45 Automatic (45 Auto)

Also known as

45 Auto
.45 Auto
45 ACP
.45 ACP
45 Automatic Colt Pistol

45 Automatic (45 Auto) is SAAMI's recognized name for the classic U.S. centerfire pistol cartridge chambered by the Glock 21 family. SAAMI publishes the standardized 45 Auto / 45 Auto +P drawing and pressure standard, while Federal Premium, Remington, and Winchester still sell current commercial loads.

45 Automatic (45 Auto), SAAMI-recognized pistol cartridge, Munitions

Image source: 45 ACP - FMJ - SB - 3.jpg

Profile / Specs

Profile

Origin: United States
Built by: Federal PremiumRemingtonWinchester
Type: SAAMI-recognized pistol cartridge
Service note: Early 20th century to present
Designer: John Moses Browning / Colt
Designed: 1904-1911
Unit cost: $38.99 per 50-round box of American Eagle Handgun, 45 Auto, 230 Grain, Full Metal Jacket, 890 fps
Produced: 1911-present

cartridge ammunition pistol

Specifications

SAAMI name: 45 Automatic (45 Auto)
SAAMI MAP: 21,000 psi
Case length: 0.898 in (22.81 mm)
Overall length: 1.190-1.275 in (30.23-32.39 mm)
Bullet diameter: .4520 in (11.481 mm)
Representative load: 230-grain FMJ, 890 fps

Variants

45 Automatic +P
45 Automatic Match

Compatible Firearms

SAAMI recognizes 45 Automatic as the correct cartridge name, and GLOCK lists the G21 Gen4 as chambered in .45 Auto.

Compatible item

Item type

Compatibility evidence

Glock 21, .45 Auto semi-automatic pistol, Infantry Weapons

Semi-automatic pistol

GLOCK identifies the G21 Gen4 as chambered in .45 Auto, which is the same cartridge SAAMI recognizes as 45 Automatic (45 Auto).

Sources: SAAMI FAQs, GLOCK 21 Gen4

Service And Conflict Use

Service History

In service: Commercial centerfire pistol cartridge standardized by SAAMI as 45 Automatic (45 Auto).

Media

45 Automatic (45 Auto) Images

45 Automatic (45 Auto), SAAMI-recognized pistol cartridge, Munitions - view 1 — Source: .45 ACP dimensions.svg

45 Automatic (45 Auto), SAAMI-recognized pistol cartridge, Munitions - view 2 — Source: .45 ACP U.S. Army ball cartridge diagram.jpg

Related Weapon Systems

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Sources

SAAMI FAQsPublisher: SAAMI | Note: Supports the recognized cartridge name 45 Automatic (45 Auto) and the .45 Auto / .45 ACP naming convention. | Accessed: 2026-06-27 Generally Accepted Cartridge and Chamber NamesPublisher: SAAMI | Note: Supports the 45 Automatic, 45 AUTO, and 45 ACP naming variants used in the standards catalog. | Accessed: 2026-06-27 SAAMI Z299.3-2022Publisher: SAAMI | Note: Supports the 45 Automatic chamber drawing and pressure standard used for the cartridge specifications. | Accessed: 2026-06-27 The .45 ACP: History & PerformancePublisher: American Rifleman | Note: Supports the cartridge's early 20th century U.S. development context and Browning/Colt design background. | Accessed: 2026-06-27 GLOCK 21 Gen4Publisher: GLOCK | Note: Supports the G21 Gen4 chambering in .45 Auto and the direct compatibility link used on this cartridge page. | Accessed: 2026-06-27 Shop products in 45 Auto today | Federal PremiumPublisher: Federal Premium | Note: Supports current 45 Auto load examples and retail price context, including American Eagle Handgun 230-grain FMJ pricing. | Accessed: 2026-06-27 45 ACP Ammo - RemingtonPublisher: Remington | Note: Supports 45 ACP / 45 Auto commercial naming and current handgun-ammunition background context. | Accessed: 2026-06-27 USA45AVP | Winchester AmmunitionPublisher: Winchester Ammunition | Note: Supports current 45 Auto handgun-ammunition context and commercial load availability. | Accessed: 2026-06-27 45 ACP - FMJ - SB - 3.jpgPublisher: Wikimedia Commons | Note: Image provenance for the primary 45 Auto cartridge photograph. | Accessed: 2026-06-27 .45 ACP dimensions.svgPublisher: Wikimedia Commons | Note: Image provenance for a cartridge dimensions diagram showing 45 ACP / 45 Auto measurements. | Accessed: 2026-06-27 .45 ACP U.S. Army ball cartridge diagram.jpgPublisher: Wikimedia Commons | Note: Image provenance for an historical 45 ACP cartridge diagram. | Accessed: 2026-06-27