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 230 gr (15 g; 0.53 oz) round-nose bullet at approximately 830 ft/s (250 m/s) fired from a government-issue M1911A1 pistol.

Since standard-pressure .45 ACP rounds are subsonic when fired from handguns and submachine guns, it is a useful caliber for suppressed weapons to eliminate the sonic boom.

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.

[13] According to Commission internationale permanente pour l'épreuve des armes à feu portatives (CIP) rulings, the .45 ACP cartridge case can handle up to 131 MPa (19,000 psi) Pmax piezo pressure.

In CIP-regulated countries every pistol cartridge combination has to be 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 170 MPa (25,000 psi) PE piezo pressure.

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).

In its non-expanding 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.

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.

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.

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 1,087 ft/s (331 m/s) speed of sound at 32 °F (0 °C) 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.

Most .45 ACP suppressors must be fired "wet" (with an ablative medium, usually oil or water) to bring sound levels down to "hearing-safe" (under 140 dB, generally).

Standard (not extended) single-stack magazines for pistols based on the 1911 design commonly, hold eight rounds or fewer in .45 ACP.

This is a common practice for updating older cartridges to match the better quality of materials and workmanship in modern firearms.

[20] The Super is dimensionally identical to the .45 ACP; however, the cartridge carries a developer established pressure of 28,500 psi (197 MPa) and requires minor modification of firearms for use.