .45 ACP, and no one is home.

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Search for .45 Automatic and you have the option to download a few PDFs with detailed information of the .45 Automatic cartridge.

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Here is the contents page leading to the info, notice .45 ACP is not listed while .45 Automatic is.

I am not doing publishing this article to upset anyone or rock the boat but solely in the interest in providing correct information. The better we are all educated the better off we all are. I see many people ask if .45 ACP and .45 Automatic is the same cartridge and so with such misinformation, many people go in to their gunstore asking for one thing and get another.

I myself went into a local gunstore and asked for a box of .45 Automatic and they guy behind the counter asked me if I meant .45 ACP, I said not I want .45 Auto and he looked me straight in the eyes and told me “I don’t think you know what you want maybe you should learn about handguns before you get one” This was not that long ago and can you imagine what I wanted to tell this idiot. Fortunately an older gentleman, working there, walked a box of .45 Auto to the counter and sat it down and said “This is what he wants”.  The guy said, yea .45 ACP .Do you care to guess how the box and case head was marked because I damned sure showed him the .45 Auto label.

The ACP designation hearkens back to a time when Colt was the only commercial producer of the Government Model .45 Automatic pistol. I’ve seen very old cartridge boxes marked 45 Automatic, Colt Pistol. Read that again. 45 Automatic…comma…Colt Pistol. The comma carries weight. I’ve also seen a few marked Colt .45 Automatic, Rimless Smokeless Cartridges. Sometime in the 30s, Automatic, Colt Pistol was abbreviated as A.C.P. for the sake of brevity, and shortly after it became simply ACP in general conversation…for the same reasons. So, while the technical term for the cartridge itself is .45 Automatic…recently shortened to .45 Auto…the ammunition manufacturers can be blamed for its being incorrectly referred to as ACP. The smaller centerfire cartridges that Colt’s pistols were chambered for were also labeled as .25/32/380 Automatic, Colt Pistol…but for some reason they stuck while their big brother went on to cause inane arguments on the internet. – John Travis

  U.M.C. .45 A.C.P. was the cartridge that came before the .45 Automatic but they are not the same.  The official designation is ” Cal. .45 Automatic Pistol Ball Cartridge, Model of 1911“.

Please watch the video and lets start a discussion on this topic.

Thanks to SAAMI for the information and keeping us straight.


By Hunter Elliott

I spent much of my youth involved with firearms and felt the call early on to the United States Marine Corps, following in my father's and his brother's footsteps. Just after high school I enlisted and felt most at home on the rifle range, where I qualified expert with several firearms and spent some time as a rifle coach to my fellow Marines. After being honorably discharged I continued teaching firearm safety, rifle and pistol marksmanship, and began teaching metallic cartridge reloading. In the late 1990s I became a life member to the National Rifle Association and worked with the Friends of the NRA. Around that time my father and I became involved with IDPA and competed together up until he passed away. I began reviewing firearms for publications in the mid 2000s and have been fortunate to make many friends in the industry. Continuing to improve my firearms skills and knowledge is a never ending journey in which we should all be committed. I am also credited as weapons master on a few independent films.

51 thoughts on “There is no such cartridge as the .45 ACP”
    1. Nevertheless, the cartridge is .45 Automatic as it was invented and named by John Browning and that is supported by SAAMI.
      SAAMI holds correctness over the BATF, FBI, and and advertisement, I promise.
      Could you find me specifications on a .45 ACP cartridge that are backed up by consistent documentation?

      1. In a court of law (the official word), it is unlikely referring to “.45 Auto” as “.45 ACP” would be accepted as a non existent entity. On this blog ….you may have a point.

      2. Belated 6 yrs maybe, but I must try to respond; this article is “technically correct”. Thanks;
        And; too many courts, and government agencies are often wrong. Who trusts the Feds?
        As a matter of fact, this is like -Democracy? What Democracy? It’s supposed to be a Republic! Const Art IV Sec 4; And; “Representative Democracy” is an Oxymoron. How many People pledge allegiance to the flag, and to the Democracy …? Now let’s trash the 17th Amendment.

    2. Well I’m glad you have this small terminological victory to hold on to. However you seem to lack the confidence in yourself to fight the larger battle. Yeah, that’s right, the hordes of people saying “.45 long colt” (that there was sarcasm)

  1. That is very interesting to know never even looked into that or ever considered that it never existed after seeing it used so many times throughout YouTube videos hearing people talk and ect. I have even used it myself and now I’m starting to think I feel like a dumbass lol But then again I have a Rock Island armory 1911a1 CS manufactured by armscor of course the magazine even has 45 ACP on it hard to believe A manufacturer as large as them would put that on there magazines if it didn’t exist or so per se Incorrect Term

  2. The 1920 vintage Peters advertisement predates the creation of SAAMI by approximately six years. It may only be a colloquial designation, but it is a very old one.

    I did some more digging and found a reference to “.45 ACP” dating to the December 1906 edition of “Recreation” magazine. This letter to the editor can be on Pg 591:


    Clearly, some individuals were using that colloquial name nearly twenty years before SAAMI was created. So we need to ask from whence it came. Hackley, Woodin and Scranton’s “History of Modern U. S. Military Small Arms Ammunition – Volume 1: 1880-1939” indicates that Union Metallic Cartridge (UMC) was using the headstamp “.45 ACP” as early as 1907. UMC is known to have used ACP headstamps for all of the Colt Automatic cartridges, except for the .380 which was stamped “.380 CAPH.” (CAPH = Colt Automatic Pistol Hammerless)

  3. I’ve found even earlier usage of the “.45 ACP” headstamp. John Potocki’s “The Colt Model 1905 Automatic Pistol” reproduces pages from a September 1905 Colt catalog. One of the pages referencing the new M1905 pistol illustrates the cartridge with the headstamp “.45 ACP” as loaded by UMC.

  4. It has taken awhile for the handloading companies to get on board, Lyman (1970) and Speer (~1978) reference 45ACP, current European powder manufacturer Vihtavhuori still uses the name 45ACP; but states, “designated by CIP as 45auto.” (I believe CIP is the European SAAMI). Current Lyman and Speer manuals use the term 45auto/Automatic with 45ACP in parenthesis.

    Good article, and then there’s the 38Super. 🙂

    Not sure when I began using the term 45auto, probably in the early ’70s because 45auto was on a National Match Colt 1911barrel and on ammunition boxes, still use it on all the Internet forums I’m a member of.

      1. And S&W created, still makes .38 Special, along with other third parties. But the bullit is .354, not .38. So it fits a .357 Mag chamber. Is that explainable? Is .380 Auto even .38? What about .38 Super, or the old .38 Long Colt? Confusion plus?

  5. I agree with your thought process and premise for the article and I am also the same person that cringes when someone doesn’t know the difference between .45 Auto/Automatic or clip and magazine, but I also cringe when I hear the word – idea, pronounced as if it had the letter r in the spelling. There is no letter r in the spelling of the word – idea and there is no pronounced letter r when speaking the word – idea. Other than that, it was a cringe free report!

      1. Aren’t we all…currently reside in Raleigh NC… – I’ve been in NC so long now that they have dropped the “Damn” from “…Yankee”, Watch for your post religiously… keep it up!

    1. There is no recognized authority for the naming of ammunition that was invented before the present so-called authoritative organizations. This subject is as pointless as 45 Colt, 45LC, etc. It IS what popular usage becomes. Especially since the digital age has eliminated the ultimate authority — the dictionary. We all know what 45ACP means as well as 45 auto. I have my pet peeves in the area of incorrect grammar, and it’s a long list. The worst is “myself”. There is only one correct usage of the word — and that is in its proper reflexive mode: ” I shot myself in the foot”. To say John and myself were there is simply wrong. The rule is eliminate the other name or pronoun; e.g, Myself was there is stupid –No discussion required. Same for the objective case — They saw John and myself there.., Really? “They saw myself there”?. However, common incorrect usage is becoming so prevalent, that it is a lost cause right up there with the Civil War! Another one I hate is “phenomena” used for a singular event. It is “one phenomenon, two phenomena”. Ditto for our young military boys coming back from Iraq saying the word cache as “cashay” rather than its correct “cash”, and most of them know it’s wrong but don’t care!

      The best example for how futile it is to argue these things is the awful grammar that most recent college grads use: “me and her used to go there all the time”. Use the rule: : “me went there..” Or “her went there…”

      45acp or 45 auto… Does it really matter?

      1. I see what you are saying and I do believe it does matter. I see people, new to 1911s, ask on a regular basis will their pistol chambered in .45 Auto safely fire .45 ACP and vise versa. It is the subject of a lot of confusion to people new to the platform. The see guns marked one way and ammo marked the other. Call it what you will but I believe it is a least good to know the correct terminology.
        Also, I know my grammar is not the best but I do what I can.

        1. My answer would be: ” same thing”:. End of discussion. It is highly unlikely that anyone would need anymore than that. And if they do, they can Google such stuff as this!

          BTW, I’m no English teacher. What grammar I know, I learned in 3 or 4 yrs in elementary school in the late forties. (It was called Grammar School back then. I’m not sure it’s even taught nowadays!).

          Standardization after the fact is very unsatisfying. Take a few examples: Hertz rather than cycles per second, metric anything!, “on air” rather “on the air”, “on orbit” rather than “in orbit”, only 8 planets instead of 9!, celcius rather than farenheit – but I guess that’s just another metric. Speaking of which, 9mm is fine cuz that’s the way it also has been. Trying to changes things after decades is where I have a problem. I like to shoot .45 caliber, not 11.43mm! And what would we call .38 spl if we redined it in metric terms? The bullet isn’t .38 cal as anyone knows. It’s .357 cal. The name survives some 19th century naming convention in the US that uses the chamber diameter instead of bore.

          Technically, you are correct. But as you can tell, it is difficult for old fogeys to change terminology they have used for decades!

          Interesting article!

        2. I believe both are correct. It’s like arguing a Chevy is really a Chevrolet. It pointless to argue the difference as both are one and the same. If they are new to the sport there are many dual terms they will have to learn. They will also have to learn that a .45 Auto Rim is not a .45 Auto. Beginners will always experience confusion regardless of terms. It’s how we learn.

    2. No less a personage than JFK added an R to the end of words that didn’t end in R. And he didn’t pronounce the R at the end of most words that ended in R. Now I grew up in the Old South (actually the Republic of Texas!) but I served.the US of A Army 1964-1966 and I respect JFK for many things, not the least of which was his bravery and service during the Pacific War! When he said “Afriker” and “I pahked my cah..” the first few times I heard it, I found it curious. However, I researched it and found that it is common in many dialects of English around the world, including some areas of the southern United States, as well as New England. Look it up. Like Yogi said, you can see a lot by looking!

  6. There are cartridges stamped with ACP. and the barrel of my Rock Island is stamped “Cal. 45 ACP”. Just Saying! Many companies mark there boxes of ammo as ACP also.

    1. It certainly is common place enough to be accepted but by the same logic, all skid steel loaders are not Bobcats. it really does not matter to me what folks call the cartridge it was just my attempt to educate my readers by using sources such as Hornady and SAAMI.

    2. This is a “war of words”…meaningless! My RIA 1911 barrel hood also is marked “.45ACP” and that is what it is.

  7. I have many 1911’s and other 45 auto weapons and I always considered the ACP markings on these weapons a sign of respect for Browning and Colt for making the best hand gun ever created.

  8. Very interesting article and enjoyed reading it, also photography great. Also enjoyed reading the comments interesting.

    Thank you.

  9. Thank you for bringing issue this to attention.. I have known that ( ACP) stands for ” Automatic Colt Pistol” my entire life.. It has driven me half nutty when I heard someone use this term to describe a Cartridge,, and not the weapon itself.
    Improper identification of cartridges or weapons has created meant problems in the past,. I really hope people who thought this was a cartridge designation will take note and avoid further confusion in the future.

    1. As you can see I have plenty to write about.
      Maybe to your surprise most of the feedback was positive but you can’t help everyone. Point in case.
      Thank you for your feedback nevertheless.

  10. Great article. I first became aware of the different uses for this cartridge when I was issued an M3 and told to get some ammo and get familiar with it. It was January 1953, “I” Co. !7th Regt. in the Chorwon area. I turned in my M1, got the M3, and .45 AUTO ammo from the company armorer who ran me through the drill on how it worked and the why of it all. The ammo boxes were clearly marked – Cartridges – Cal. 45AUTO in magazines for M3A1. Not a sign of the expression ACP. I never heard of that until a teen age hardware store clerk squared me away one day in the 1970’s. Of course those cartridges could have been used in the Marine Corps Reisings, everybody’s M1911A1’s, Thompson 45 cal. sub-machine guns, or the M3’s we had.

    Loved the article – keep them coming!

    1. Mr. Funk, thank you for your kind words and service. I appreciate your support for my article on this. I have gotten a tremendous amount of criticism but also a lot of support. Yours is a excellent story about the .45 Auto in service.

  11. Just for grins, I looked in my Lyman 45th reloading edition and they list loadings for the .45 A.P.C..

    Only stating what I found.

    More moon shine, please.


  12. ACP does not mean “Automatic Colt Pistol”. ACP refers to the type of ammunition and not the gun it is fired from. Just like pinfire, rimfire, rimmed, rimless, all pertain to the type of ammo. And ACP stands for automatic CENTERFIRE pistol which is the type of ammo that Colt builds guns for.

      1. Just found your stuff, LOVE it. Am from the Carolinas also. Siler City of all places. Carry on,Sir
        AND no Mayberry insight.LOL

  13. Thanks, I always like learning something new. Don’t let the moes (as in the stooges) get you down. Having the correct information is always best! Good job.

  14. I’m sure at some point in history the idea of saving in printing came into play. 7 vs 8 letters to print and the micro amount of ink that would be saved or time in stamping stamp.

    .45 ACP is also known as .45 Auto or .45 Automatic.

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