A question that come up regularly is what walk ACP stand for as soon as it concerns guns and also ammo. We see the phrase often, and how that came around is a very interesting story.

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In this article, I setup on answering that question for you and also giving girlfriend the background of howACP fits into modern firearms. Here"s the basic answer:

ACP = automatic Colt Pistol

Check the end the video next if you want the rapid answer and also stick about for the remainder of the write-up if you desire the full scoop.


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Most that us recognize this:

The development of the automatic pistol adjusted the see of firearms.

But there to be a catch...

The development of reasonably compact, slim semi-automatic pistols required a standardization of caliber.

Here"s why:

Many revolvers compelled rimmed rounds that remained seated in the cylinder after gift discharged.

However, semiautomatic pistols, such as the Colt 1911, go not need rimmed rounds.

In fact, having actually a in salt that exceeded the diameter the the bullet would cause the round casing to catch or snag.

The many notable example of this brand-new era the semi-automatic pistols is the Colt 1911, designed by man Browning.

Browning well-known that the Colt 1911 required a round that would certainly eject after gift discharged and would load conveniently into a magazine.

For those that have actually owned or shooting the pistol before, you know it takes a very particular caliber of ring – the .45 ACP.

This leader to the key question, i m sorry we will certainly answer next.

What does ACP stand For?

The abbreviation stands for Automatic Colt Pistol. The dual meaning behind this abbreviation is:

inform the engineer or armorerinform the customer

By tying to the round, it specified that Colt draft this round specifically for their pistols.

That is clever marketing, right?

The difference needed to it is in made indigenous an engineering standpoint and for the consumer.

Browning labeling these brand-new pistol rounds – such together the .32 or .45 auto – as Automatic Colt Pistol rounds. This became abbreviated simply asACP.

Same Caliber, various Bullet

Now, a round favor the .45 ACP is no interchangeable v the various other varieties that .45 caliber rounds on the market.

A notable instance would be the .45 Colt – otherwise recognized as the .45 lengthy Colt.

The large difference in between a .45 ACP and also a .45 Colt round is 10 millimeter of added length come the long Colt and also a protruding rim at its base.

This made the .45 Colt ideal for revolvers. The .45 ACP round to be made just for semi-automatic pistols.

Revolvers, such as the M1917 Revolver made by Colt, have the right to accept ACP rounds.

However, many revolvers are built for rimmed cartridges and the ACP round does not have a protruded rim.

It would be attention to fill a .45 ACP into a .45 Colt revolver. It would certainly be disastrous to pack a .45 Colt into a pistol that accepted .45 ACP.

Both rounds have different dimensions even though they are the exact same caliber.


The loss of length on the .45 ACP also sacrifices the rate of the bullet. But, the .45 ACP is just one example of rather a couple of Automatic Colt Pistol calibers.

Colt invented a large variety that firearms. It ended up being necessary to start referring to every caliber through a device that made sense for the company.

A couple of notable automatic Colt Pistol calibers include: .25, .32, .380, .38, and .45.

All of this calibers room denoted with an “ACP” in ~ the finish of them. However, this rounds are also referred to as “auto.”

For instance, if you walk right into a total store and ask the clerk for a situation of .32 ACP or .32 auto, he will hand you the same situation of ammunition.

There is no difference other than which system a human being uses to refer to those certain rounds.

It gets amazing when we take into consideration how these rounds fit into the hand pistol arena.

Automatic Colt Pistol Calibers

The .25, .32, .38, and .380 autos are really compact, irradiate rounds. The .380 ACP is 2 millimeters shorter than a 9 x 19 millimeter Parabellum.

This makes it really compact and also easy come fit into smaller handguns such together the Bersa Thunder or old Walther PPKs.

The .25 ACP is just three soldier of a millimeter more comprehensive and one millimeter much longer than the .22 long Rifle (5.6 x 15 millimeter).

This provides the .25 ACP an extremely light round. That is mostly discovered in highly concealable derringers and also semi-automatic pistols.

It was the initial an option of Ian Flemming as soon as he started writing about James Bond.

He was later on advised through someone much more familiar with firearms that the .25 ACP was an extremely underpowered round.

Speaking the underpowered—before innovations in the ar of smokeless pistol powder, countless of the automatically Colt Pistol ring were considered to be very underpowered.

The .25 and .32 ACP room still supplied by part European police forces. The .380 Auto is incredibly popular together a concealed bring handgun caliber, yet many world complain about the penetration the this round versus ballistic gel.


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Out of all of the rounds, the .45 ACP came to be the most notorious due to the fact that it was offered in the Thompson submachine gun and the Colt 1911A1 semi-automatic pistol.

It earn its ar in American nostalgia.

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The just round come no much longer be in active production is the .38 ACP.

The .38 ACP was an effort to carry the caliber from the people of detective revolvers to pistols.

It never really took off. Sig Sauer freshly attempted to bring the caliber back in your line that pistols and that round is now recognized as the .38 SIG.

In state of protecting against power and also potential, the .38 has always been underpowered in comparison to its larger, more powerful .357 Magnum cousin.

Colt Was not the Only firm to placed Its Name into Calibers

While we may recognize famous calibers such together the .45 ACP or .380 ACP, that is important to realize Colt was no the only company to usage this trick.

As pointed out earlier, Sig Sauer produces guns chambered in .38 SIG. A few other noteworthy cartridges that bear their maker"s note include:

.300 Winchester Magnum (7.62 x 67millimeter).30-06 Springfield(7.62 x 63 millimeter) .308 Winchester (7.62 x 51 millimeter) .40 S&W (Smith & Wesson, a 10 millimeter short)